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  Subjects -> MILITARY (Total: 108 journals)
Showing 1 - 24 of 24 Journals sorted alphabetically
Africa Conflict Monitor     Full-text available via subscription   (Followers: 8)
Armed Conflict Survey     Full-text available via subscription   (Followers: 15)
Armed Forces & Society     Hybrid Journal   (Followers: 24)
Arms & Armour     Hybrid Journal   (Followers: 10)
British Journal for Military History     Open Access   (Followers: 40)
Bulletin of the Atomic Scientists     Hybrid Journal   (Followers: 6)
Ciencia y Poder Aéreo     Open Access   (Followers: 2)
Civil Wars     Hybrid Journal   (Followers: 21)
Coleção Meira Mattos : Revista das Ciências Militares     Open Access  
Conflict, Security & Development     Hybrid Journal   (Followers: 426)
Critical Military Studies     Hybrid Journal   (Followers: 4)
CRMA Journal of Humanities and Social Sciences     Open Access   (Followers: 1)
Cuadernos de Marte     Open Access  
Defence and Peace Economics     Hybrid Journal   (Followers: 22)
Defence Science Journal     Open Access   (Followers: 40)
Defence Studies     Hybrid Journal   (Followers: 31)
Defence Technology     Open Access   (Followers: 4)
Defense & Security Analysis     Hybrid Journal   (Followers: 31)
Digital War     Hybrid Journal   (Followers: 2)
Disaster and Military Medicine     Open Access   (Followers: 5)
Doutrina Militar Terrestre em Revista     Open Access  
Eesti Sõjaajaloo Aastaraamat / Estonian Yearbook of Military History     Open Access   (Followers: 2)
EsSEX : Revista Científica     Open Access   (Followers: 1)
First World War Studies     Hybrid Journal   (Followers: 27)
Fra Krig og Fred     Open Access   (Followers: 2)
Gettysburg Magazine     Full-text available via subscription  
Great Circle: Journal of the Australian Association for Maritime History, The     Full-text available via subscription   (Followers: 7)
Headmark     Full-text available via subscription   (Followers: 2)
Human Factors and Mechanical Engineering for Defense and Safety     Hybrid Journal   (Followers: 1)
International Bibliography of Military History     Hybrid Journal   (Followers: 10)
International Journal of Intelligent Defence Support Systems     Hybrid Journal   (Followers: 5)
International Peacekeeping     Hybrid Journal   (Followers: 472)
Journal for Maritime Research     Hybrid Journal   (Followers: 12)
Journal of Bioterrorism & Biodefense     Open Access   (Followers: 6)
Journal of African Military History     Hybrid Journal   (Followers: 1)
Journal of Archives in Military Medicine     Open Access   (Followers: 3)
Journal of Chinese Military History     Hybrid Journal   (Followers: 6)
Journal of Conflict and Security Law     Hybrid Journal   (Followers: 20)
Journal of Conventional Weapons Destruction     Open Access   (Followers: 3)
Journal of Defense Modeling and Simulation : Applications, Methodology, Technology     Hybrid Journal   (Followers: 6)
Journal of Defense Studies & Resource Management     Hybrid Journal   (Followers: 2)
Journal of Military and Information Science     Open Access   (Followers: 5)
Journal of Military and Strategic Studies     Open Access   (Followers: 5)
Journal of Military and Veterans Health     Full-text available via subscription   (Followers: 10)
Journal of Military Ethics     Hybrid Journal   (Followers: 11)
Journal of Military Experience     Open Access   (Followers: 7)
Journal of Military History     Full-text available via subscription   (Followers: 34)
Journal of Military Studies     Open Access   (Followers: 5)
Journal of National Security Law & Policy     Free   (Followers: 8)
Journal of Naval Architecture and Marine Engineering     Open Access   (Followers: 5)
Journal of Naval Sciences and Engineering     Open Access   (Followers: 1)
Journal of power institutions in post-soviet societies     Open Access   (Followers: 2)
Journal of Slavic Military Studies     Hybrid Journal   (Followers: 18)
Journal of Terrorism Research     Open Access   (Followers: 26)
Journal of the Royal Army Medical Corps     Hybrid Journal   (Followers: 9)
Journal on Baltic Security     Open Access   (Followers: 3)
Martial Arts Studies     Open Access   (Followers: 1)
Media, War & Conflict     Hybrid Journal   (Followers: 15)
Medical Journal Armed Forces India     Full-text available via subscription  
Medicine, Conflict and Survival     Hybrid Journal   (Followers: 3)
Militärgeschichtliche Zeitschrift     Hybrid Journal   (Followers: 6)
Military Behavioral Health     Hybrid Journal   (Followers: 6)
Military Medical Research     Open Access   (Followers: 4)
Military Medicine     Hybrid Journal   (Followers: 9)
Military Psychology     Hybrid Journal   (Followers: 10)
Modern Information Technologies in the Sphere of Security and Defence     Open Access   (Followers: 2)
Naval Research Logistics: an International Journal     Hybrid Journal   (Followers: 3)
Nonproliferation Review     Hybrid Journal   (Followers: 5)
O Adjunto : Revista Pedagógica da Escola de Aperfeiçoamento de Sargentos das Armas     Open Access   (Followers: 2)
Perspectives on Terrorism     Open Access   (Followers: 472)
Post-Soviet Armies Newsletter     Open Access   (Followers: 1)
Problemy Mechatroniki. Uzbrojenie, lotnictwo, inżynieria bezpieczeństwa / Problems of Mechatronics. Armament, Aviation, Safety Engineering     Open Access   (Followers: 3)
Revista Agulhas Negras     Open Access   (Followers: 1)
Revista Babilônia     Open Access   (Followers: 1)
Revista Científica Fundação Osório     Open Access  
Revista Científica General José María Córdova     Open Access  
Revista Cubana de Medicina Militar     Open Access   (Followers: 1)
Revista do Exército     Open Access   (Followers: 1)
Revista Militar de Ciência e Tecnologia     Open Access   (Followers: 1)
Revista Política y Estrategia     Open Access  
Sabretache     Full-text available via subscription   (Followers: 1)
Sanidad Militar     Open Access  
Scandinavian Journal of Military Studies     Open Access   (Followers: 1)
Scientia Militaria : South African Journal of Military Studies     Open Access   (Followers: 4)
Scientific Journal of Polish Naval Academy     Open Access  
Securitologia     Open Access   (Followers: 1)
Security and Defence Quarterly     Open Access   (Followers: 7)
Security Studies     Hybrid Journal   (Followers: 48)
Signals     Full-text available via subscription   (Followers: 2)
Small Wars & Insurgencies     Hybrid Journal   (Followers: 373)
Small Wars Journal     Open Access   (Followers: 17)
Social Development & Security : Journal of Scientific Papers     Open Access   (Followers: 1)
Special Operations Journal     Hybrid Journal   (Followers: 1)
Strategic Comments     Hybrid Journal   (Followers: 6)
The Military Balance     Hybrid Journal   (Followers: 9)
The RUSI Journal     Hybrid Journal   (Followers: 17)
Transportation Research Part E: Logistics and Transportation Review     Hybrid Journal   (Followers: 22)
United Service     Full-text available via subscription   (Followers: 1)
University of Miami National Security & Armed Conflict Law Review     Open Access   (Followers: 1)
Vierteljahrshefte für Zeitgeschichte. Das zentrale Forum der Zeitgeschichtsforschung     Hybrid Journal   (Followers: 11)
Vojnotehnički Glasnik     Open Access   (Followers: 1)
Vulcan     Hybrid Journal   (Followers: 1)
War & Society     Hybrid Journal   (Followers: 26)
War in History     Hybrid Journal   (Followers: 23)
Whitehall Papers     Hybrid Journal   (Followers: 3)
Wiedza Obronna     Open Access   (Followers: 2)
Zeitschrift für Slawistik     Hybrid Journal   (Followers: 1)
선진국방연구     Open Access  

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Defence Technology
Journal Prestige (SJR): 0.633
Citation Impact (citeScore): 2
Number of Followers: 4  

  This is an Open Access Journal Open Access journal
ISSN (Print) 2214-9147
Published by Ke Ai Homepage  [71 journals]
  • Research status and development trend of MEMS S&A devices: A review

    • Abstract: Publication date: Available online 19 February 2020Source: Defence TechnologyAuthor(s): Mei Li, Tengjiang Hu MEMS Safety-and-Arming (S&A) device is the new generation of S&A device which integrates the mechanism of actuation and barrier. The features of minimized structure and easy integration make it to be the indispensable support to the development of weapon miniaturization, integration and intelligence. As a key component in the new generation weapon system, the sound development of MEMS S&A devices will have a significant impact on the future national defense system. Herein, the research status and development trend of MEMS S&A devices are introduced in this paper. From literature review on various MEMS S&A devices, it can be seen that the researches have evolved from individual components to system integration, and many prototypes have the potential for live-fire testing. Different driven principles and structures of the MEMS S&A devices are compared and summarized. At present, the MEMS S&A device can realize the mutual integration of the driving mechanism and the blocking mechanism on the micron level. In the future, with the establishment of new design criteria, MEMS S&A devices will develop from prototypes to practical applications, which will further promote the integration and intelligent of weapon systems.
  • Chain damage effects of multi-spaced plates by reactive jet impact

    • Abstract: Publication date: Available online 18 February 2020Source: Defence TechnologyAuthor(s): Yuanfeng Zheng, Chenghai Su, Huanguo Guo, Qingbo Yu, Haifu Wang Chain damage is a new phenomenon that occurs when a reactive jet impacts and penetrates multi-spaced plates. The reactive jet produces mechanical perforations on the spaced plates by its kinetic energy (KE), and then results in unusual chain rupturing effects and excessive structural damage on the spaced plates by its deflagration reaction. In the present study, the chain damage behavior is initially demonstrated by experiments. The reactive liners, composed of 26 wt%Al and 74 wt% PTFE, are fabricated through a pressing and sintering process. Three reactive liner thicknesses of 0.08 CD, 0.10 CD and 0.12 CD (charge diameter) are chosen to carry out the chain damage experiments. The results show a chain rupturing phenomenon caused by reactive jet. The constant reaction delay time and the different penetration velocities of reactive jets from liners with different thicknesses result in the variation of the deflagration position, which consequently determines the number of ruptured plates behind the armor. Then, the finite-element code AUTODYN-3D has been used to simulate the kinetic energy only-induced rupturing effects on plates, based on the mechanism of behind armor debris (BAD). The significant discrepancies between simulations and experiments indicate that one enhanced damage mechanism, the behind armor blast (BAB), has acted on the ruptured plates. Finally, a theoretical model is used to consider the BAB-induced enhancement, and the analysis shows that the rupturing area on aluminum plates depends strongly upon the KE only-induced pre-perforations, the mass of reactive materials, and the thickness of plates.
  • Damage mechanics and energy absorption capabilities of natural fiber
           reinforced elastomeric based bio composite for sacrificial structural

    • Abstract: Publication date: Available online 17 February 2020Source: Defence TechnologyAuthor(s): Vishwas Mahesh, Sharnappa Joladarashi, Satyabodh M. Kulkarni The present study deals with the experimental, finite element (FE) and analytical assessment of low ballistic impact response of proposed flexible ‘green’ composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute (JRJ), jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ). Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime. The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism. Results revealed that inclusion of natural rubber aids in better energy absorption and mitigating the failure of the proposed composite. Among the three different stacking sequences of flexible composites considered, JRJRJ provides better ballistic performance compared to its counterparts. The damage study reveals that the main mechanism of failure involved in flexible composites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposed flexible composites are free from catastrophic failure. Results obtained from experimental, FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other. The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.
  • Hypersonic impact flash characteristics of a long-rod projectile collision
           with a thin plate target

    • Abstract: Publication date: Available online 14 February 2020Source: Defence TechnologyAuthor(s): Yijiang Xue, Qingming Zhang, Danyang Liu, Renrong Long, Yangyu Lu, Tianfei Ren, Liangfei Gong Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V0) according to I∝V0n , where n = 4.41 for V0 > 2 km/s. However, for V0  2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V0. However, for V0 
  • Buckling analysis of embedded graphene oxide powder-reinforced
           nanocomposite shells

    • Abstract: Publication date: Available online 14 February 2020Source: Defence TechnologyAuthor(s): Farzad Ebrahimi, Pendar Hafezi, Ali Dabbagh In this study, the buckling analysis of a Graphene oxide powder reinforced (GOPR) nanocomposite shell is investigated. The effective material properties of the nanocomposite are estimated through Halpin-Tsai micromechanical scheme. Three distribution types of GOPs are considered, namely uniform, X and O. Also, a first-order shear deformation shell theory is incorporated with the principle of virtual work to derive the governing differential equations of the problem. The governing equations are solved via Galerkin's method, which is a powerful analytical method for static and dynamic problems. Comparison study is performed to verify the present formulation with those of previous data. New results for the buckling load of GOPR nanocomposite shells are presented regarding for different values of circumferential wave number. Besides, the influences of weight fraction of nanofillers, length and radius to thickness ratios and elastic foundation on the critical buckling loads of GOP-reinforced nanocomposite shells are explored.
  • Mechanical behavior and failure mechanism of polyurea nanocomposites under
           quasi-static and dynamic compressive loading

    • Abstract: Publication date: Available online 13 February 2020Source: Defence TechnologyAuthor(s): Qiang Liu, Peng-wan Chen, Yan-song Guo, Jian-jun Su, Lu Han, Ali Arab, Jian-fei Yuan Polyurea is an elastomeric material that can be applied to enhance the protection ability of structures under blast and impact loading. In order to study the compressive mechanical properties of SiC/polyurea nanocomposites under quasi-static and dynamic loading, a universal testing machine and split Hopkinson pressure bar (SHPB) apparatus were used respectively. The stress-strain curves were obtained on polyurea and its composites at strain rates of 0.001–8000 s−1. The results of the experiment suggested that increase in the strain rates led to the rise of the flow stress, compressive strength, strain rate sensitivity and strain energy. This indicates that all of the presented materials were dependent on strain rate. Moreover, these mechanical characters were enhanced by incorporating a small amount of SiC into polyurea matrix. The relation between yield stress and strain rates were established using the power law functions. Finally, in order to investigate the fracture surfaces and inside information of failed specimens, scanning electron microscopy (SEM) and micro X-ray computed tomography (micro-CT) were used respectively. Multiple voids, crazes, micro-cracks and cracking were observed in fracture surfaces. On the other hand, the cracking propagation was found in the micro-CT slice images. It is essential to understand the deformation and failure mechanisms in all the polyurea materials.
  • A novel approach of material nonlinear analysis in fracture mechanics

    • Abstract: Publication date: Available online 13 February 2020Source: Defence TechnologyAuthor(s): Himanshu Gaur, Anupam Shrivastav This article demonstrates the novel approach for solving fracture mechanics problems for elastic materials. In this article two problems are solved-plate with central crack and double cantilever beam specimen. The methodology solves the fracture problem with relative ease in strength of material style calculations with proper modelling and structural idealization assumptions. Use of elastic moduli in the analysis is eliminated. Instead, stress and strain functions are used which are directly derived from stress-strain curve of the material. This way, the whole stress-strain diagram is utilized in the analysis which, also, exposes the response of structure when loading is in nonlinear range of the material behaviour. Energy release rate is calculated for both of the structures and results are compared with the current state of art of fracture mechanics.
  • Fatigue crack propagation in a helicopter component subjected to impact

    • Abstract: Publication date: Available online 13 February 2020Source: Defence TechnologyAuthor(s): M. Fossati, M. Pagani, M. Giglio, A. Manes Damage tolerant methodology is increasingly used in aeronautical components, especially due the fact that the Aviation Regulation requires such an assessment in case an accidental damage occurs. At present, there is a strong and actual interest in applying such procedures to helicopter components that are subjected to high frequency cyclic loads. In this paper, an investigation on a damaged transmission shaft for a tail rotor transmission of an actual helicopter has been carried out focusing on the fatigue crack propagation. A complete sequence of experimental tests was performed in order to create an actual ballistic damage and to subsequently check the damage tolerant behaviour. The shaft was damaged by oblique ballistic impact and was subsequently subjected to torsional fatigue loading. During the fatigue cycles several cracks propagated from the ballistic damages. Both of these steps (impact and fatigue loading) were also simulated by a complex modelling approach based on Finite Element Models and fracture mechanics theory. The comparison between the experimental and numerical results shows a good agreement but it underlines the need for a very refined modelling technique capable to replicate all the features associated with the damage in order to reliably simulate the subsequent propagation phase.
  • Recursive weighted least squares estimation algorithm based on minimum
           model error principle

    • Abstract: Publication date: Available online 12 February 2020Source: Defence TechnologyAuthor(s): Xiaoyun Lei, Zhian Zhang Kalman filter is commonly used in data filtering and parameters estimation of nonlinear system, such as projectile's trajectory estimation and control. While there is a drawback that the prior error covariance matrix and filter parameters are difficult to be determined, which may result in filtering divergence. As to the problem that the accuracy of state estimation for nonlinear ballistic model strongly depends on its mathematical model, we improve the weighted least square method (WLSM) with minimum model error principle. Invariant embedding method is adopted to solve the cost function including the model error. With the knowledge of measurement data and measurement error covariance matrix, we use gradient descent algorithm to determine the weighting matrix of model error. The uncertainty and linearization error of model are recursively estimated by the proposed method, thus achieving an online filtering estimation of the observations. Simulation results indicate that the proposed recursive estimation algorithm is insensitive to initial conditions and of good robustness.
  • An interface shear damage model of chromium coating/steel substrate under
           thermal erosion load

    • Abstract: Publication date: Available online 8 February 2020Source: Defence TechnologyAuthor(s): Xiaolong Li, Yong Zang, Yong Lian, Minyu Ma, Lei Mu, Qin Qin The Cr-plated coating inside a gun barrel can effectively improve the barrel's erosion resistance and thus increase the service life. However, due to the cyclic thermal load caused by high-temperature gunpowder, micro-element damage tends to occur within the Cr coating/steel substrate interface, leading to a gradual deterioration in macro-mechanical properties for the material in the related region. In order to mimic this cyclic thermal load and, thereby, study the thermal erosion behavior of the Cr coating on the barrel's inner wall, a laser emitter is utilized in the current study. With the help of in-situ tensile test and finite element simulation results, a shear stress distribution law of the Cr coating/steel substrate and a change law of the interface ultimate shear strength are identified. Studies have shown that the Cr coating/steel substrate interface's ultimate shear strength has a significant weakening effect due to increasing temperature. In this study, the interfacial ultimate shear strength decreases from 2.57 GPa (no erosion) to 1.02 GPa (laser power is 160 W). The data from this experiment is employed to establish a Cr coating/steel substrate interface shear damage model. And this model is used to predict the flaking process of Cr coating by finite element method. The simulation results show that the increase of coating crack spacing and coating thickness will increase the service life of gun barrel.
  • Reaction degree of composition B explosive with multi-layered compound
           structure protection subjected to detonation loading

    • Abstract: Publication date: Available online 8 February 2020Source: Defence TechnologyAuthor(s): Jiayun Liu, Yongxiang Dong, Xuanyi An, Ping Ye, Qitian Sun, Qian Gao The explosive reaction degree and protection from explosions are concerns in the military field. In this work, the reaction degree of the composition B explosive was investigated experimentally. Multi-layered compound structures were used as barriers to weaken the blast loads. A comprehensive experiment using a high-speed camera and image processing techniques, side witness plates, and bottom witness plates was presented. Using the experimental fragment velocities, fragment piercing patterns, and damage characteristics, the reaction degree of the explosive impeded by different multi-layered compound structures could be precisely differentiated. Reaction parameters of the explosive obstructed by compound structures were obtained by theoretical analysis and numerical simulations. Unlike the common method in which the explosive reaction degree is only distinguished based on the initial pressure amplitude transmitted into the explosive, a following shock wave reflected from the side steel casing was also considered. Different detonation growth paths in the explosive formed. Therefore, all these shock wave propagation characteristics must be considered to analyze the explosive response impeded by compound structures.
  • Increasing of photostability of HNS explosive in the presence of UV

    • Abstract: Publication date: Available online 6 February 2020Source: Defence TechnologyAuthor(s): Hamid Reza Pouretedal, Sajjad Damiri, Zynab Karami The photostabilies of hexanitrostillbene (HNS) were studied at 1% wt. of photostabilizers. The photostabilizers of Chiguard BP-12 (UV- 531), ADK STAB LA-326 (UV- 326), ADK STAB LA-32 (UV-P), Irganox 1010 and Everstab LS944 were used in this study. A photoreactor including a 30 W monochromatic UV lamp was used for investigation of photodegradations of solid HNS. The changes in surface area of HNS peak in HPLC chromatogram at time intervals of 2, 4, 6 and 8 h were used for calculation of kinetic rate constants of photodegradation process. The compound of UV-P photostabilizer was found to have the greatest effect on enhancing photostability for HNS among the investigated photostabilizers. The kinetic rate constants were obtained 6.2 × 10−2 and 4.1 × 10−2 h−1, respectively, for photodegradation process of HNS in absence and in presence of UV-P.
  • Force chains based mesoscale simulation on the dynamic response of Al-PTFE
           granular composites

    • Abstract: Publication date: Available online 28 January 2020Source: Defence TechnologyAuthor(s): Le Tang, Chao Ge, Huan-guo Guo, Qing-bo Yu, Hai-fu Wang Force chains based mesoscale simulation is conducted to investigate the response behavior of aluminum-polytetrafluoroethylene (Al-PTFE) granular composites under a low-velocity impact. A two-dimensional model followed the randomly normal distribution of real Al particles size is developed. The dynamic compressive process of Al-PTFE composites with varied Al mass fraction is simulated and validated against the experiments. The results indicate that, force chains behavior governed by the number and the size of agglomerated Al particles, significantly affects the impact response of the material. The failure mode of the material evolves from shear failure of matrix to debonding failure of particles with increasing density. A high crack area of the material is critical mechanism to arouse the initiation reaction. The damage maintained by force chains during large plastic strain builds up more local stresses concentration to enhance a possible reaction performance. In addition, simulation is performed with identical mass fraction but various Al size distribution to explore the effects of size centralization and dispersion on the mechanical properties of materials. It is found that smaller sized Al particle of composites are more preferred than its bulky material in ultimate strength. Increasing dispersed degree is facilitated to create stable force chains in samples with comparable particle number. The simulation studies provide further insights into the plastic deformation, failure mechanism, and possible energy release capacity for Al-PTFE composites, which is helpful for further design and application of reactive materials.
  • Aerodynamics analysis of a hypersonic electromagnetic gun launched

    • Abstract: Publication date: Available online 21 January 2020Source: Defence TechnologyAuthor(s): Jian Shen, Shaobo Fan, Yaxin Ji, Qingyu Zhu, Ji Duan A hypersonic aerodynamics analysis of an electromagnetic gun (EM gun) launched projectile configuration is undertaken in order to ameliorate the basic aerodynamic characteristics in comparison with the regular projectile layout. Static margin and pendulum motion analysis models have been applied to evaluate the flight stability of a new airframe configuration. With a steady state computational fluid dynamics (CFD) simulation, the basic density, pressure and velocity contours of the EM gun projectile flow field at Mach number 5.0, 6.0 and 7.0 (angle of attack = 0°) have been analyzed. Furthermore, the static margin values are enhanced dramatically for the EM gun projectile with configuration optimization. Drag, lift and pitch property variations are all illustrated with the changes of Mach number and angle of attack. A particle ballistic calculation was completed for the pendulum analysis. The results show that the configuration optimized projectile, launched from the EM gun at Mach number 5.0 to 7.0, acts in a much more stable way than the projectiles with regular aerodynamic layout.
  • Vibration analysis of fluid-conveying multi-scale hybrid nanocomposite
           shells with respect to agglomeration of nanofillers

    • Abstract: Publication date: Available online 19 January 2020Source: Defence TechnologyAuthor(s): Farzad Ebrahimi, Ali Dabbagh The vibration problem of a fluid conveying cylindrical shell consisted of newly developed multi-scale hybrid nanocomposites is solved in the present manuscript within the framework of an analytical solution. The consistent material is considered to be made from an initial matrix strengthened via both macro- and nano-scale reinforcements. The influence of nanofillers' agglomeration, generated due to the high surface to volume ratio in nanostructures, is included by implementing Eshelby-Mori-Tanaka homogenization scheme. Afterwards, the equivalent material properties of the carbon nanotube reinforced (CNTR) nanocomposite are coupled with those of CFs within the framework of a modified rule of mixture. On the other hand, the influences of viscous flow are covered by extending the Navier-Stokes equation for cylinders. A cylindrical coordinate system is chosen and mixed with the infinitesimal strains of first-order shear deformation theory of shells to obtain the motion equations on the basis of the dynamic form of principle of virtual work. Next, the achieved governing equations will be solved by Galerkin's method to reach the natural frequency of the structure for both simply supported and clamped boundary conditions. Presenting a set of illustrations, effects of each parameter on the dimensionless frequency of nanocomposite shells will be shown graphically.
  • Strain concentration caused by the closed end contributes to cartridge
           case failure at the bottom

    • Abstract: Publication date: Available online 16 January 2020Source: Defence TechnologyAuthor(s): Song Cai, Jie Feng, Hui xu, Kun Liu, Zhong-xin Li, Zhi-lin Wu Ruptures at the bottom of cartridges are a common cause of failure of ammunitions, which directly threatens the safety of weapons and shooters. Based on plastic tube theory, this study analyses the radial and axial deformation of a cartridge, considering the radial constraint of the closed end at the bottom of the cartridge. Owing to the influence of the closed end, the bottom of a cartridge does not establish complete contact with the chamber. Owing to strain concentration in the non-contact area, this area is more amenable to the occurrence of cartridge rupture. This theory predicts the location of the fracture more accurately than the traditional theory. The maximum axial deformation of a cartridge comprises bending and friction deformation. The maximum strain at the bottom of the cartridge increased by 135% owing to the introduction of bending strain caused by the closed end. The strain distribution of a cartridge was measured using digital image correlation technology, and the measured result was consistent with the predicted results of the bending deformation theory and rupture case. The effects of wall thickness, radial clearance, friction coefficient, and axial clearance on the axial deformation of the cylinder were studied. Increasing the wall thickness and reducing radial clearance were found to reduce bending deformation; furthermore, lubrication and reduction in axial clearance reduce frictional deformation, which in turn reduce cartridge rupture.
  • Numerical investigation on cooling performance of filter in a pyrotechnic
           gas generator

    • Abstract: Publication date: Available online 13 January 2020Source: Defence TechnologyAuthor(s): Cheng Cheng, Xiao-bing Zhang, Chong Wang, Lu Wang As a key part of the pyrotechnic gas generator, the filter not only removes the particulate matter but also cools the hot gas to a safe level. This paper aims to improve the understanding of the basic heat and flow phenomenon in the gas generator. The pyrotechnic gas generator is modelling by a simplified filter structure with fiber arrays. A finite-volume model of the heat and fluid flow is proposed to simulate the detailed multi-dimensional flow and energy conversion behaviors. Several verification results are in good agreement with data in different references. Simulation results demonstrate that the filter can not only absorb heat from the gas but also cause the high intensity enhancement of the heat transfer. The performance difference between inline and staggered arrays is also discussed. The findings of the study put a further prediction tool for the understanding and design of the filter system with fibers.
  • Size dependent free vibration analysis of functionally graded
           piezoelectric micro/nano shell based on modified couple stress theory with
           considering thickness stretching effect

    • Abstract: Publication date: Available online 9 January 2020Source: Defence TechnologyAuthor(s): Maryam Lori Dehsaraji, Mohammad Arefi, Abbas Loghman Higher-order shear and normal deformation theory is used in this paper to account thickness stretching effect for free vibration analysis of the cylindrical micro/nano shell subjected to an applied voltage and uniform temperature rising. Size dependency is included in governing equations based on the modified couple stress theory. Hamilton's principle is used to derive governing equations of the cylindrical micro/nano shell. Solution procedure is developed using Navier technique for simply-supported boundary conditions. The numerical results are presented to investigate the effect of significant parameters such as some dimensionless geometric parameters, material properties, applied voltages and temperature rising on the free vibration responses.
  • Automated integration of real-time and non-real-time defense systems

    • Abstract: Publication date: Available online 9 January 2020Source: Defence TechnologyAuthor(s): Emre Dalkiran, Tolga Önel, Okan Topçu, Kadir Alpaslan Demir Various application domains require the integration of distributed real-time or near-real-time systems with non-real-time systems. Smart cities, smart homes, ambient intelligent systems, or network-centric defense systems are among these application domains. Data Distribution Service (DDS) is a communication mechanism based on Data-Centric Publish-Subscribe (DCPS) model. It is used for distributed systems with real-time operational constraints. Java Message Service (JMS) is a messaging standard for enterprise systems using Service Oriented Architecture (SOA) for non-real-time operations. JMS allows Java programs to exchange messages in a loosely coupled fashion. JMS also supports sending and receiving messages using a messaging queue and a publish-subscribe interface. In this article, we propose an architecture enabling the automated integration of distributed real-time and non-real-time systems. We test our proposed architecture using a distributed Command, Control, Communications, Computers, and Intelligence (C4I) system. The system has DDS-based real-time Combat Management System components deployed to naval warships, and SOA-based non-real-time Command and Control components used at headquarters. The proposed solution enables the exchange of data between these two systems efficiently. We compare the proposed solution with a similar study. Our solution is superior in terms of automation support, ease of implementation, scalability, and performance.
  • Bending and stress analysis of polymeric composite plates reinforced with
           functionally graded graphene nanoplatelets based on sinusoidal
           shear-deformation plate theory

    • Abstract: Publication date: Available online 7 January 2020Source: Defence TechnologyAuthor(s): Mohammad Arefi, Ali Tabatabaeian, Masoud Mohammadi The bending and stress analysis of a functionally graded polymer composite plate reinforced with graphene platelets are studied in this paper. The governing equations are derived by using principle of virtual work for a plate which is rested on Pasternak's foundation. Sinusoidal shear deformation theory is used to describe displacement field. Four different distribution patterns are employed in our analysis. The analytical solution is presented for a functionally graded plate to investigate the influence of important parameters. The numerical results are presented to show the deflection and stress results of the problem for four employed patterns in terms of geometric parameters such as number of layers, weight fraction and two parameters of Pasternak's foundation.
  • Numerical simulation study on penetration performance of depleted Uranium
           (DU) alloy fragments

    • Abstract: Publication date: Available online 7 January 2020Source: Defence TechnologyAuthor(s): Fu-lin Zhu Due to its high strength, high density, high hardness and good penetration capabilities, Depleted uranium alloys have already shined in armor-piercing projectiles. There should also be a lot of room for improvement in the application of fragment killing elements. Therefore, regarding the performance of the depleted uranium alloy to penetrate the target plate, further investigation is needed to analyze its advantages and disadvantages compared to tungsten alloy. To study the difference in penetration performance between depleted uranium alloy and tungsten alloy fragments, firstly, a theoretical analysis of the adiabatic shear sensitivity of DU and tungsten alloys was given from the perspective of material constitutive model. Then, taking the cylindrical fragment penetration target as the research object, the penetration process and velocity characteristics of the steel target plates penetrated by DU alloy fragment and tungsten alloy fragment were compared and analyzed, by using finite element software ANSYS/LS-DYNA and Lagrange algorithm. Lastly, the influence of different postures when impacting target and different fragment shapes on the penetration results is carried out in the research. The results show that in the penetration process of the DU and tungsten alloy fragments, the self-sharpening properties of the DU alloy can make the fragment head sharper and the penetrating ability enhance. Under the same conditions, the penetration capability of cylindrical fragment impacting target in vertical posture is better than that in horizontal posture, and the penetration capability of the spherical fragment is slightly better than that of cylindrical fragment.
  • Effect of silicon carbide and wire-mesh reinforcements in dissimilar grade
           aluminium explosive clad composites

    • Abstract: Publication date: Available online 2 January 2020Source: Defence TechnologyAuthor(s): S. Saravanan, K. Raghukandan Aluminium composites are inevitable in the manufacture of aircraft structural elements owing to less weight, superior corrosion resistance and higher specific properties. These composites reduce the weight of the aircraft, improve the fuel efficiency and enhance the maintenance duration. This study proposes the development of dissimilar grade aluminium (aluminium 1100-aluminium 5052) composites with different reinforcement's viz., stainless steel wire-mesh, silicon carbide (SiC) powders and SiC powder interspersed wire-mesh, by explosive cladding technique. Wire-mesh enhances the friction and restricts the movement of flyer plate to craft a defect free clad, while SiC particles form a band on the interface. Highest strength is obtained when SiC powder interspersed wire mesh is employed as reinforcement. The dissimilar aluminium explosive clad with SiC particle reinforcement results in lower strength, which is higher than that of the weaker parent alloy and that of the conventional dissimilar aluminium explosive clads without any reinforcement.
  • A novel facial emotion recognition scheme based on graph mining

    • Abstract: Publication date: Available online 30 December 2019Source: Defence TechnologyAuthor(s): Alia K. Hassana, Suhaila N. Mohammed Recent years have seen an explosion in graph data from a variety of scientific, social and technological fields. From these fields, emotion recognition is an interesting research area because it finds many applications in real life such as in effective social robotics to increase the interactivity of the robot with human, driver safety during driving, pain monitoring during surgery etc. A novel facial emotion recognition based on graph mining has been proposed in this paper to make a paradigm shift in the way of representing the face region, where the face region is represented as a graph of nodes and edges and the gSpan frequent sub-graphs mining algorithm is used to find the frequent sub-structures in the graph database of each emotion. To reduce the number of generated sub-graphs, overlap ratio metric is utilized for this purpose. After encoding the final selected sub-graphs, binary classification is then applied to classify the emotion of the queried input facial image using six levels of classification. Binary cat swarm intelligence is applied within each level of classification to select proper sub-graphs that give the highest accuracy in that level. Different experiments have been conducted using Surrey Audio-Visual Expressed Emotion (SAVEE) database and the final system accuracy was 90.00%. The results show significant accuracy improvements (about 2%) by the proposed system in comparison to current published works in SAVEE database.
  • Analysis of sliding electric contact characteristics in augmented railgun
           based on the combination of contact resistance and sliding friction

    • Abstract: Publication date: Available online 28 December 2019Source: Defence TechnologyAuthor(s): Chunyan Zhu, Baoming Li The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches. As the contact resistance depends not only on the contact state but also on the contact stress and temperature, there are some limitations in analyzing the contact characteristics using only the contact resistance. In this paper, the contact characteristics of the augmented railgun are analyzed by the combination of contact resistance and sliding friction coefficient. Firstly, the theoretical calculation model of the contact resistance and friction coefficient of the augmented electromagnetic railgun is established. Then the contact resistance and friction coefficient are calculated by the measured values of the muzzle voltage, rail current and armature displacement. Finally, the contact characteristics are analyzed according to the features of the waveforms of the contact resistance and the friction coefficient, and the analysis conclusions are verified by experimental rail images. The results showed that: the aluminum melt film gradually formed on the contact surface reduces the contact resistance and the friction coefficient; the wear and erosion of the armature cause deterioration of the contact state; after the transition, the reliability of the sliding contact between the armature and rails decreases, resulting in an increase in contact resistance.
  • A split target detection and tracking algorithm for ballistic missile
           tracking during the re-entry phase

    • Abstract: Publication date: Available online 27 December 2019Source: Defence TechnologyAuthor(s): Muhammad Asad, Sumair Khan, Ihsanullah, Zahid Mehmood, Yifang Shi, Sufyan Ali Memon, Uzair Khan In the re-entry phase of a ballistic missile, decoys can be deployed as a mean to overburden enemy defenses. This results in a single track being split into multiple track-lets. Tracking of these track-lets is a critical task as any miss in the tracking procedure can become a cause of a major threat. The tracking process becomes more complicated in the presence of clutter. The low detection rate is one of the factors that may contribute to increasing the difficulty level in terms of tracking in the cluttered environment. This work introduces a new algorithm for the split event detection and target tracking under the framework of the joint integrated probabilistic data association (JIPDA) algorithm. The proposed algorithm is termed as split event-JIPDA (SE-JIPDA). This work establishes the mathematical foundation for the split target detection and tracking mechanism. The performance analysis is made under different simulation conditions to provide a clear insight into the merits of the proposed algorithm. The performance parameters in these simulations are the root mean square error (RMSE), confirmed true track rate (CTTR) and confirmed split true track rate (CSTTR).
  • An eikonal equation based path planning method using polygon decomposition
           and curve evolution

    • Abstract: Publication date: Available online 24 December 2019Source: Defence TechnologyAuthor(s): Zheng Sun, Zhu-Feng Shao, Hui Li Path planning is a key technique of autonomous navigation for robots, and the velocity field is an important part. Constructing velocity field in a complex workspace is still challenging. In this paper, an inner normal guided segmentation algorithm in a complex polygon is proposed to decompose the complex workspace in this paper. The artificial potential field model based on probability theory is then used to calculate the potential field of the decomposed workspace, and the velocity field is obtained by utilizing the potential field of this workspace. Path optimization is implemented by curve evolution, during which the internal force generated in the smoothing process of the initial path by a mean filter and the external force is obtained from the gradient of the workspace potential field. The parameter selection principle is deduced by analyzing the influence of several parameters on the path length and smoothness. Simulation results show that the designed polygon decomposition algorithm can effectively segment complex workspace and that the path optimization algorithm can shorten and smoothen paths.
  • Integrated guidance and control of guided projectile with multiple
           constraints based on fuzzy adaptive and dynamic surface

    • Abstract: Publication date: Available online 17 December 2019Source: Defence TechnologyAuthor(s): Shang Jiang, Fu-qing Tian, Shi-yan Sun, Wei-ge Liang Based on fuzzy adaptive and dynamic surface (FADS), an integrated guidance and control (IGC) approach was proposed for large caliber naval gun guided projectile, which was robust to target maneuver, canard dynamic characteristics, and multiple constraints, such as impact angle, limited measurement of line of sight (LOS) angle rate and nonlinear saturation of canard deflection. Initially, a strict feedback cascade model of IGC in longitudinal plane was established, and extended state observer (ESO) was designed to estimate LOS angle rate and uncertain disturbances with unknown boundary inside and outside of system, including aerodynamic parameters perturbation, target maneuver and model errors. Secondly, aiming at zeroing LOS angle tracking error and LOS angle rate in finite time, a nonsingular terminal sliding mode (NTSM) was designed with adaptive exponential reaching law. Furthermore, combining with dynamic surface, which prevented the complex differential of virtual control laws, the fuzzy adaptive systems were designed to approximate observation errors of uncertain disturbances and to reduce chatter of control law. Finally, the adaptive Nussbaum gain function was introduced to compensate nonlinear saturation of canard deflection. The LOS angle tracking error and LOS angle rate were convergent in finite time and whole system states were uniform ultimately bounded, rigorously proven by Lyapunov stability theory. Hardware-in-the-loop simulation (HILS) and digital simulation experiments both showed FADS provided guided projectile with good guidance performance while striking targets with different maneuvering forms.
  • Gabor-CNN for object detection based on small samples

    • Abstract: Publication date: Available online 12 December 2019Source: Defence TechnologyAuthor(s): Xiao-dong Hu, Xin-qing Wang, Fan-jie Meng, Xia Hua, Yu-ji Yan, Yu-yang Li, Jing Huang, Xun-lin Jiang Object detection models based on convolutional neural networks (CNN) have achieved state-of-the-art performance by heavily rely on large-scale training samples. They are insufficient when used in specific applications, such as the detection of military objects, as in these instances, a large number of samples is hard to obtain. In order to solve this problem, this paper proposes the use of Gabor-CNN for object detection based on a small number of samples. First of all, a feature extraction convolution kernel library composed of multi-shape Gabor and color Gabor is constructed, and the optimal Gabor convolution kernel group is obtained by means of training and screening, which is convolved with the input image to obtain feature information of objects with strong auxiliary function. Then, the k-means clustering algorithm is adopted to construct several different sizes of anchor boxes, which improves the quality of the regional proposals. We call this regional proposal process the Gabor-assisted Region Proposal Network (Gabor-assisted RPN). Finally, the Deeply-Utilized Feature Pyramid Network (DU-FPN) method is proposed to strengthen the feature expression of objects in the image. A bottom-up and a top-down feature pyramid is constructed in ResNet-50 and feature information of objects is deeply utilized through the transverse connection and integration of features at various scales. Experimental results show that the method proposed in this paper achieves better results than the state-of-art contrast models on data sets with small samples in terms of accuracy and recall rate, and thus has a strong application prospect.
  • Development of cost effective personnel armour through structural

    • Abstract: Publication date: Available online 10 December 2019Source: Defence TechnologyAuthor(s): P. Rama Subba Reddy, T. Sreekantha Reddy, I. Srikanth, Juhi Kushwaha, V. Madhu The objective of the present study is to develop cost effective thermoplastic hybrid laminate using Dyneema® HB50 and Tensylon®HSBD 30A through structural hybridization method. Laminates having 20 mm thickness were fabricated and subjected to 7.62 × 39 mm mild steel core projectile with an impact velocity of 730 ± 10 ms−1. Parameters such as energy absorption, back face deformation and rate of back face deformation were measured as a function of hybridization ratio. It was observed that hybrid laminate with 50:50 ratio (w/w) of Tensylon® and Dyneema® with Tensylon® as front face showed 200% more energy absorption when compared to 100% Tensylon® laminate and showed equal energy absorption as that of expensive 100% Dyneema® laminate. Moreover, hybrid laminate with TD50:50 ratio showed 40% lower in terms of final back face deformation than Dyneema® laminate. Rate of back face deformation was also found to be slow for hybrid laminate as compared to Dyneema® laminate. Dynamic mechanical analysis showed that, Tensylon® laminate has got higher stiffness and lower damping factor than Dyneema® and hybrid laminates. The interface between Tensylon® and Dyneema® layers was found to be separating during the penetration process due to the poor interfacial bonding. Failure behaviour of laminates for different hybridization ratios were studied by sectioning the impacted laminates. It was observed that, the Tensylon® laminate has undergone shear cutting of fibers as major failure mode whereas the hybrid laminate showed shear cutting followed by tensile stretching, fiber pull out and delamination. These inputs are highly useful for body armour applications to design cost effective armour with enhanced performance.
  • Effects of jute fibre content on the mechanical and dynamic mechanical
           properties of the composites in structural applications

    • Abstract: Publication date: Available online 10 December 2019Source: Defence TechnologyAuthor(s): Suhad D. Salman Due to notable characteristics, sustainability concept and environmental issues, hybridisation natural with synthetic fibres to fabricate composites have been rapidly gaining market share in different applications (structural, military, aerospace and automotive vehicles). Compression, tension and fatigue tests of various stacking sequences of plain jute/carbon reinforced (PVB) polyvinyl butyral by hot hydraulic press technique were experimentally conducted. Six types of fabricated composites with various constituents (jute, carbon and their hybrids) were fabricated and tested. Notably, fatigue lifetime of hybrids increases with increasing the carbon content relative to the jute fibre content. On the other hand, Jute composites possess high strain compared to pure carbon composite, which gives an overall improvement in mechanical behaviours. Interestingly, H1 hybrid with Carbon/Jute/Carbon sequences offers similar fatigue stiffness behaviour of H3 hybrid with Carbon/Jute/Carbon/Jute sequences when subjected to cyclic loading. Carbon composite (C) exhibited the highest fatigue resistance, whiles jute composite (J) possessed the highest strain and semi brittle trends in both mechanical and fatigue performance. Results concluded that plain jute fibres could partially replace high-cost synthetic carbon fibres to produce more eco-friendly hybrids to be utilised in different composites industries.
  • Modeling and simulation of bullet-barrel interaction process for the
           damaged gun barrel

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Chao Shen, Ke-dong Zhou, Ye Lu, Jun-song Li In this paper, the influences of bore damage on the bullet-barrel interaction process and the mechanism of how bore damage results in the end of a machine gun barrel's service life were studied, which had seldom been paid attention to in the past several decades. A novel finite element mesh generation method for the damaged barrel and a new transient coupled thermo-mechanical finite element (FE) model, which were based on the damage data obtained through barrel life tests, were developed to simulate the interior ballistics process of a coupled bullet-barrel system. Additionally, user subroutine VUAMP was developed in the FE model in order to take the bullet base pressure brought by propellant gas into account. Good consistency between the simulation results and the experimental results verified the preciseness of the proposed mesh generation method and the FE model. The simulation results show that the increase of bullet's initial disturbance at the muzzle and the variation of its surface morphology caused by bore damage are primarily responsible for the life end of this 12.7 mm machine gun barrel.
  • Meso-mechanical model of concrete under a penetration load

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Cheng Wu, Wenbin Li, Xiaojun Shen The influence of concrete components on projectile penetration is significant. To study the relationship between the equivalent mechanical properties and components of concrete under a penetration load, concrete is simplified as a two-phase composite of coarse aggregate and mortar, and a meso-mechanical model is established, including the equivalent equation of state model, the equivalent confining pressure strength model and the equivalent dynamic tensile strength model, considering shear stress, large deformation and pore compression. Tests of the mechanical properties of mortar, concrete and limestone were conducted; the results show that the equivalent mechanical properties of concrete calculated by the meso-mechanical model are consistent with the test results, and the equivalent mechanical properties of concrete with different volume fractions of coarse aggregate are obtained. Meso-scale and macro-scale numerical simulations of a projectile penetrating into concrete are carried out, the penetration depths obtained by meso-scale and macro-scale numerical simulations are consistent for different volume fractions of coarse aggregate and different velocities of the projectile, which verifies the rationality of the meso-mechanical model.
  • Prediction and optimization of machining forces using oxley's predictive
           theory and RSM approach during machining of WHAs

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Chithajalu Kiran Sagar, Tarun Kumar, Amrita Priyadarshini, Amit Kumar Gupta Tungsten heavy alloys have come up as one of the best alternatives for high density fragmenting devices and armor piercing ammunition. Machining is mandatory for obtaining the final shapes of such kind of ammunitions. However, due to high density and elastic stiffness of WHAs, cutting forces will be higher than for most of the metals and alloys; thus, making the machining operation challenging. The machining variable, namely, cutting force components are significantly influenced by the cutting parameters. This paper makes use of Oxley's predictive analytical model in conjunction with Johnson-Cook constitutive equation to predict forces under different speed and feed combinations during machining of 95 W tungsten heavy alloy. The cutting forces, so predicted by M1, are considered as input data for the optimization of cutting parameters (cutting speed and feed) using Response Surface Method (RSM).
  • Fragmentation behavior of large-caliber PELE impacting RHA plate at low

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Mo-ang Lei, Hai-fu Wang, Qing-bo Yu, Yuan-feng Zheng Impact experiments of large-caliber PELE with various inner-outer diameter ratio perforating RHA plate at low velocity were performed. Experimental results showed the size of perforated holes on plate, average diameter of damage area on witness plate, and number of behind-armor fragments will increase as d/D increasing from 0.72 to 0.84. Expansion and fragmentation of large-caliber PELE in this condition were also numerically studied with ANSYS Autodyn. Then, an analytical model accounting for an additional radial shock wave was presented to predict radial expansion velocity and fragmentation of jacket, as well as an empirical approach to estimate diameter of damage area. Calculation results by these approaches were in good agreement with experiments and numerical simulations. Further discussion revealed that Shock/rarefaction wave interactions behavior varying with inner-outer diameter ratio is an important mechanism resulting in different lateral effect by PELE projectiles with various configurations.
  • Analysis of vibration signal responses on pre induced tunnel defects in
           friction stir welding using wavelet transform and empirical mode

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): J. Rabi, T. Balusamy, R. Raj Jawahar Among many condition-monitoring systems in welding operation, Defect identification is an important method to ensure the precision in finishing operation. Friction stir welding is a solid state welding process used to join two metals without the use of electrode at lower temperatures. The aim of this present work is to identify and localize the tunnel defect in aluminum alloy and measure the distance of the defect zone in the time domain of the vibration signal during Friction stir welding. The vibration signals are captured from the experiments and the burst in the vibration signal is focused in the analysis. A signal-processing scheme is proposed to filter the noise and to measure the dimensional parameters of the defect area. The proposed technique consists of discrete wavelet transform (DWT), which is used to decompose the signal. The enveloping technique is applied on the decomposed zero padded signal. The continuous wavelet transform (CWT) has been implemented on detailed signal followed by a time marginal integration (TMI) of the CWT scalogram. Empirical mode decomposition (EMD) is used to replace the detailing coefficients from DWT with Intrinsic Mode Function (IMF). Statistical parameters such as mean, kurtosis, S.D and crest factor have been extracted from the final filtered signal for validating the defect welds from the control defect free welds. Results produced were found to be that kurtosis is 7.4402 for tunnel defect induced weld and 3.3862 for defect free welds. As the increase in kurtosis value predicts the defect zone impact in the signal. The measurement of the defect zone of the cut 1 (voids) and cut 2 (tunnel grooves) in correlation with the processed signal is found to produce a much redundant results with an error rate of 0.02.
  • Investigating the dynamic mechanical behaviors of polyurea through
           experimentation and modeling

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Hao Wang, Ximin Deng, Haijun Wu, Aiguo Pi, Jinzhu Li, Fenglei Huang Polyurea is widely employed as a protective coating in many fields because of its superior ability to improve the anti-blast and anti-impact capability of structures. In this study, the mechanical properties of polyurea XS-350 were investigated via systematic experimentation over a wide range of strain rates (0.001–7000 s−1) by using an MTS, Instron VHS, and split-Hopkinson bars. The stress-strain behavior of polyurea was obtained for various strain rates, and the effects of strain rate on the primary mechanical properties were analyzed. Additionally, a modified rate-dependent constitutive model is proposed based on the nine-parameter Mooney-Rivlin model. The results show that the stress-strain curves can be divided into three distinct regions: the linear-elastic stage, the highly elastic stage, and an approximate linear region terminating in fracture. The mechanical properties of the polyurea material were found to be highly dependent on the strain rate. Furthermore, a comparison between model predictions and the experimental stress-strain curves demonstrated that the proposed model can characterize the mechanical properties of polyurea over a wide range of strain rates.Graphical abstractImage 1
  • Thermal decomposition of ammonium perchlorate catalyzed with CuO

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Sherif Elbasuney, M. Yehia Ammonium perchlorate (APC) is the most common oxidizer in use for solid rocket propulsion systems. However its initial thermal decomposition is an endothermic process that requires 102.5 J·g−1. This manner involves high activation energy and could render high burning rate regime. This study reports on the sustainable fabrication of CuO nanoparticles as a novel catalyzing agent for APC oxidizer. Colloidal CuO nanoparticles with consistent product quality were fabricated by using hydrothermal processing. TEM micrographs demonstrated mono-dispersed particles of 15 nm particle size. XRD diffractogram demonstrated highly crystalline material. The synthesized colloidal CuO particles were effectively coated with APC particles via co-precipitation by using fast-crash solvent–antisolvent technique. The impact of copper oxide particles on APC thermal behavior has been investigated using DSC and TGA techniques. APC demonstrated an initial endothermic decomposition stage at 242 °C with subsequent two exothermic decomposition stages at 297.8 °C and 452.8 °C respectively. At 1 wt%, copper oxide offered decrease in initial endothermic decomposition stage by 30%. The main outcome of this study is that the two main exothermic decomposition peaks were merged into one single peak with an increase in total heat release by 53%. These novel features can inherit copper oxide particles unique catalyzing ability for advanced highly energetic systems.
  • Study on liquid-filled structure target with shaped charge vertical

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Min Guo, Xu-dong Zu, Xiao-jun Shen, Zheng-xiang Huang Based on the characteristic expanded hole of a shaped charge jet (SCJ) for target penetration and the reflow characteristics of liquids, the liquid-filled structure of a target disturbs the stability of the SCJ acquired in two independent parts. The interference jet speed interval, the escape jet speed interval, and the surplus depth are calculated on the basis of the virtual origin theory. The experimental results, including the velocity of the escaped jet tip and the surplus depth of penetration, are consistent with the theoretical results. Experiments show that the theory can describe the interaction process of the target with a shaped charge jet.
  • FEM analysis and experimental investigation of force and chip formation on
           hot turning of Inconel 625

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Asit Kumar Parida, Kalipada Maity This study investigates the hot machining of Inconel 625 alloy by using flame heating under different machining conditions using finite element analysis (FEM). Turning tests are performed at different cutting speeds and heating temperatures using uncoated carbide insert by DEFORM software. Significant reduction in cutting force and tool wear has achieved at heating conditions compared to room temperature. Highest tool life is achieved at the highest cutting speed and higher heating temperature condition. At heating conditions of the 600 °C continuous chip is formed whereas at room temperature saw-tooth chip formation is observed. A significant agreement is achieved between simulated and experimental cutting forces and chip morphology. The effect of feed rates and depth of cuts are also studied experimentally during turning of Inconel 625 in a systematic manner.
  • Effect of particle gradation of aluminum on the explosion field pressure
           and temperature of RDX-based explosives in vacuum and air atmosphere

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Fan Jiang, Xiao-feng Wang, Ya-feng Huang, Bo Feng, Xuan Tian, Yu-lei Niu, Kun Zhang To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive, an explosion device was developed and used to investigate the detonation pressure and temperature of R1 (Al6) aluminum powder and the aluminum powder particle gradation of R2 (Al6+Al13), R3 (Al6+Al24) and R4 (Al6+Al flake) in a confined space. By using gas chromatography, quantitative analysis and calculations were carried out to analyze the gaseous detonation products. Finally, the reaction ratios of the aluminum powder and the explosion reaction equations were calculated. The results show that in a confined space, the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum. In vacuum, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2, respectively. In air, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3, respectively. R4 (Al6+Al flake) and R3 (Al6+Al24) have relatively higher temperatures after detonation, which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by 10.6% and 8.0%, respectively. In air, the reaction ratio of Al6 aluminum powder can reach as high as 78.16%, and the reaction ratio is slightly reduced after particle gradation. Finally, the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products, which provides a powerful basis for the study of RDX-based explosive reactions.
  • Sonochemically assisted synthesis of nano HMX

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Hema Singh, Nilesh Jahagirdar, Shaibal Banerjee Nanotechnology has played an influential role in improving the energetic content without subsiding the performance of high energy materials in the current era. In this work, HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) nanoparticles were prepared by sonochemically assisted solvent-antisolvent spray technique focussing the reduction in its size so as to improve its energetic properties. In order to fabricate nano HMX various parameters such as different solvents and temperature were investigated. Sonication is one of the strategies recently explored in this regard; so time dependent study of sonication using probe sonicator was performed. It has been postulated that bubble formed during sonication when collapses generate high temperature and many nucleation sites which leads to the formation of uniform spherical particles with small size and fast transition phase. XRD studies depicted phase transformation from α to β as a result of sonication. The TEM images revealed that the rise in the sonication time resulted into decrease in the particle size from 300 to 10 nm. Differential scanning calorimetry (DSC) was employed to determine the heat release of the samples and enhancement in the heat release with the decrease in the particle size. A decrease in the spark sensitivity was observed from 2J (regular HMX) to 50 mJ (nano HMX).Graphical abstractImage 1
  • Adaptive fault-tolerant control based on boundary estimation for space
           robot under joint actuator faults and uncertain parameters

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Rong-Hua Lei, Li Chen Since the joint actuator of the space robot executes the control instructions frequently in the harsh space environment, it is prone to the partial loss of control effectiveness (PLCE) fault. An adaptive fault-tolerant control algorithm is designed for a space robot system with the uncertain parameters and the PLCE actuator faults. The mathematical model of the system is established based on the Lagrange method, and the PLCE actuator fault is described as an effectiveness factor. The lower bound of the effectiveness factors and the upper bound of the uncertain parameters are estimated by an adaptive strategy, and the estimated value is fed back to the control algorithm. Compared with the traditional fault-tolerant algorithms, the proposed algorithm does not need to predetermine the lower bound of the effectiveness factor, hence it is more in line with the actual engineering application. It is proved that the algorithm can guarantee the stability of the closed-loop system based on the Lyapunov function method. The numerical simulation results show that the proposed algorithm can not only compensate for the uncertain parameters, but also can tolerate the PLCE actuator faults effectively, which verifies the effectiveness and superiority of the control scheme.
  • Round robin using the depth of penetration test method on an armour grade

    • Abstract: Publication date: December 2019Source: Defence Technology, Volume 15, Issue 6Author(s): Erik P. Carton, Bernt B. Johnsen, Dennis-Bo Rahbek, Hans Broos, Almar Snippe The depth of penetration (DOP) method is a well-known ballistic test method for characterisation and ranking of ceramic armour materials. The ceramic tile is bonded to a backing material of semi-infinite thickness, and the penetration depth of the projectile gives a measure of the performance of the ceramic. There is, however, an inherent variability in the results from this test method. In this work, the accuracy and the variability of the DOP method has been investigated in a round robin exercise. Six ballistic test centres took part in the exercise. A test protocol was developed, in which the threat type (projectile and impact conditions) and a procedure on how to prepare the targets were specified. The targets consisted of alumina tiles of two different thicknesses that were bonded to polycarbonate backing cubes. Two different 7.62 mm armour piercing projectiles were employed; one with a hard steel core and one with a tungsten carbide core. The projectiles and the other materials all came from single material batches in order to avoid batch-to-batch variations in material properties. These materials were distributed between the ballistic test centres. The test results of the different ballistic test facilities were collected and compared. There was not a lot of variation between the average DOP values obtained at each laboratory, but the variation in penetration depth between shots was high. The consequence of this variation may be less confidence in the test results, and a statistical method was used to evaluate the required number of tests that are sufficient to obtain an average result with high confidence. In most cases, the required number of tests is much higher than what is practically feasible. This work was conducted as part of the European Defence Agency-project CERAMBALL.
  • A comparison of piecewise cubic Hermite interpolating polynomials, cubic
           splines and piecewise linear functions for the approximation of projectile

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): C.A. Rabbath, D. Corriveau Modelling and simulation of projectile flight is at the core of ballistic computer software and is essential to the study of performance of rifles and projectiles in various engagement conditions. An effective and representative numerical model of projectile flight requires a relatively good approximation of the aerodynamics. The aerodynamic coefficients of the projectile model should be described as a series of piecewise polynomial functions of the Mach number that ideally meet the following conditions: they are continuous, differentiable at least once, and have a relatively low degree. The paper provides the steps needed to generate such piecewise polynomial functions using readily available tools, and then compares Piecewise Cubic Hermite Interpolating Polynomial (PCHIP), cubic splines, and piecewise linear functions, and their variant, as potential curve fitting methods to approximate the aerodynamics of a generic small arms projectile. A key contribution of the paper is the application of PCHIP to the approximation of projectile aerodynamics, and its evaluation against a set of criteria. Finally, the paper provides a baseline assessment of the impact of the polynomial functions on flight trajectory predictions obtained with 6-degree-of-freedom simulations of a generic projectile.
  • Comparative analysis of the effects of gunpowder and plasma ignition in
           closed vessel tests

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Radoslaw Trebinski, Zbigniew Leciejewski, Zbigniew Surma, Jakub Michalski This paper presents the results of a comparative investigation into the effects of the ignition method on the ballistic properties of a single-base gun propellant, as determined via closed vessel tests. Conventional gunpowder ignition and plasma jet ignition methods were used, and differences in the ignition time were analysed. The influence of the ignition method on the dynamic vivacity is discussed. It is shown that this influence is significant in the first phase of the combustion process, and with respect to the low values of the loading density. In the second phase of the combustion process, and for large values of the loading density, the dynamic vivacity plots for the two ignition methods converge. Regarding the burning law, close values of the exponent were obtained for the two ignition methods. The dynamic vivacity plots determined for plasma ignition reveal stronger dependence on the loading density than those determined for gunpowder ignition. The conclusion is that plasma ignition is not a solution to the problems inherent to the process of determining the ballistic properties of propellants, which results in deviation of the burning process from the geometric burning law.
  • Numerical simulation on the pressure wave in a 30 mm
           electrothermal-chemical gun with the discharge rod plasma generator

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Yan-jie Ni, Yong Jin, Gang Wan, Bao-ming Li An axisymmetric two-dimensional (2D) internal ballistic model including the transient burning rate law is used to simulate the 30 mm electrothermal-chemical (ETC) launch with the discharge rod plasma generator (DRPG). The relationship between the pressure wave and the initial parameters, such as input electric power, discharging timing sequence, loading density and propellant web thickness, is researched through the change of initial parameters in the model. In the condition of synchronous discharging, the maximum of the pressure wave can be controlled while the ratio of the input electric energy to the propellant chemical energy (electric energy ratio) is less than 0.11. If the electric energy ratio is larger than 0.11, the maximum of the pressure wave increases rapidly with the electric energy ratio. With the increasing of the electric energy ratio, the change of the first negative amplitude value can be ignored. In the condition of timing sequence discharging, the allowed input electric energy ratio to control the pressure wave is proportional to the current pulse duration. At the high electric energy ratio, the maximum of the pressure wave is inverse proportional to the current pulse duration. The pressure wave increases with the increasing of the loading density. But the allowed electric energy ratio to control the pressure wave and the variation trend of the first negative amplitude wave value doesn't change. During the discharging of the DRPG, the influence of changing propellant web thickness in ETC launch can be ignored.
  • Influence of multiple structural parameters on interior ballistics based
           on orthogonal test methods

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Chao-bin Hu, Xiao-bing Zhang Influence of multiple structural parameters on the performance of a gun launch system driven by high-pressure reactive gases is important for structural design and performance adjustment. A coupled lumped parameter model was utilized to predict the propellant combustion, and a dynamic finite element method was applied to approximate the mechanical interactions between the projectile and the barrel. The combustion and the mechanical interactions were coupled through a user subroutine interface in ABAQUS. The correctness and the capability of the finite element approximations in capturing small structural changes were validated by comparing predicted resistance with experiments. Based on the coupled model, the influence of structural parameters of a medium-caliber gun on the system performance was investigated. In order to reduce the research costs, orthogonal tests were designed to investigate the comprehensive effects of the parameters. According to statistical analysis, the important order of the structural parameters on the launching process was obtained. The results indicate that the influence of the width of the rotating band stands out among the studied parameters in the gun. The work provides a method to investigate the influence of multiple parameters on system performance and gives guidance for controlling the system performance.
  • Design and manufacture of a 100 kA coaxial pulsed power cable for plasma
           generator and PPS in ETC guns

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Yong Jin, Zhen-xiao Li, Yan-jie Ni, Xiao-ya Gao, Gang Wan, Chun-xia Yang, Bao-ming Li Based on our previous pulsed current and internal overvoltage test data and the experience of common commercial high power cables, a 100 kA coaxial pulsed power cable is designed and manufactured to adapt the coaxial electric energy breech transmission between the plasma generator and the pulsed power supply (PPS) in electrothermal-chemical (ETC) guns. The index parameters are analyzed and determined. Semi-conductor layers and a shield stiffener are introduced to prevent the deformation and burst of the pulsed power cable structurally. The semi-conductor layer can eliminate the air gap and balance the electric field in the cable. The shield stiffener can multiply the mechanical strength to restrain the strong electrodynamic force produced by the core dislocation of the outer conductor. The multi-coupling of electromagnetic field, stress field and thermal field analysis are established to assist in aided design of electrical strength, mechanical strength and temperature rise characteristics. Both a DC voltage withstand test and pulsed discharge tests are introduced to verify and inspect the performance and dynamic response of the pulsed power cable. The 25 kV/5min DC voltage withstand test result shows that the sample leakage current is nearly 3 μA and no abnormal phenomena of the pulsed power cable sample occurred. The pulsed discharge tests show that the sample can sustain the 100 kA peak current. Furthermore, this 100 kA coaxial pulsed power cable can satisfy the ETC test requirements.
  • A prediction method for the performance of a low-recoil gun with front

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Cheng Cheng, Chong Wang, Xiaobing Zhang One of the greatest challenges in the design of a gun is to balance muzzle velocity and recoil, especially for guns on aircrafts and deployable vehicles. To resolve the conflict between gun power and recoil force, a concept of rarefaction wave gun (RAVEN) was proposed to significantly reduce the weapon recoil and the heat in barrel, while minimally reducing the muzzle velocity. The main principle of RAVEN is that the rarefaction wave will not reach the projectile base until the muzzle by delaying the venting time of an expansion nozzle at the breech. Developed on the RAVEN principle, the purpose of this paper is to provide an engineering method for predicting the performance of a low-recoil gun with front nozzle. First, a two-dimensional two-phase flow model of interior ballistic during the RAVEN firing cycle was established. Numerical simulation results were compared with the published data to validate the reliability and accuracy. Next, the effects of the vent opening times and locations were investigated to determine the influence rules on the performance of the RAVEN with front nozzle. Then according to the results above, simple nonlinear fitting formulas were provided to explain how the muzzle velocity and the recoil force change with the vent opening time and location. Finally, a better vent venting opening time corresponding to the vent location was proposed. The findings should make an important contribution to the field of engineering applications of the RAVEN.
  • Effect of the firing position on aiming error and probability of hit

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): D. Corriveau, C.A. Rabbath, A. Goudreau Sources of dispersions that contribute to delivery error and reduce the soldier performance in terms of hit probability are numerous. In order to improve the warfighter performance, the source of the errors contributing to the inaccuracy and dispersion of the weapon systems must be understood. They include ammunition dispersion error, gun dispersion, aerodynamic jump and the aiming error. The aiming error or gun pointing error is defined as the angle between the gun muzzle at the instant the trigger is pulled and the line of fire that corresponds to the intendent aim point. This is a round-to-round error. In weapons systems that include the rifle, the ammunition, a sight and a gunner, the aiming error was shown to be the single most important source of dispersion for the regular infantryman. In other words, for the general purpose rifle weapon system, the weak link is often the human. In order to verify and quantify this assertion, an experimental investigation was carried out to determine the aiming error associated with general purpose rifle fired by infantryman. The aiming error was evaluated for various firing positions and scenarios using infantryman for ranges varying between 100 m and 500 m. The results show that the aiming error is the main contributor to dispersion for the general purpose rifle fired by a non-specialized infantryman. The aiming error induced dispersion for unstressed and rested gunners is shown to be at best equivalent to that of the weapon fired from a bench rest by a marksman.
  • Analysis of in-bore balloting and control of jump variability

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Satoru Shoji The variability of projectile jump is the long-term issue to improve weapon accuracy. Nowadays we have many simulation codes to predict Jump. However, these codes cannot explain explicitly how the variability of jump arises. The aims of this paper are, 1) to give fundamental explanations for the variability of Jump, and 2) to offer design factors to make the variability of Jump less. The model presented here was formulated in accordance with the transition of the system in reverse way commencing from the target impact stage to the chambering stage. Objects of the simulation are generic 120 mm smooth bore and long rod system which are extremely simplified to the vibration of tube, the spring effect by sabot, and the free-ends beam of penetrator. Parametric calculations clarified that high Jump-variability is generated only when the last rebound is on the muzzle line. This particular state of rebound is achieved by many combinations of input-variable. Guide map named JV-Chart is proposed to show the high Jump-variability zone.
  • Research on momentum transfer in simple railgun

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Yingtao Xu, Bo Tang, Baoming Li In this paper, the momentum conservation equation in the longitudinal direction for simple railgun was deduced. Then, a three-dimensional model was established and the finite element method was utilized to simulate the problem. Based on the simulation, some results such as the surface force on the electromagnetic field, the electromagnetic force on the conductor in the longitudinal direction were obtained. Besides, the surface force density on different longitudinal section of railgun was analyzed and discussed in details. The results showed that the momentum of the railgun system was conserved when the surface force of the electromagnetic field was contained. Moreover, large amount of longitudinal force was transmitted to the breech by the electromagnetic field in the form of surface force. The exact position and distribution of recoil were related to the current input device.
  • 31st International Symposium on Ballistics, Hyderabad, India, 4–8
           November 2019

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s):
  • Aerodynamic and trajectory characteristics of a typical mortar projectile
           with a deflectable nose

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Yu-ming Ren, Shu-shan Wang, Jing-wei Li, Xun-cheng Guo, Yue-song Mei Deflectable nose control is a new trajectory correction method. In this paper, the aerodynamic and trajectory characteristics of a typical mortar projectile with a deflectable nose are investigated with respect to its flight conditions. Using the method of wind tunnel testing, the aerodynamic coefficients of four kinds of mortar models were measured under the conditions of different angles of attack from −10° to 10° and Mach numbers from 0.3 to 0.9. Based on the aerodynamic coefficients, the trajectory ranges at different nose deflection angles and times were calculated. Furthermore, a trajectory optimization was performed by reducing the static margin. The results and discussions show that the nose deflection provided limited lift, while the pitching moment varied significantly. The mortar obtained the extended flight range and trajectory correction ability with nose deflection.
  • Firm embedding behavior of annular grooved projectiles impacting ductile
           metal targets

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Qi Huang, Shun-shan Feng, Xu-ke Lan, Chao-nan Chen, Yong-xiang Dong, Tong Zhou Annular grooved projectiles (AGPs) have drawn ongoing concerns as an advanced penetrator for their excellent anti-rebound capability in impacting metal plates. They could become embedded solidly in the target surface during low-velocity impact. In this investigation, the firm embedding behavior of AGP was observed by impact experiments. Corresponding numerical simulations provided a better understanding of this process. Experimental and numerical results indicated that the firm embedding behavior of AGP was mainly due to the filling-material in the groove rather than the friction between the projectile and target, unlike traditional shape such as conical projectile. According to observation, firm embedding process can generally be subdivided into four stages: initial-cratering stage, groove-filling stage, filling-material failure stage and rebound vibration stage. Moreover, the damage mechanics of target material around crater was obtained through microscopic tests. A comparison of the cross-sectional figures between the experiment and simulation proved that the analysis and the proposed method were reasonable and feasible, which further demonstrated that the firm embedding behavior has application potential in new concept warheads.
  • Re-visiting the mass-flux model for Explosive Reactive Armor and the
           effect of plate thickness

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): M. Mayseless, S. Friling, L. Misiuk Explosive Reactive Armor was originally modeled under the assumption that the plates in the cassettes were very thin. Hence their thickness could be ignored, and the thicknesses of the plates were considered only based on their areal mass density. In particular, it was assumed that the jet-plate interaction was controlled by the plates to jet-mass-flux ratio criteria for a specific jet velocity and diameter. In the present study, we extended this analysis, examining the effect of the variation of the mass-flux along the jet on the disruption effect by the two plates. In addition, we examined the thickness effect of the plates on the plate's effectiveness, replacing the steel plates by low-density materials like aluminum and polycarbonate. The mass-flux model was adjusted to account for the plate-thickness effect. It was found that increasing the thickness of the plate, keeping the areal weight unchanged, slightly increases the overall effectiveness of the cassette, in particular by the forward moving plate interacting with the center and the slow parts of the jet.
  • Deformation, fragmentation and acceleration of a controlled fragmentation
           charge casing

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Andreas Helte, Olof Andersson, Patrik Lundberg Two different finite element software, LS-DYNA and Impetus, have been evaluated to test their ability to predict the deformation, fragmentation and acceleration of a controlled fragmentation charge casing. The general-purpose program LS-DYNA was used with a multi-material ALE formulation and a mass-preserving erosion criterion coupled to a Johnson-Cook fracture criterion. In the Impetus simulations, a third order Lagrangian element formulation was used for the casing and a node-splitting element erosion treatment coupled to a Cockcroft-Latham failure criterion was used to describe casing fracture. The high-explosive gases were described by a discrete particle formalism.In order to acquire data to validate our computational tools and constitutive models, a series of experiments have been performed using a laboratory charge with an internal grooved casing. In the test series, the charge geometry was fixed except that the groove depth were varied from very shallow to very deep resulting in different deformation patterns, fracture modes and terminal velocities. Various diagnostic tools captured the different stages of the expansion and fragmentation of the casing. A high-speed framing camera depicted the deformation pattern before fragmentation and was used to determine the moment when the casing failed. Three different complementary techniques were used to follow the acceleration of the fragments; a Photon Doppler velocimetry to determine the initial acceleration of the casing, double exposed radiographs to estimate the fragment velocity after break-up and a high-speed video to determine the terminal velocity of the fragment after leaving the fireball. In addition, the fragments were soft recovered in a set of sawdust pit tests and their final shape and weight were measured. A SEM was used to characterise the fracture surfaces and to determine the modus of fracture (tensile or shear failure).Comparisons to experiments show that both software can predict the change in deformation behaviour when the groove depth increases, from tangential necking for shallow grooves to radial punching for deep groves. Both software could also reasonable well predict the acceleration of the fragments, though both overestimates the terminal velocity for the charge with the deepest grooves.
  • Bore-center annular shaped charges with different liner materials
           penetrating into steel targets

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Wen-long Xu, Cheng Wang, Jian-ming Yuan, Tao Deng The bore-center annular shaped charge (BCASC) is a new type of shaped charge which can generate a larger-diameter hole in steel targets than classical shaped charges. In this paper, the influence of three liner materials, i.e. molybdenum, nickel and copper, on BCASC formation and penetrating into steel targets was investigated by experiment and numerical simulation. The simulation results were well consistent with the experimental results. This study showed that, at 0.50D standoff distance, the axial velocity of the molybdenum projectile was lower than that of the nickel and copper projectiles. The nickel and copper projectiles had almost the same head velocity. The absolute values of the radial velocity of the molybdenum projectile head was lower than that of the nickel and copper projectiles. However, at 0.75D standoff distance, the absolute values of the radial velocity of the molybdenum projectile head became much greater than that of the nickel and copper projectile heads. The projectile formed by BCASC with the molybdenum liner had the highest penetration depth of 61.5 mm, which was 10.0% and 21.3% higher than that generated by the copper and nickel projectiles.
  • Investigation on the influence of the initial RDX crystal size on the
           performance of shaped charge warheads

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): F. Majiet, F.J. Mostert Copper lined wave shaped shaped charges of particular design and liner metallurgy were used to investigate the effect of explosive crystal size on the resultant shaped charge jet parameters. Composition A3 with RDX of three different average crystal sizes, i.e. 30 μm, 100 μm and 300 μm were used in the investigation. All other parameters in the charge were kept constant and in particular, care was given to obtain consistent dimensional quality and liner microstructure, in order to prohibit the variation of other parameters. Specific flash-X-ray diagnostics were used in field tests to obtain the jet parameters from multiple firings of similar charges. It is found that the varying crystal size of the RDX has a marginal influence in the total jet length of the jets. However, it is also found that there is less variation between firings in the jet parameters for jets from the charges loaded with the crystal size of 100 μm.
  • Experimental studies of explosion energy output with different igniter

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Heyang Xu, Weibing Li, Wenbin Li, Yajun Wang For study the energy output law of cylindrical charge with shell induced by different input energies, four different black powder masses were selected to ignite the main charge. Fragmentation degree of the shell was qualitatively analyzed by the area of holes on the witness plate and the recovered fragments mass. Through theoretical analysis, established the functional relationship between the average mass of fragments and the relative energy output of warhead, obtained how the relative energy output of charge changed with different initial energy input. The results showed that the change of input energy could lead to obvious variation in fragment characteristics, and could also control the output of charge. When the igniter mass increases from 1.55 g to 5.00 g, the relative energy output of the charge increases by 26.28%. Excessive initial input energy will destroy the shell confine in advance, resulting in a decrease in the relative energy output of charge.
  • Modeling of the whole process of shock wave overpressure of free-field air

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Zai-qing Xue, Shunping Li, Chun-liang Xin, Li-ping Shi, Hong-bin Wu The waveform of the explosion shock wave under free-field air explosion is an extremely complex problem. It is generally considered that the waveform consists of overpressure peak, positive pressure zone and negative pressure zone. Most of current practice usually considers only the positive pressure. Many empirical relations are available to predict overpressure peak, the positive pressure action time and pressure decay law. However, there are few models that can predict the whole waveform. The whole process of explosion shock wave overpressure, which was expressed as the product of the three factor functions of peak, attenuation and oscillation, was proposed in the present work. According to the principle of explosion similarity, the scaled parameters were introduced and the empirical formula was absorbed to form a mathematical model of shock wave overpressure. Parametric numerical simulations of free-field air explosions were conducted. By experimental verification of the AUTODYN numerical method and comparing the analytical and simulated curves, the model is proved to be accurate to calculate the shock wave overpressure under free-field air explosion. In addition, through the model the shock wave overpressure at different time and distance can be displayed in three dimensions. The model makes the time needed for theoretical calculation much less than that for numerical simulation.
  • Analysis of global momentum transfer due to buried mine detonation

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): N. Heider, V. Denefeld, H. Aurich The emergence of improvised explosive devices (IED) significantly extended the spectrum of possible threat mechanisms to military vehicles and their occupants. Especially buried high explosive (HE) charges lead to new and originally not investigated loading conditions during their detonation. It is the interaction of the embedding geomaterial with the detonation products that leads to a strongly increased global impulse transfer on the vehicle with following high accelerations on the vehicle occupant. This paper presents a comprehensive approach for the analysis of occupant loading. In a first step, we present the so called ring technology which allows the experimental determination of the locally resolved specific impulse distribution on a vehicle floor due to buried charge detonation. A complementary method is the use of scaled model vehicles that allows the determination of global vehicle loading parameters such as jump height or vehicle accelerations. Both techniques were used to study the influence of burial conditions as burial depth, embedding material or water content on the impulse transfer onto the vehicle. These experimental data are used to validate material models for the embedding sand or gravel materials. This validated material description is the basis for numerical simulation models used in the assessment of occupant safety. In the last step, we present a simulation model for a generic military vehicle including a Hybrid III occupant dummy that is used for the determination of biomechanical occupant exposure levels. Typical occupant loadings are evaluated and correlated with burial conditions as HE mass and global momentum transfer.
  • Design optimization for a launching system with novel structure

    • Abstract: Publication date: October 2019Source: Defence Technology, Volume 15, Issue 5Author(s): Run-duo Cao, Xiao-bing Zhang A launching system with novel structure using optimization method is investigated to improve the muzzle velocity of guns in this article. This system has two tandem chambers of which the front one is ignited first and the other is ignited after a while. The launching process of this novel system is modelled and a series of different schemes are simulated, to discover the interior ballistic performance of this novel launching system. In order to obtain the optimal loading conditions, an optimization model combined with the combustion model is established. The optimal schemes can improve the muzzle velocity by 20.6% without changing the parameters of barrel. It means that this novel launch system could improve the interior ballistics performance significantly and it still has considerable potential to be ameliorated.
  • Magnetic, thermal stability and dynamic mechanical properties of beta
           isotactic polypropylene/natural rubber blends reinforced by NiZn ferrite

    • Abstract: Publication date: Available online 11 March 2019Source: Defence TechnologyAuthor(s): Lih-Jiun Yu, Sahrim Hj Ahmad, Ing Kong, Mouad A. Tarawneh, Shamsul Bahri Bin Abd Razak, Elango Natarajan, Chun Kit Ang The dispersion of magnetic nanoparticles in matrix is crucial to ensure optimum performance of the composite. The difficulty level of achieving good dispersion is further increase when a multi-phases of matrix is present. A pre-coating technique of magnetic nanoparticles with polypropylene using ball-mill prior to melt-blending process was employed to prepare a multi-phases thermoplastic natural rubber composite. The effect of filler loading (2 wt%-10 wt%) on morphology, structure, magnetic properties, thermal stability and dynamic mechanical properties of the composites were investigated. It was found that the NiZn ferrite nanoparticles act as nucleating agent to form beta isostatic polypropylene thermoplastic composites. The composites' magnetic properties are directly dependent on the filler concentration. The dispersion of magnetic fillers in polymer matrix plays role in affecting the magnetic properties and thermal stability. The preference of filler to locate at amorphous phase has distorted the chain orientation of natural rubber and polypropylene. Hence, the polymorphism and crystallinity of the matrix varied as the filler loading increased, affecting the dynamic mechanical properties. It was found that 8 wt% NiZn nanocomposite exhibits highest E’ and tanδ, indicating the dynamic mechanical properties of NiZn nanocomposite are affected by β-phase degree.
  • Advances in phase stabilization techniques of AN using KDN and other
           chemical compounds for preparing green oxidizers

    • Abstract: Publication date: Available online 10 March 2019Source: Defence TechnologyAuthor(s): Pratim Kumar Research and development of green oxidizers and green fuels as a possible replacement for ammonium perchlorate (NH4ClO4, AP) and hydrazine (N2H4) respectively has been increased considerably in the recent years. AP and hydrazine are the oxidizer and fuel entities, and used in solid and liquid rocket motors respectively. AP is highly toxic and led to adverse health effects, while hydrazine is carcinogenic in nature. AP is in use from the last several decades for rocket and space shuttle propulsion, while hydrazine is used in upper stage liquid propelled rocket motors. It's a tough task to replace AP with the currently available green oxidizers; since their ballistic properties are weaker when compared to AP and also they can't be successfully deployed in a solid rocket motor at present. Some important available solid green oxidizers are ammonium nitrate (AN), ammonium dinitramide (ADN), hydroxyl ammonium nitrate (HAN), and hydrazinium nitroformate (HNF). However, AN is one of the cheap and readily available oxidizer, and has great potential to use in solid/ liquid rocket motors. Tremendous progress has been envisaged till now, and more progress will be there in the coming future over the development of AN based green energetic materials (GEM's). A concise overview has been presented over the development of phase stabilized ammonium nitrate (PSAN) and AN/KDN based green oxidizers in the present review paper.
  • Low velocity impact studies of E-glass/epoxy composite laminates at
           different thicknesses and temperatures

    • Abstract: Publication date: Available online 23 February 2019Source: Defence TechnologyAuthor(s): T. Sreekantha Reddy, P. Rama Subba Reddy, Vemuri Madhu Low velocity impact experiments were carried out on E-glass/epoxy composite laminates having varying thicknesses at sub zero and elevated temperatures using hemi spherical steel impactor of 16 mm diameter with impact energies in the rage of 50–150 J. The performance of the laminates was assessed in terms of energy absorption, maximum displacement, peak force and failure behaviour. Results indicated that the effect of temperature on energy absorption of the laminate is negligible although the laminates are embrittling at sub zero temperatures. However it has influence on failure behaviour and displacement. Peak force has increased linearly with increase in laminate thickness from 5 to 10 mm. However it got reduced by 25% when temperature was increased from −20 °C to 100 °C. Based on experimental results, laminate perforation energies were predicted using curve fitting equations. Statistical analysis was carried out using Taguchi method to identify the global effects of various parameters on laminate performance and confirmed that the laminate thickness has significant influence as compared to temperature, for the studied range.
  • A novel non-separation opening scheme of front cover for rocket launch

    • Abstract: Publication date: Available online 24 January 2019Source: Defence TechnologyAuthor(s): Ce Zhang, Xin Zhao, Zonglai Mo, Zhuoyu Guo, Jun Li In view of that existing opening technologies of front cover for rocket launch canister have disadvantages such as causing damage on the ground equipment, not being reused and easily broken. A novel reusable non-separation spring-driven opening scheme is proposed to achieve rapid and reliable opening of the front cover. The mathematical model of the opening process of the front cover is established by the rigid body dynamics theory. To establish a response surface model to optimize the opening scheme, three main influencing factors of the opening process are obtained through the designed experiments, including the pre-compression, the stiffness of the thrust spring, and the thrust spring force arm length. In addition, the prescribed kinematic law was taken as constraint, and the smaller thrust spring preliminary pressure and angular velocity was taken as optimization expectations. The results show that the opening scheme meets the design requirements on opening process well. It also shows that the optimized scheme can reduce the kinetic energy of the front cover, and the impact on the canister effectively, achieving a reliable and rapid opening of the front cover.
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