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International Journal of Structural Integrity
Number of Followers: 2  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1757-9864
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  • Fuzzy optimization design-based multi-level response surface of bogie
           frame
    • Pages: 134 - 148
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 134-148, April 2019.
      Purpose In a structural optimization design-based single-level response surface, the number of optimal variables is too much, which not only increases the number of experiment times, but also reduces the fitting accuracy of the response surface. In addition, the uncertainty of the optimal variables and their boundary conditions makes the optimal solution difficult to obtain. The purpose of this paper is to propose a method of fuzzy optimization design-based multi-level response surface to deal with the problem. Design/methodology/approach The main optimal variables are determined by Monte Carlo simulation, and are classified into four levels according to their sensitivity. The linear membership function and the optimal level cut set method are applied to deal with the uncertainties of optimal variables and their boundary conditions, as well as the non-fuzzy processing is carried out. Based on this, the response surface function of the first-level design variables is established based on the design of experiments. A combinatorial optimization algorithm is developed to compute the optimal solution of the response surface function and bring the optimal solution into the calculation of the next level response surface, and so on. The objective value of the fourth-level response surface is an optimal solution under the optimal design variables combination. Findings The results show that the proposed method is superior to the traditional method in computational efficiency and accuracy, and improves 50.7 and 5.3 percent, respectively. Originality/value Most of the previous work on optimization was based on single-level response surface and single optimization algorithm, without considering the uncertainty of design variables. There are very few studies which discuss the optimization efficiency and accuracy of multiple design variables. This research illustrates the importance of uncertainty factors and hierarchical surrogate models for multi-variable optimization design.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-02-08T02:23:37Z
      DOI: 10.1108/IJSI-10-2018-0062
       
  • Strengthening of Al-4.5%Cu alloy with the addition of Silicon Carbide and
           Bamboo Leaf Ash
    • Pages: 149 - 161
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 149-161, April 2019.
      Purpose The purpose of this paper is to determine the use of BLA along with SiC as economical reinforcements to enhance the mechanical behavior of hybrid composite. The purpose of this research is the development of cost-effective aluminum hybrid metal matrix composites. Design/methodology/approach The present research work investigation evaluated the mechanical properties of Al-4.5%Cu alloy, Al-4.5Cu/10SiC, Al-4.5Cu/10SiC/2BLA and Al-4.5Cu/10SiC/4BLA composites by the Stir casting method. The fabricated composites were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and hardness and tensile test. Findings The microstructure modification with the addition of reinforcement particles in the matrix alloy and clear interface in between matrix and particles are observed. The density of the composite increased with the addition of SiC and decreased with the addition of BLA in comparison with that of matrix alloy. The hardness and tensile strength of the single-reinforced composite and hybrid composites improved with the addition of reinforcement particles. The strengthening of composites was due to load-bearing capacity of reinforcement particles over the matrix alloy and increased dislocation density of composites materials. The tensile failure mechanism of the composites is reveled with SEM analysis. Practical implications The papers reports the development of cost-effective and light weight aluminum hybrid composites with remarkable enhancement in the mechanical and tribological properties with the addition of BLA as economical reinforcement along with SiC. Originality/value The density, hardness and tensile values of fabricated aluminium composites were presented in this paper for the use in the engineering applications where the weight and cost are consider as a primary factors.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-03-14T11:08:55Z
      DOI: 10.1108/IJSI-03-2018-0018
       
  • Parametric optimization of friction stir welding process for marine grade
           aluminum alloy
    • Pages: 162 - 175
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 162-175, April 2019.
      Purpose The purpose of this paper is to deal with the experimental data related to the friction stir welding (FSW) of marine grade Al-Mg4.2 alloy. Mathematical models are developed to study the individual and interaction effects of input variables on the performance characteristics of joints. FSW parameters are optimized to maximize the yield strength and weld nugget microhardness of the welded joints. Design/methodology/approach Response surface methodology is applied to establish the mathematical relationship between six input factors, namely, tool rotational speed, transverse speed, tool shoulder diameter, tool material hardness, tilt angle and pin profile; and two response variables, namely, yield strength and weld nugget microhardness. Six factors–five-level rotatable central composite matrix is used for the design of experiments. The quadratic model is used, as suggested by the design expert software, to express the response parameters as a function of investigated input parameters. The competence of the developed models is verified through analysis of variance. Findings The present investigation clearly indicates that the studied input factors have a significant effect on the quality of the joints. The optimal combination of input factors is determined to achieve the desired responses. Originality/value This paper teems a new look on tensile and hardness properties of Al-Mg4.2 joints by relating the microstructure, fractrographs and grains distribution with the dynamic recrystallization and plasticized material movement during the FSW process. The outcome of this research will help in seizing the opportunities of joining Al-Mg4.2 alloy using FSW, in the offshore and marine applications.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-03-14T11:58:29Z
      DOI: 10.1108/IJSI-01-2018-0007
       
  • Physical seismic vulnerability assessment of neighborhood emphasizing on
           critical land uses
    • Pages: 176 - 187
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 176-187, April 2019.
      Purpose The purpose of this paper is to identify the vulnerable factors in the neighborhood and vulnerability assessment of residential, medical center, school buildings, the road networks and the green spaces as vital and critical land uses to get general estimation of the situation for risk reduction planning. Design/methodology/approach Seismic vulnerability assessment of buildings was performed using the rapid visual screening data collection form of FEMA P 154 (2015). The assessment of the road was carried out using an empirical model, and the condition of the green spaces was assessed complying with standards using GIS. Findings The results of research indicated that about 37 percent of selected residential buildings, 81.08 percent of schools and two health care centers are likely to be vulnerable to earthquake. Originality/value Based on the results of this study, many of the structures should be further evaluated. Strengthening of poor-resistant elements of the roads is recommended and must be in order. Although the green spaces are well distributed in the neighborhood, they are ill-equipped of necessary facilities and their development is also recommended.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-02-11T12:37:00Z
      DOI: 10.1108/IJSI-03-2018-0019
       
  • Flexural capacity of bi-directional GFRP strengthened RC beams with end
           anchorages
    • Pages: 188 - 207
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 188-207, April 2019.
      Purpose The purpose of this paper is to present the results of experimental and theoretical studies on the flexural capacity of reinforced concrete (RC) beams strengthened using externally bonded bi-directional glass fibre reinforced polymer (GFRP) composites and different end anchorage systems. Design/methodology/approach A series of nine RC beams with a length of 1,600 mm and a cross-section of 200 mm depth and 100 mm width were prepared and externally strengthened in flexure with bi-directional GFRP composites. These strengthened beams were anchored with three different end anchorage systems namely closed GFRP wraps, GFRP U-wraps and mechanical anchors. All these beams were tested with four-point bending system up to failure. The experimental results are compared with the theoretical results obtained using the relevant design guidelines. Findings The experimental results demonstrate a significant increase in the flexural performance of the GFRP strengthened beams with regard to the ultimate load carrying capacity and stiffness. The results also show that GFRP strengthened beams without end anchorages experienced intermediate concrete debonding failure at the GFRP plate end, whereas all the GFRP strengthened beams with different end anchorage systems failed in rupture of GFRP with concrete crushing. The theoretical results revealed no significant difference among the relevant design guidelines with regard to the predicted ultimate moment capacities of the bi-directional GFRP strengthened RC beams. However, the results show that ACI Committee 440 Report (2008) design recommendation provides reasonably acceptable predictions for the ultimate moment capacities of the tested beams strengthened externally with bi-directional GFRP reinforcement followed by FIB Bulletin 14 (2001) and eventually by JSCE (1997). Originality/value The research work presented in this manuscript is authentic and could contribute to the understanding of the overall behaviour of RC beams strengthened with FRP and different end anchorage systems under flexural loading.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-02-13T12:01:52Z
      DOI: 10.1108/IJSI-04-2018-0021
       
  • Approach to establish a hybrid intelligent model for crack diagnosis in a
           fix-hinge beam structure
    • Pages: 208 - 229
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 208-229, April 2019.
      Purpose With the development of research toward damage detection in structural elements, the use of artificial intelligent methods for crack detection plays a vital role in solving the crack-related problems. The purpose of this paper is to establish a methodology that can detect and analyze crack development in a beam structure subjected to transverse free vibration. Design/methodology/approach Hybrid intelligent systems have acquired their own distinction as a potential problem-solving methodology adopted by researchers and scientists. It can be applied in many areas like science, technology, business and commerce. There have been the efforts by researchers in the recent past to combine the individual artificial intelligent techniques in parallel to generate optimal solutions for the problems. So it is an innovative effort to develop a strong computationally intelligent hybrid system based on different combinations of available artificial intelligence (AI) techniques. Findings In the present research, an integration of different AI techniques has been tested for accuracy. Theoretical, numerical and experimental investigations have been carried out using a fix-hinge aluminum beam of specified dimension in the presence and absence of cracks. The paper also gives an insight into the comparison of relative crack locations and crack depths obtained from numerical and experimental results with that of the results of the hybrid intelligent model and found to be in good agreement. Originality/value The paper covers the work to verify the accuracy of hybrid controllers in a fix-hinge beam which is very rare to find in the available literature. To overcome the limitations of standalone AI techniques, a hybrid methodology has been adopted. The output results for crack location and crack depth have been compared with experimental results, and the deviation of results is found to be within the satisfactory limit.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-02-11T12:37:05Z
      DOI: 10.1108/IJSI-05-2018-0029
       
  • The effects of residual stresses and strains on lateral-torsional buckling
           behavior of cold-formed steel channel and built-up I-sections beams
    • Pages: 230 - 243
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 230-243, April 2019.
      Purpose The purpose of this paper is to focus on the influences of residual stresses which were induced during roll-forming sections on lateral-torsional buckling of thin-walled cold-formed steel channel and built-up I-sections beams. Built-up I section is made up of two back-to-back cold-formed channel beams. In this direction, at the primary stage, the roll-forming process of a channel section was simulated in ABAQUS environment and the accuracy of the result was verified with those existing experiments. Residual stresses and strains in both longitudinal and circumferential transverse directions were extracted and considered in the lateral-torsional buckling analysis under uniform end moments. The contribution of the current research is devoted to the numerical simulation of the rolling process in ABAQUS software enabling to restore the remaining stresses and strains for the buckling analysis in the identical software. The results showed that the residual stresses decrease considerably the lateral-torsional buckling strength as they have a major impact on short-span beams for channel sections and larger span for built-up I sections. The obtained moment capacity from the buckling analysis was compared to the predictions by American Iron and Steel Institute design code and it is found to be conservative. Design/methodology/approach This paper has explained a numerical study on the roll-forming process of a channel section and member moment capacities related to the lateral-torsional buckling of the rolled form channel and built-up I-sections beams under uniform bending about its major axis. It has also investigated the effects of residual stresses and strains on the behaviour of this buckling mode. Findings The residuals decrease the moment capacities of the channel beams and have major effect on shorter spans and also increase the local buckling strength of compression flange. But the residuals have major effect on larger spans for built-up I sections. It could be seen that the ratio of moment (with residuals and without residuals) for singly symmetric sections is more pronounced than doubly symmetric sections. So it is recommended to use doubly symmetric section of cold-formed section beams. Originality/value The incorporation of residual stresses and strains in the process of numerical simulation of rolled forming of cold-formed steel sections under end moments is the main contribution of the current work. The effect of residual stresses and strains on the lateral-torsional buckling is, for the first time, addressed in the paper.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-03-14T12:28:59Z
      DOI: 10.1108/IJSI-07-2018-0044
       
  • Dynamic behavior of concrete filled steel tubular columns
    • Pages: 244 - 264
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 244-264, April 2019.
      Purpose The purpose of this paper is to investigate the static and dynamic inelastic response of rigid and semi-rigid connections of steel structures with concrete-filled steel tube (CFST) columns built in high seismic areas, and to compare it with those with open section columns. Design/methodology/approach CFST columns are frequently used in moment resistant steel frames located in seismic areas due to their inherent advantages, including their ductility, energy absorption capacity as well as their high bearing capacity. The smart combination of steel and concrete makes it possible to benefit from the advantages of both components to the maximum. This research work presents the nonlinear dynamic response of moment resistant steel frames with CFST columns, with rigid or semi-rigid connections, built in high seismic areas, according to the Algerian seismic code RPA 99/2003, European EC8 and American FEMA 356 to show the nonlinear characteristics of this type of structures, and their advantages over steel frames with open section columns. Findings The paper presents the advantages of using CFST columns with rigid and semi-rigid connections on the seismic response of portal steel frames. A high performance level in terms of ductility, plastic hinges distribution and their order of appearance has been obtained. It also shows the low effect of seismic loading on the structural elements with CFST columns compared to structures with open section columns. Originality/value The investigation of the numerical results has shown the possibility of their use in the seismic areas for their adequate performance, and also with respect to the design limits specified in the seismic guidelines. In addition, this study represents a first step to develop seismic performance factors for steel structures with CFST columns in Algeria, where the Algerian code do not include a comprehensive specification for the composite steel structures.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-01-30T11:14:48Z
      DOI: 10.1108/IJSI-07-2018-0040
       
  • Damage assessment of reinforced concrete flat slabs through modal tests
           using impact excitation
    • Pages: 265 - 275
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 265-275, April 2019.
      Purpose In reinforced concrete (RC) structures, an evidence of damage is the presence of cracking. In order to evaluate the effect of damage on cracking pattern and natural frequency in RC slabs, two of such structures with different dimensions and reinforcement ratios were tested, in which cracks were induced through application of static load, followed by modal tests using impact excitation. The paper aims to discuss this issue. Design/methodology/approach The gradient of the fundamental natural frequency along the decay, the crack opening rate and also a global damage index based on changes of the fundamental natural frequency were evaluated. Findings The behaviour of the aforementioned gradient was distinct for both slabs, increasing monotonically with the cracking level for the slab with lowest reinforcement ratio, and increasing until 33 per cent of the collapse load and then decreasing afterwards for the slab with the highest ratio. Changes of the gradient were consistent with changes of the crack opening rate. Both results of gradient changes and cracking pattern brought evidence that the balance between open (old) and breathing (new) cracks differed between the slabs, and may be responsible for such differences. Originality/value Damage assessment in RC structures using vibration tests is mostly concentrated on beams. In this work, an advance is made by investigating slabs. The lack of a unique pattern of changes of the gradient implies that its absolute value is not generally suitable for the association with the damage level. However, the impact tests can be effectively used to detect early damage on slabs using this proposed parameter.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-02-07T11:07:21Z
      DOI: 10.1108/IJSI-08-2018-0049
       
  • Sensitivity analysis of beam–column joint rotation angles with respect
           to the stiffnesses of the columns of frame structures
    • Pages: 276 - 288
      Abstract: International Journal of Structural Integrity, Volume 10, Issue 2, Page 276-288, April 2019.
      Purpose Damage detection of frame structures is important for guaranteeing the safety of people’s lives and property. Sensitivity analysis is an effective method for damage identification. The purpose of this paper is to conduct a sensitivity analysis of beam–column joint rotation angles for frame structures with limited flexural stiffness beams. Design/methodology/approach First, based on the D-value method and the assumption of inflection points, statically indeterminate frames were transformed to statically determinate structures, and the expressions of beam–column joint rotation angles were derived. Next, the sensitivity coefficients of beam–column joint rotation angles were obtained by taking the derivative of the expressions of beam–column joint rotation angles with respect to the linear stiffness of column. Finally, the expressions of the sensitivity coefficients were verified by a numerical example. Findings The analytical solutions of the sensitivity coefficients are in good agreement with finite element results. The results show that the beam–column joint rotation angles of damaged column decrease and those of intact columns within the same story increase when damage occurs. Originality/value In this study, the sensitivity coefficients of beam–column joint rotation angles with respect to the linear stiffnesses of columns were derived for frame structures. Based on the result of the sensitivity analysis, the relationship between the changes of beam–column joint rotation angles and damaged columns is revealed. The findings provide an important base to further detect damage of frame structures.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-01-30T11:14:51Z
      DOI: 10.1108/IJSI-07-2018-0041
       
  • Elastic wave mode conversion phenomenon in glass fiber-reinforced polymers
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to present the results of experimental analysis of the elastic-guided wave mode conversion phenomenon in glass fiber-reinforced polymers. The results of this research presented in this paper are strictly focused on S0/A0’ mode conversion phenomenon caused by discontinuities in the form of circular Teflon inserts (artificial delaminations) and impact damage. Results of this research could be useful in problems of damage detection and localization. Design/methodology/approach In the research, guided waves are excited using a piezoelectric transducer and sensed in a non-contact manner using a scanning laser Doppler vibrometer. Full wavefield measurements are analyzed. Analysis of the influence of investigated discontinuities on S0/A0’ mode conversion is based on the elastic wave mode filtration in frequency-wavenumber domain. Mode filtration process allows us to remove the effects of the propagation of unwanted type of mode in forward or backward direction. Effects of S0/A0’ mode conversion are characterized by a mode conversion indicator (MCI) based on the amplitude of new mode A0’ and the amplitude of incident S0 mode. Findings It was noticed that the magnitude of MCI depends on the depth at which the Teflon inserts were located for all analyzed excitation frequencies and diameters of inserts (10 and 20 mm). The magnitude of MCI also increases with increasing impact energies. The S0/A0’ mode conversion phenomenon could be utilized for the detection of surface and internal located discontinuities. Originality/value This paper presents the original results of this research related to the influence of discontinuity location with respect to the sample thickness and severity of discontinuity on S0/A0’ mode conversion.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-28T11:18:12Z
      DOI: 10.1108/IJSI-10-2018-0061
       
  • Rainwater propeller pumps structural integrity
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to focus on the structural integrity of the rainwater propeller pumps installed in the municipal wastewater treatment plant (WTP). Design/methodology/approach A numerical analysis is performed to determine the maximum shear stress on the fasten bolts. The rainwater propeller pump is examined in operation at normal conditions and when one blade is progressively blocked. Findings The failure mechanism of the rainwater pump impeller is determined. Research limitations/implications The fibbers and wastes are discharged together with rainwater during storms with these types of pumps to avoid the flood of the WTP. Several catastrophic events have occurred in service due to the fibbers clog the gap between the impeller blades and the pump casing. The clogging process is partially understood so actual technical solutions deal with effects rather the main causes. Practical implications The operation time of all seven rainwater pumps installed in Timisoara’s WTP is investigated. Climate changes in Banat region and new waste properties found in the wastewater require appropriate technical solutions. A technical solution is proposed based on these investigations to extend the operation time and to diminish the operation and maintenance costs. Social implications These large pumps are installed in the urban sewage centralised system implemented in the most cities. The access to the sewerage network is a requirement of any community, regardless of the social status. Originality/value The fracture surfaces of both fastening bolts of the rainwater pump impellers produced in service are examined. As a result, it has been identified that the catastrophic events are due to the brittle fracture of both fasten bolts between the impeller blades and the pump hub, respectively. The catastrophic events of the rainwater propeller pumps are directly correlated to the clog level of the impeller. The numerical simulation is performed to determine the maximum shear stress on the fasten bolts. The case with pump operating at normal conditions is performed identifying its vulnerabilities to clog conditions. Next, one impeller blade is progressively blocked considering three time stop scenarios associated with different clog levels. Conclusively, the operating time of the rainwater pump up to the catastrophic failure is correlated to the clog level of the impeller.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-27T09:49:46Z
      DOI: 10.1108/IJSI-10-2018-0070
       
  • Finite element method for solving asphalt mixture problem
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Asphalt mixture is widely used in road engineering, and its performance research is particularly important. But the study of asphalt mixture performance needs a lot of tests, such as bending test, splitting test and so on. It also needs a lot of time and material resources. The purpose of this paper is to obtain test results through finite element numerical simulation, and show that this saves a lot of manpower and material resources. Design/methodology/approach The mechanical parameters of the material are obtained through uniaxial compression tests. The true stress and plastic strain are calculated according to nominal stress and nominal strain. A constitutive model is established. Then a finite element model of asphalt mixture is established. The numerical simulation and performance study of asphalt mixture bending test is carried out. At the same time, according to the above method, the asphalt mixture is subjected to freeze-thaw cycles and ultraviolet aging, and the mechanical parameters are obtained by a uniaxial compression test. A numerical model is established to simulate the bending characteristics of asphalt mixture after freeze-thaw cycles and ultraviolet aging. Findings A uniaxial compression test of the asphalt mixture is conducted to obtain nominal stress and nominal strain. The true stress and plastic strain are calculated and the elastic modulus is established with Poisson’s ratio as the elastic part, and the true stress and plastic strain as the plastic part. The model is constructed, the finite element model is established and the bending test is numerically simulated. The verified trend is consistent, and the method is feasible. According to the above method, the concrete is subjected to freeze-thaw cycle and ultraviolet aging, and the finite element model is established by using uniaxial compression test to obtain parameters. The bending test is simulated and the verification method is feasible. With the increase of the number of freeze-thaw cycles and the increase of UV aging time, the maximum bending strain of SBS modified asphalt mixture and matrix asphalt mixture is decreased .The low-temperature performance of SBS modified asphalt mixture is better than that of matrix asphalt mixture. Originality/value A method of simulating asphalt mixture test by finite element method numerical simulation is established. By using this method, the performance of asphalt mixture is studied, which saves a lot of manpower and material resources. At the same time, this method can be used to study the characteristics of asphalt mixture under complex conditions.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-26T07:18:02Z
      DOI: 10.1108/IJSI-09-2018-0052
       
  • Experimental investigation of zeolite and limestone powder on
           self-compacting concrete strength after early loading
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Modern construction methods have been developed with the goal of reducing construction time as much as possible, which results in some situations during construction and within the first few days after it, when concrete is subjected to exceptionally high loads. The precast concrete, which is the concrete in very early ages, may result in severe cracks or damages. In conventional construction projects, sometimes working with concrete, which had not reached its ultimate strength, is an unavoidable matter of fact. This paper aims to discuss these issues. Design/methodology/approach Researchers in the field of construction materials have done their best to make some changes in the different parts of the concrete in order to bring about reforms, based on the existing needs, and achieve new quality and primacy from concrete. One kind of concrete, the emergence of which dates back to many years ago, is self-compacting concrete. Thanks to its high efficiency for the parts with complex forms of high-density steel, this kind of concrete suggests new prospects. Findings This study aims at evaluating the effect of early loads on the 28-day compressive strength of concretes with zeolite and limestone powder under different curing conditions (wet or dry). In this regard, two self-compacting concrete mix designs with the same ratio of water to cementations materials and 0.4 percent and 10 percent zeolite have been considered; therefore, concrete cube samples with zeolite and limestone powder in different curing conditions at ages of three, one and seven days under preloading with 80–90 percent of compressive strength are damaged, and after curing in different conditions, their 28-day compressive strength is measured. According to the results, the recovery of the 28-day compressive strength of damaged samples, compared to that of intact samples, is possible in all curing conditions. The experiments that have been performed on concrete samples under dry and wet curing conditions show that the full recovery of compressive strength of damaged samples compared to that of intact ones happened only in preloaded samples at the age of one days, and in other ages (three and seven days) the 28-day strength reduction has occurred in damaged samples compared to the that in intact samples. The results of concrete samples with zeolite and without limestone powder at the age of one day indicate the greatest impact on other samples on the 28-day compressive strength of damaged samples compared to that of intact ones, occurring under dry condition. Originality/value This research analyzed and studied the influence under wet and dry curing conditions and the presence of limestone powder and zeolite fillers in recovering of the 28-day compressive strength of preloaded concrete samples at early stages (one, three and seven days) after the construction of the concrete.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-20T08:02:32Z
      DOI: 10.1108/IJSI-05-2018-0031
       
  • Simulation of the thermomechanical behavior of graphene/PMMA
           nanocomposites via continuum mechanics
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to simulate and investigate the thermomechanical properties of graphene-reinforced nanocomposites. Design/methodology/approach The analysis proposed consists of two stages. In the first stage, the temperature-dependent mechanical properties of graphene are estimated while in the second stage, using the previously derived properties, the temperature-dependent properties of graphene-reinforced PMMA nanocomposites are investigated. In the first stage of the analysis, graphene is modeled discretely using molecular mechanics theory where the interatomic interactions are simulated by spring elements of temperature-dependent stiffness. The graphene sheets are composed of either one or more (up to five) monolayer graphene sheets connected via van der Waals interactions. However, in the second analysis stage, graphene is modeled equivalently as continuum medium and is positioned between two layers of PMMA. Also, the interphase between two materials is modeled as a medium with mechanical properties defined and bounded by the two materials. Findings The mechanical properties including Young’s modulus, shear modulus and Poisson’s ratio due to temperature changes are estimated. The numerical results show that the temperature rise and the multiplicity of graphene layers considered lead to a decrease of the mechanical properties. Originality/value The present analysis proposes an easy and accurate method for the estimation of the temperature-dependent mechanical properties of graphene-reinforced nanocomposites.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-20T08:00:31Z
      DOI: 10.1108/IJSI-10-2018-0078
       
  • Towards hybridization of composite patch in repair of cracked Aluminum
           panel
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The maintenance of aircraft structure with lower cost is one of the prime concerns to regulatory authorities. The carbon fiber-reinforced polymer (CFRP) patches are widely used to repair the cracked structure. The demands and application of CFRP compel its price to increase in the near future. A distinct perspective of repairing the cracked aluminum panel with the hybrid composite patch is presented in this paper. The purpose of this paper is to propose an alternative patch material in the form of a hybrid composite patch which can provide economical repair solution. Design/methodology/approach The patch hybridization is performed by preparing the hybrid composite from tows of carbon fiber and glass fiber. Rule of hybrid mixture and modified Halpin–Tsai’s equation are used to evaluate the elastic constant. The stress intensity factor and interfacial stresses are determined using finite element analysis. The debonding initiation load is evaluated after testing under mode-I loading condition. Findings The hybrid composite patch has rendered the adequate performance for reduction of stress intensity in the cracked panel and control of interfacial stresses in the adhesive layer. The repair efficiency and repair durability of the composite patch repair was ensured by incorporation of the hybrid composite patch. Originality/value The studies involving patch hybridization for the application of composite patch repair are presently lacking. The influence of the patch stiffness, methodology to prepare the hybrid composite patch and effects of hybridization on the performance of composite patch repair is presented in this paper.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-20T01:57:22Z
      DOI: 10.1108/IJSI-03-2019-0015
       
  • Combining FEM and MD to simulate C60/PA-12 nanocomposites
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is the computation of the elastic mechanical behaviour of the fullerene C60 reinforced polyamide-12 (PA-12) via a two-stage numerical technique which combines the molecular dynamics (MD) method and the finite element method (FEM). Design/methodology/approach At the first stage, the proposed numerical scheme utilizes MD to characterize the pure PA-12 as well as a very small cubic unit cell containing a C60 molecule, centrally positioned and surrounded by PA-12 molecular chains. At the second stage, a classical continuum mechanics (CM) analysis based on the FEM is adopted to approximate the elastic mechanical performance of the nanocomposite with significantly lower C60 mass concentrations. According to the computed elastic properties arisen by the MD simulations, an equivalent solid element with the same size as the unit cell is developed. Then, a CM micromechanical representative volume element (RVE) of the C60 reinforced PA-12 is modelled via FEM. The matrix phase of the RVE is discretized by using solid finite elements which represent the PA-12 mechanical behaviour predicted by MD, while the C60 neighbouring location is meshed with the equivalent solid element. Findings Several multiscale simulations are performed to study the effect of the nanofiller mass fraction on the mechanical properties of the C60 reinforced PA-12 composite. Comparisons with other corresponding experimental results are attempted, where possible, to test the performance of the proposed method. Originality/value The proposed numerical scheme allows accurate representation of atomistic interfacial effects between C60 and PA-12 and simultaneously offers a significantly lower computational cost compared with the MD-only method.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-12T01:22:55Z
      DOI: 10.1108/IJSI-10-2018-0071
       
  • Computer simulation of weld toe stress concentration factor sequence for
           fatigue analysis
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to complete fatigue analysis of welded joints considering both the crack initiation sites and crack coalescence, and to generate virtual welded specimens for computer simulation of fatigue life on a specimen-by-specimen basis; knowledge regarding the weld toe stress concentration factor (SCF) sequence is essential. In this study, attempts were made to analyze the sequence and to find a simple method to generate the sequence using computers. Design/methodology/approach Laser scanning technique was used to acquire the real three-dimensional weld toe geometry of welded specimens. The scanned geometry was digitally sectioned, and three-dimensional finite element (FE) models of the scanned specimens were constructed and the weld toe SCF sequence was calculated. The numbers in the sequence were analyzed using a simple autoregression model and the statistical properties of the sequence were acquired. Findings The autoregression analysis showed the value of a weld toe SCF is linearly related to its neighboring factor with a high correlation. When a factor value at a toe location is known, the neighboring factor can be simulated by a simple linear equation with a random residual. The weld toe factor sequence can thus be formed by repeatedly using the linear equation with a residual. The generated sequence exhibits close statistical properties to those of the real sequence obtained from FE results. Practical implications When the weld toe SCF sequence is known, it is possible to foresee potential crack locations and the subsequent crack coalescence. The results of the current study will be the foundation for the future work on fatigue analysis of welded joints considering the effects of crack initiation site and crack coalescence. Originality/value The weld toe SCF sequence was rarely discussed previously because of a lack of the available data. The current study is the first work to investigate the statistical properties of the sequence and found that a simple autoregression equation can be used to perform the analysis. This study is also the first work that successfully generates a weld toe SCF sequence, which can be used to simulate virtual welded specimens.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-10T03:53:54Z
      DOI: 10.1108/IJSI-11-2018-0086
       
  • Capability of non-destructive techniques in evaluating damage to composite
           sandwich structures
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Defects can be caused by a number of factors, such as maintenance damage, ground handling and foreign objects thrown up from runways during an in-service use of composite aerospace structures. Sandwich structures are capable of absorbing large amounts of energy under impact loads, resulting in high structural crashworthiness. This situation is one of the many reasons why sandwich structures are extensively used in many aerospace applications nowadays. Their non-destructive inspection is often more complex. Hence, the choice of a suitable non-destructive testing (NDT) method can play a key role in successful damage detection. The paper aims to discuss these issues. Design/methodology/approach A comparison of detection capabilities of selected C-scan NDT methods applicable for inspections of sandwich structures was performed using water-squirt, air-coupled and pitch-catch (PC) ultrasonic techniques, supplemented by laser shearography (LS). Findings Test results showed that the water-squirt and PC techniques are the most suitable methods for core damage evaluation. Meanwhile, the air-coupled method showed lower sensitivity for the detection of several artificial defects and impact damage in honeycomb sandwiches when unfocussed transducers were used. LS can detect most of the defects in the panels, but it has lower sensitivity and resolution for honeycomb core-type sandwiches. Originality/value This study quantitatively compared the damage size indication capabilities of sandwich structures by using various NDT techniques. Results of the realised tests can be used for successful selection of a suitable NDT method. Combinations of the presented methods revealed most defects.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-07T01:22:23Z
      DOI: 10.1108/IJSI-10-2018-0067
       
  • Investigations on prying forces in flexible connections of steel beams
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The use of flexible connections throughout the steel structures provides a high level of stiffness compared to that of fully welded connections. Flexible connections allow for rotation to an extent, which make them perform better during earthquake than welded connections. In hanger connections, the applied load produces tension in the bolts and bolts are designed for tensile forces. When the deformation of the flange plate is equal to that of the bolts, a plastic hinge is formed in the flange plate at the weld line and the bolts are pulled to failure. If the attached plate is allowed to deform, additional tensile forces called prying forces are developed in the bolts. The paper aims to discuss these issues. Design/methodology/approach This paper includes the results of investigation on prying force in T-stub connection fabricated with normal grade bolts and high strength friction grip (HSFG) bolts. Finite element analysis has been carried out by creating models and analyzing the effect of external tensile force and bolt force. For different grades of bolt (4.6, 8.8, 10.9, 12.9), the prying force is calculated. Findings It is found that prying force is increasing with the change in grade of bolt used from normal to HSFG. The results obtained from analysis using IS 800:2007 codal provision are also included. It is observed that HSFG bolts do not allow for any slip between the elements connected and hence rigidity is increased. Originality/value The prying force mainly depends on geometrical parameter of the connection. In this research work, the variation of prying force was studied based on the variation in dimensions of T-stub angle section and bolt grade (4.6, 8.8, 10.9, 12.9). The method of obtaining prying force from bolt load and applied load is a unique approach. The results of FE analysis is validated with the analytical calculation as per IS 800:2007 code provisions, which shows the originality of the research.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-07T01:19:03Z
      DOI: 10.1108/IJSI-01-2019-0003
       
  • Optimization of process parameters of wire electro discharge machining for
           Ti49.4Ni50.6 shape memory alloys using the Taguchi technique
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Ti49.4Ni50.6 (at. %) shape memory alloy (SMA) is a unique class of smart materials because of unbeatable property which given a wide variety of their applications across a broad range of fields including an orthopedic implant. It plays a very important role in the constructions of novel orthopedic implants application (like dynamic compression plate) because of lower Young’s modulus compared to other biomedical implant materials, high mechanical strength, excellent corrosion resistance and unique property like shape memory effect. Conventional machining of Ti-Ni yields poor surface finish and low dimensional accuracy of the machined components. Hence, wire electro-discharge machining (WDEM) of Ti-Ni has been performed. The purpose of this paper is to investigate the effect of variation of five process parameters, namely, a pulse-on time, pulse-off time, spark gap set voltage (SV), wire feed and wire tension on the material removal rate, surface roughness (SR), kerf width (KW) and dimensional deviation (DD), in the WDEM of Ti49.5Ni50.6 SMA. Design/methodology/approach The effect of machining parameters on Ti49.4Ni50.6 has been fully explored using WEDM with zinc coated brass wire as an electrode. In this work, L18 orthogonal array based on Taguchi method has been used to conduct a series of experiments and statically evaluate the experimental data by the use of the method of analysis of variance. Scanning electron microscope images of the machined surface, at the highest and lowest pulse-on time, have been taken to evaluate the quality of surface in terms of their SR values. Findings For the highest pulse-on time, it is observed that blow holes, cracks, melted droplets and craters have been formed on the machined surface with an SR of 2.744 µm, while for the lowest pulse-on time, these are not formed with an SR of 0.862 µm. It is seen that the pulse-on time is the most significant process parameter for MRR, SR and KW, while the DD is significantly affected by spark gap SV. The optimal values of the process parameters have been obtained by the method of analysis of mean and the confirmatory experiments have been carried out to validate results of optimization. Energy dispersive spectroscopy analysis of the machined surface of Ti49.4Ni50.6 has shown a certain amount of deposition of material on the machined surface. Originality/value This is an original paper.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-07T01:15:23Z
      DOI: 10.1108/IJSI-10-2018-0058
       
  • A study on prognostic analysis of attachment lugs under off-axis loading
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Lug joints with fasteners play a crucial role in connecting many major components of the aircraft. Most of the failures in the past were credited to the damages initiating and progressing from these types of joints. Ensuring the structural integrity of these fastener joints is a major issue in many engineering structures, especially in aerospace components, which would otherwise lead to fatal failure. The purpose of this paper is to adopting the prognostic approach for analysing these lug joints with fasteners subjected to off-axis loading by estimating the crack initiation and crack growth life of these joints. This data will be useful to estimate the remaining life of these joints at any given stage of operations, which is mandatory in structural health monitoring (SHM). Design/methodology/approach Straight and tapered lug joints are modelled using the finite element method in MSC PATRAN and analysed in MSC NASTRAN. These lug joints are analysed with a push fit fastener. The contact/separation regions at the pin–lug interface are carefully monitored throughout the analysis for various loading conditions. Critical locations in these lug joints are identified through stress analysis. Fatigue crack initiation and fatigue crack growth analysed is carried out at these locations for different load ratios. A computational method is proposed to estimate the cycles to reach crack initiation and cycles at which the crack in the lug joint become critical by integrating several known techniques. Findings Analysis carried out in this paper describes the importance of tapered lug joints, particularly when subjected to non-conventional way of loading, i.e. off-axis loading. There is a partial loss of contact between pin and lug upon pin loading, and this does not change further with monotonically increasing pin load. But during load reversals, there is a change in contact/separation regions which is effectively handled by inequality constraints in the boundary conditions. Crack growth in these lug joints pertains to mixed-mode cracking and is computed through the MVCCI technique. Originality/value Most of the earlier works were carried out on in-plane pin loading along the axis of symmetry of the lug. The current work considers the off-axis pin loading by loading the lug joints with transverse and oblique pin load. The significance of taper angle under such loading condition is brought in this paper. The results obtained in this paper through prognostic approach are of direct relevance to the SHM and damage tolerance design approach where the safety of the structural components is of foremost priority.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-06-04T11:06:02Z
      DOI: 10.1108/IJSI-10-2018-0075
       
  • Dynamic analysis of swivel construction method under multi-variable
           coupling effects
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Swivel construction is a new bridge construction method, which can minimize the impact on railway and highway traffic. Previous studies were based on single factor and static analysis, which cannot reflect the real state of structures. The purpose of this paper is to establish a dynamic model of the structure and to analyze the situation under multi-variable coupling effects to accurately simulate the real state of the structure. Design/methodology/approach Finite element software ANSYS was used to establish dynamic model of turntable structure and then to analyze the effects of multiple factors on total stress, friction stress and slipping distance of the turntable structure. Findings It is concluded that the unbalanced weight and radius of spherical hinges have great influence on the turntable structure, so the design should be strictly considered. Friction stress and angular acceleration have little effect on the turntable structure. Originality/value This paper provides simulation of the whole process of swivel construction method. Whereas previous studies focused on static analysis, this paper focuses on the dynamic analysis of swivel construction method. The mechanics of the swivel structure under multiple factors was analyzed. According to the analysis results, the design parameters of the turntable structure are optimized.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-05-31T01:44:15Z
      DOI: 10.1108/IJSI-10-2018-0074
       
  • Failure investigation of Cu-DHP tubes due to ant-nest corrosion
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to address the main aspects of ant-nest corrosion failure mechanism of a Cu tube in heating ventilation and air-conditioning (HVAC) installations and analyze the possible root causes through various case studies presented. Design/methodology/approach Failure investigation process includes mainly stereo-, light optical and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy for elemental microanalysis, as the main analytical techniques for material characterization and root-cause analysis. Findings The investigation findings, obtained from corrosion products’ analysis in conjunction to metallographic evaluation in transverse sections, illustrate the principal characteristics (“fingerprints”) of ant-nest (formicary) corrosion mechanism. Originality/value This paper which deals with the presentation of applied failure analysis/case histories’ investigation, summarizing the main aspects of an important and insidious type of Cu corrosion, taken place in HVAC installation systems and, on the other hand, presenting a complementary analysis of the chemical processes involved in the progressive failure mechanism constitutes an integrated approach, aiming to become a concise contribution to this subject.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-05-31T01:24:50Z
      DOI: 10.1108/IJSI-09-2018-0056
       
  • Ballistic impact of steel fiber-metal laminates and plates
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to investigate the ballistic impact response of square clamped fiber-metal laminates and monolithic plates consisting of different metal alloys using the ANSYS LS-DYNA explicit nonlinear analysis software. The panels are subjected to central normal high velocity ballistic impact by a cylindrical projectile. Design/methodology/approach Using validated finite element models, the influence of the constituent metal alloy on the ballistic resistance of the fiber-metal laminates and the monolithic plates is studied. Six steel alloys are examined, namely, 304 stainless steel, 1010, 1080, 4340, A36 steel and DP 590 dual phase steel. A comparison with the response of GLAss REinforced plates is also implemented. Findings It is found that the ballistic limits of the panels can be substantially affected by the constituent alloy. The stainless steel based panels offer the highest ballistic resistance followed by the A36 steel based panels which in turn have higher ballistic resistance than the 2024-T3 aluminum based panels. The A36 steel based panels have higher ballistic limit than the 1010 steel based panels which in turn have higher ballistic limit than the 1080 steel based panels. The behavior of characteristic impact variables such as the impact load, the absorbed impact energy and the projectile’s displacement during the ballistic impact phenomenon is analyzed. Originality/value The ballistic resistance of the aforementioned steel fiber-metal laminates has not been studied previously. This study contributes to the scientific knowledge concerning the impact response of steel-based fiber-metal laminates and to the construction of impact resistant structures.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-05-31T01:19:31Z
      DOI: 10.1108/IJSI-10-2018-0060
       
  • Piston-ring performance: limitations from cavitation and friction
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Cavitation in piston-ring lubrication is studied as part of the performance of piston-ring assemblies. Cavitation degrades performance in engineering applications and its effect is that it alters the oil film pressure, generated at the converging-diverging wedge of the interface. Studies tried to shed light to the phenomenon of cavitation and compare it with cavities that have been identified in bearings. The paper aims to discuss this issue. Design/methodology/approach Lubricant formulations were used for parametric study of oil film thickness (OFT) and friction providing the OFT throughout the stroke and LIF for OFT point measurements. Lubricant formulation affects cavitation appearance and behaviour when fully developed. Findings Cavitation affects the ring load carrying capacity. Different forms of cavitation were identified and their shape and size (length and width) is dictated from reciprocating speed and viscosity of the lubricant. A clear picture is given from both techniques and friction results give quantifiable data in terms of the effect in wear and cavitation, depending on the lubricant properties. Research limitations/implications Engine results are limited due to manufacturing difficulties of visualisation windows and oil starvation. Therefore, full stroke length sized windows were not an option and motoring tests were implemented due to materials limitations (adhesive and quartz windows). Lubricant manufacturer has to give data regarding the chemistry of the lubricants. Originality/value The contribution of cavitation in piston-ring lubrication OFT, friction measurements and lubricant parameters that try to shed light to the different forms of cavitation. A link between viscosity, cavitation, shear thinning properties, OFT and friction is given.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-05-31T01:15:12Z
      DOI: 10.1108/IJSI-09-2018-0053
       
  • A numerical approach to determine fiber orientations around geometric
           discontinuities in designing against failure of GFRP laminates
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose Determining fiber orientations around geometric discontinuities is challenging and simultaneously crucial when designing laminates against failure. The purpose of this paper is to present an approach for selecting the fiber orientations in the vicinity of a geometric discontinuity; more specifically round holes with edge cracks. Maximum stresses in the discontinuity region are calculated using Classical Lamination Theory (CLT) and the stress concentration factor for the aforementioned condition. The minimum moment to cause failure in a lamina is estimated using the Tsai–Hill and Tsai–Wu failure theories for a symmetric general stacking laminate. Fiber orientations around the discontinuity are obtained using the Tsai–Hill failure theory. Design/methodology/approach The current research focuses on a general stacking sequence laminate under three-point bending conditions. The laminate material is S2 fiber glass/epoxy. The concepts of mode I stress intensity factor and plastic zone radius are applied to decide the radius of the plastic zone, and stress concentration factor that multiplies the CLT stress distribution in the vicinity of the discontinuity. The magnitude of the minimum moment to cause failure in each ply is then estimated using the Tsai–Hill and Tsai–Wu failure theories, under the aforementioned stress concentration. Findings The findings of the study are as follows: it confirms the conclusions of previous research that the size and shape of the discontinuity have a significant effect on determining such orientations; the dimensions of the laminate and laminae not only affect the CLT results, but also the effect of the discontinuity in these results; and each lamina depending on its position in the laminate will have a different minimum load to cause failure and consequently, a different fiber orientation around the geometric discontinuity. Originality/value This paper discusses an important topic for the manufacturing and design against failure of Glass Fiber Reinforced Plastic (GFRP) laminated structures. The topic of introducing geometric discontinuities in unidirectional GFRP laminates is still a challenging one. This paper addresses these issues under 3pt bending conditions, a load condition rarely approached in literature. Therefore, it presents a fairly simple approach to strengthen geometric discontinuity regions without discontinuing fibers.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-05-13T02:14:24Z
      DOI: 10.1108/IJSI-10-2018-0064
       
  • Shear strength and temperature distribution model of friction spot lap
           joint of high density polyethylene with aluminum alloy 7075
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to join a sheet of the AA7075 with the high-density polyethylene (HDPE) by a lap joint using friction spot processing and investigate the temperature distribution of joint during this process using the finite element method (FEM). Design/methodology/approach A semi-conical hole was manufactured in the AA7075 specimen and a lap joint configuration was prepared with the HDPE specimen. A rotating tool was used to generate the required heat to melt the polymer by the friction with the AA7075 specimen. The applied tool force moved the molten polymer through the hole. Four parameters were used: lower diameter of hole, rotating speed, plunging depth and time. The results of shear test were analyzed using the Taguchi method. A FEM was presented to estimate the temperature distribution of joint during the process. Findings All specimens failed by shearing the polymer at the lap joint region without dislocation. The specimens of the smallest diameter exhibited the highest shear strength at the lap joint. The maximum ranges of temperature were recorded at the contact region between the rotating tool and the AA7075 specimen. The tool plunging depth recorded the highest effect on the generated heat compared with the rotating speed and plunging time. Originality/value For the first time, the AA7075 sheet was joined with the HDPE sheet by friction spot processing. The temperature distribution of this joint was simulated using the FEM.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-04-18T03:07:22Z
      DOI: 10.1108/IJSI-05-2018-0025
       
  • Dynamic analysis of a cracked bar by the method of characteristics
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to introduce a new numerical approach for studying a cantilever bar having a transverse crack. The crack is modeled by an elastic longitudinal spring with a stiffness K according to Castiglione’s theorem. Design/methodology/approach The bar is excited by different longitudinal impulse forces. The considered problem based on the differential equation of motion is solved by the method of characteristics (MOC) after splitting the second-order motion equation into two first-order equivalent equations. Findings In this study, effects of the crack size and crack’s position on the reflected waves from the crack are investigated. The results indicate that the presence of the crack in the cantilever bar generates additional waves caused by the reflection of the incident wave by the crack. Originality/value A numerical approach developed in this paper is used for detecting the extent of the damage in cracked bars by the measurement of the difference between the dynamic response of an uncracked bar and a cracked bar.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-04-11T03:23:44Z
      DOI: 10.1108/IJSI-01-2018-0001
       
  • Structural-probabilistic modeling of fatigue failure under elastic-plastic
           deformation
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to consider an approximate model of accumulation of microdefects in a material under repeated loading which makes it possible to define theoretical parameters of the fatigue failure (durability, fatigue limit, etc.). The model is involving the relevant law of distribution of ultimate (yield) stresses in the material of these members in combination with the basic characteristics of main mechanical properties of a material (ultimate and yield stresses and associated standard deviations). Design/methodology/approach The model of fatigue failure of brittle and elastoplastic materials based on the use of the structural-probabilistic approach and up-to-date ideas on the mechanism of material fracture is proposed. The model combines statistical fracture criteria, which are expressed in terms of damage concentrations, with the approximate model of microcrack accumulation under repeating loading of the same level. According to these criteria, the fatigue failure begins with the accumulation of separation- or shear-type microdefects up to the level of critical values of their density. Findings The failure mechanism is associated with the accumulation of dispersed microdamages under repeated loading. The critical value of the density of the microdamages, which are identified with those formed either by separation or shear under static loading in consequence of simple tension, compression or shear, is accepted as the criterion of the onset of fatigue failure. The fatigue being low-cycle or high-cycle is attributed to accumulation of shear microdamages in the region of plastic deformation in the former case and microdamages produced by separation under elastic deformation in the latter one. Originality/value The originality of the paper consists in the following. The authors theoretically define parameters of the fatigue failure (durability, fatigue limit, etc.) using the model in combination with the statistical failure (yield) criteria appearing in the damage measures. The constructed fatigue diagram has discontinuities on the conditional boundary dividing domains with the shear-type and separation-type fractures of structural elements. Such results are supported by the experimental results.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-03-14T12:29:29Z
      DOI: 10.1108/IJSI-05-2018-0024
       
  • Numerical simulation of fatigue crack propagation in mixed-mode (I+II)
           using the program BemCracker2D
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to present the application of the boundary element method (BEM) in linear elastic fracture mechanics for analysis of fatigue crack propagation problems in mixed-mode (I+II) using a robust academic software named BemCracker2D and its graphical interface BemLab2D. Design/methodology/approach The methodology consists in calculating elastic stress by conventional BEM and to carry out an incremental analysis of the crack extension employing the dual BEM (DBEM). For each increment of the analysis, the stress intensity factors (SIFs) are computed by the J-Integral technique, the crack growth direction is evaluated by the maximum circumferential stress criterion and the crack growth rate is computed by a modified Paris equation, which takes into account an equivalent SIF to obtain the fracture Modes I and II. The numerical results are compared with the experimental and/or BEM values extracted from the open literature, aiming to demonstrate the accuracy and efficiency of the adopted methodology, as well as to validate the robustness of the programs. Findings The paper addresses the numerical simulation of fatigue crack growth. The main contribution of the paper is the introduction of a software for simulating two-dimensional fatigue crack growth problems in mixed-mode (I+II) via the DBEM. The software BemCracker2D coupled to the BemLab2D graphical user interface (GUI), for pre/post-processing, are very complete, efficient and versatile and its does make relevant contributions in the field of fracture mechanics. Originality/value The main contribution of the manuscript is the development of a GUI for pre/post-processing of 2D fracture mechanics problems, as well as the object oriented programming implementation. Finally, the main merit is of educational nature.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-03-14T11:59:48Z
      DOI: 10.1108/IJSI-04-2018-0022
       
  • Durability analysis using Markov chain modeling under random loading for
           automobile crankshaft
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to present the durability analysis in predicting the reliability life cycle for an automobile crankshaft under random stress load using the stochastic process. Due to the limitations associated with the actual loading history obtained from the experimental analysis or due to the sensitivity of the strain gauge, the fatigue reliability life cycle assessment has lower accuracy and efficiency for fatigue life prediction. Design/methodology/approach The proposed Markov process embeds the actual maximum and minimum stresses by a continuous updating process for stress load history data. This is to reduce the large credible intervals and missing loading points used for fatigue life prediction. With the reduction and missing loading intervals, the accuracy of fatigue life prediction for the crankshaft was validated using the statistical correlation properties. Findings It was observed that fatigue reliability corresponded well by reporting the accuracy of 95–98 per cent with a mean squared error of 1.5–3 per cent for durability and mean cycle to failure. Hence, the proposed fatigue reliability assessment provides an accurate, efficient, fast and cost-effective durability analysis in contrast to costly and lengthy experimental techniques. Research limitations/implications An important implication of this study is durability-based life cycle assessment by developing the reliability and hazard rate index under random stress loading using the stochastic technique in modeling for improving the sensitivity of the strain gauge. Practical implications The durability analysis is one of the fundamental attributes for the safe operation of any component, especially in the automotive industry. Focusing on safety, structural health monitoring aims at the quantification of the probability of failure under mixed mode loading. In practice, diverse types of protective barriers are placed as safeguards from the hazard posed by the system operation. Social implications Durability analysis has the ability to deal with the longevity and dependability of parts, products and systems in any industry. More poignantly, it is about controlling risk whereby engineering incorporates a wide variety of analytical techniques designed to help engineers understand the failure modes and patterns of these parts, products and systems. This would enable the automotive industry to improve design and increase the life cycle with the durability assessment field focussing on product reliability and sustainability assurance. Originality/value The accuracy of the simulated fatigue life was statistically correlated with a 95 per cent boundary condition towards the actual fatigue through the validation process using finite element analysis. Furthermore, the embedded Markov process has high accuracy in generating synthetic load history for the fatigue life cycle assessment. More importantly, the fatigue reliability life cycle assessment can be performed with high accuracy and efficiency in assessing the integrity of the component regarding structural integrity.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-02-11T12:36:53Z
      DOI: 10.1108/IJSI-03-2018-0016
       
  • Carbon footprint and financial evaluation of an aeronautic component
           production using different manufacturing processes
    • Abstract: International Journal of Structural Integrity, Ahead of Print.
      Purpose The purpose of this paper is to quantify the environmental footprint and cost and thus compare different manufacturing scenarios associated with the production of aeronautical structural components. Design/methodology/approach A representative helicopter canopy, i.e., canopy of the EUROCOPTER EC Twin Star helicopter described in Pantelakis et al. (2009), has been considered for the carbon footprint (life cycle energy and climate change impact analysis) along with the life cycle costing analysis. Four scenarios – combinations of different manufacturing technologies (autoclave and resin transfer molding (RTM)) and end-of-life treatment scenarios (mechanical recycling and pyrolysis) are considered. Findings Using the models developed the expected environmental and cost benefits by involving the RTM technique have been quantified. The environmental impact was expressed in terms of energy consumption and of Global Warming Potential-100. From an environmental standpoint, processing the canopy using the RTM technique leads to decreased energy demands as compared to autoclaving because of the shorter curing cycles exhibited from this technique and thus the less time needed. As far as the financial viability of both processing scenarios is concerned, the more steps needed for preparing the mold and the need for auxiliary materials increase the material and the labor cost of autoclaving as compared to RTM. Originality/value At the early design stages in aeronautics, a number of disciplines (environmental, financial and mechanical) should be taken into account in order to evaluate alternative scenarios (material, manufacturing, recycling, etc.). In this paper a methodology is developed toward this direction, quantifying the environmental and financial viability of different manufacturing scenarios associated with the production of aeronautical structures.
      Citation: International Journal of Structural Integrity
      PubDate: 2019-01-25T01:39:48Z
      DOI: 10.1108/IJSI-07-2018-0043
       
 
 
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