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Authors:Shibing Huang, Chen Cai, Shilin Yu, Yingbo He, Xianze Cui Abstract: International Journal of Damage Mechanics, Ahead of Print. Freeze-thaw action of rocks has caused many engineering geological disasters in cold regions. Estimation of the freeze-thaw damage degree and strengths loss of rocks are crucial for the prevention of freeze-thaw disasters. The main aim of this research is to investigate the influence of water saturation on the deterioration of rocks under freeze-thaw and find the best evaluation index. P-wave velocity, elastic modulus and porosity, as the widely used indexes, were adopted to define the freeze-thaw damage variables and predict the UCS loss under freeze-thaw. The change law of these three indexes shows that the critical water saturation for causing a considerable freeze-thaw damage of sandstones is approximately 60%∼80%. P-wave velocity is proved to be a competitive nondestructive parameter, which can be measured easily and correctly without any time-consuming mechanical test. In addition, P-wave velocity can be well used to predict strength loss of rocks under freeze-thaw by performing a statistical analysis of experimental data. It is suggested that the P-wave velocity may be the primary and best index to quantify the freeze-thaw damage degree of rocks with different water saturations comparison with the other two indexes. This study can provide a better understanding of the deterioration of physico-mechanical properties for unsaturated rocks and give a reference for the selection of freeze-thaw evaluation indexes. Citation: International Journal of Damage Mechanics PubDate: 2022-06-15T05:23:57Z DOI: 10.1177/10567895221106241
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Authors:Liwei Wu, Dan Huang, Qipeng Ma, Zhiyuan Li, Xuehao Yao Abstract: International Journal of Damage Mechanics, Ahead of Print. In this paper, a modified intermediately homogenized peridynamic (IH-PD) model for analyzing impact failure of wet concrete has been presented under the configuration of ordinary state-based peridynamic theory. The meso-structural properties of concrete are linked to the macroscopic mechanical behavior in the IH-PD model, where the heterogeneity of concrete is taken into account, and the calculation cost does not increase. Simultaneously, the porosity of concrete is considered, which is implemented by deleting the bond between two material points, as well as the influence of porosity on the mechanical properties of concrete. Moreover, the effective bulk and shear modulus of cement mortar in wet concrete (saturated and unsaturated concrete) are calculated respectively. The dynamic model for wet concrete is described from three aspects: strength, dynamic increase factor, and equation of state. Validation of the proposed model is established through analyzing some benchmark tests and comparing with the corresponding experiment and other available numerical results. Citation: International Journal of Damage Mechanics PubDate: 2022-06-11T06:14:00Z DOI: 10.1177/10567895221105654
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Authors:Wei-Feng Bai, Wei-Li Wang, Jun-Feng Guan, Jian-you Wang, Chen-yang Yuan Abstract: International Journal of Damage Mechanics, Ahead of Print. Damage evolution in concrete after high temperature is a complicated procedure, in which the pre-peak strain hardening behaviour, the post-peak strain softening behaviour and the impact of high temperature play key roles. Uniaxial and biaxial compression damage models of concrete considering high temperature degradation effect are proposed based on damage theory and experimental phenomena. They consider that the destruction of concrete is actually the cumulative evolution course of the two meso-damage modes, rupture and yield. High temperature changes the mechanical performance in microstructure of concrete and the generation and propagation of microcracks. It could be described by adjusting the probability distributions which characterize the mesoscopic damage evolution. The damage constitutive model is employed to determine the stress-strain behaviour of concrete under uniaxial compression, and the calculated results are compared with the experimental results under different high temperature levels. Results indicate that the proposed model can not only predict the stress-strain behaviour with acceptable accuracy in macroscopic scale, but also reveal the damage evolution mechanism in mesoscopic scale. Finally, the constitutive behaviour under biaxial compression is also simulated to investigate the influence of high temperature on biaxial stress-strain behavior and strength envelope. Citation: International Journal of Damage Mechanics PubDate: 2022-06-10T04:35:25Z DOI: 10.1177/10567895221095610
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Authors:Liu Jin, Kaixin Liu, Renbo Zhang, Wenxuan Yu, Xiuli Du, Xiaofang Deng Abstract: International Journal of Damage Mechanics, Ahead of Print. Concrete structures in extremely cryogenic environments may be subject to dynamic loadings as a result of occasional accidents or terrorist attacks during the service life. Considering the cryogenic temperature effect and strain rate effect of each phase for concrete, a meso-scale numerical model of the concrete subjected to cryogenic temperature and dynamic loadings was presented in this study, which serves as a preliminary foundation for calculating and evaluating the performances of concrete structures at cryogenic temperature. Taking concrete cube as an example, the dynamic compressive behavior and strain rate effect of concrete specimens at cryogenic temperature from 20 °C to –160 °C were modelled and investigated. The numerical results indicate that the failure appearances and compressive strength are highly related to the cryogenic temperature and dynamic loadings. The compressive strength at cryogenic temperature is greater than that at ambient temperature, and the sensitivity of dynamic compressive strength to strain rate is enhanced at cryogenic temperature. Moreover, the absorbed energy and dynamic elastic modulus tend to increase with the decrease of temperature and increase of strain rate. According to the numerical results, an empirical formula on dynamic increase factor of compressive strength at cryogenic temperatures (CDIFT) was established. Citation: International Journal of Damage Mechanics PubDate: 2022-06-08T08:07:27Z DOI: 10.1177/10567895221105590
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Authors:Ruiqiang Zhang, Zhusheng Shi, Victoria A Yardley, Jianguo Lin Abstract: International Journal of Damage Mechanics, Ahead of Print. Forming limit curves (FLCs), which are constructed using the limit strains at localised necking, are the most widely used tools for the evaluation of the formability of sheet metals. Fracture forming limit curves (FFLCs) are more recently developed, complementary tools for formability evaluation which are instead constructed using the limit strains at fracture. Since the formability depends strongly on forming conditions such as strain state, temperature and strain rate, models for predicting FLCs and FFLCs are essential for the optimisation and further application of hot forming processes in which these forming conditions vary significantly with both position and time. However, no model has so far been developed to predict FFLCs either alone or in conjunction with FLCs for sheet metals such as boron steel under hot stamping conditions. In this study, a set of unified viscoplastic constitutive equations for the prediction of both FLCs and FFLCs based on continuum damage mechanics (CDM) has been formulated from a set of recently developed constitutive equations for dislocation-based hardening, in combination with two novel coupled variables characterising the accumulated damage leading to localised necking and fracture. The novel variables take into account the effects of strain state, temperature and strain rate on the formability of sheet metals. The material constants in the CDM-based constitutive equations have been calibrated using experimental data comprising true stress-true strain curves and limit strains of a 22MnB5 boron steel obtained at a range of temperatures and strain rates. Investigation of the effect of varying selected parameters in the coupled damage variables on the resulting computed FLCs and FFLCs has demonstrated the flexibility of the model in enabling curves of different shapes and numerical values to be constructed. This indicates the potential of the CDM-based constitutive model for application to other materials for warm or hot stamping processes. Citation: International Journal of Damage Mechanics PubDate: 2022-06-06T04:27:37Z DOI: 10.1177/10567895221105655
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Authors:Jing Long, Feng Xu, Yuanyuan Wu, Yousong Xue, Baozhong Sun, Bohong Gu, Wei Zhang Abstract: International Journal of Damage Mechanics, Ahead of Print. Ageing conditions and braided structures will affect dynamic damage and failure mechanisms of 3D braided composites. Here we report the influence of thermo-oxidative ageing on impact compression behaviors of 3D braided composite with and without axial yarns, i.e., four directional (3D4d) and five directional (3D5d) braided composites. We found a significant difference in mechanical properties between epoxy resins and composites after ageing. The impact compressive strength of epoxy resins declined rapidly and then slowly, while the composites decreased continuously, with the increase of ageing days. The interfacial debonding is main degradation mechanism for both braided composites at the later ageing stage. Thermo-oxidative ageing accelerates the inner damage evolution which propagates from surface cracks. Compared with 3D4d braided composites, the 3D5d braided structure has higher strength retaining level after ageing. In addition, the 3D5d braided samples have higher resistance to impact deformation and lower crack propagation. Finite element analysis (FEA) results revealed that 3D5d composites showed higher load carrying capacity and less damages than 3D4d composites. Citation: International Journal of Damage Mechanics PubDate: 2022-06-02T04:20:43Z DOI: 10.1177/10567895221099666
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Authors:Mitul Sisodiya, Yida Zhang Abstract: International Journal of Damage Mechanics, Ahead of Print. We present a novel microcrack-damage theory for brittle solids under compression. Instead of using internal variables like zeroth, second or fourth rank damage tensors, the state of material damage is represented by an internal function that encapsulates the information of direction, density and size of microcracks. Just like other internal variables, the evolution of this state function must obey the second law of thermodynamics for arbitrary loading paths. This is done by casting the model in the framework of continuous hyperplasticity and enforcing a non-negative dissipation rate functional. The proposed framework offers predictions on the continuous evolution of microcrack density and the induced material anisotropy along with the macroscopic stress-strain curves. The use of continuous damage function grants the model significantly enhanced resolution in characterizing the direction-dependent response of cracked solids compared to classical models that are based on damage tensors. Two scenarios are considered in developing the theory, one assumes frictionless cracks and the other incorporates friction between crack surfaces. The results highlight that inelasticity, pressure dependence, and loading-unloading hysteresis exhibited by brittle solids are natural consequences of frictional microcracks. The proposed theory offers a generic and versatile framework to upscale micromechanical processes operating at individual crack scale to explain the macroscopic behavior of cracked solids. Citation: International Journal of Damage Mechanics PubDate: 2022-05-12T05:49:08Z DOI: 10.1177/10567895221095890
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Authors:Tingwei Chen, Jiankang Chen, Jinhan Chen Abstract: International Journal of Damage Mechanics, Ahead of Print. For plain concrete materials, the degradation of concrete by seawater is mainly reflected in the corrosion of sulfate ions. In this study, the variation in the flexural strength of concrete specimens with different water-cement ratios under different sulfate concentrations for 470 days is explored, and the effect of sulfate environment on the decay of flexural strength of concrete with corrosion time is experimentally examined. The results show that the evolution of flexural strength can be divided into three stages: strength attenuation stage, strength recovering stage and strength re-attenuation stage. According to the experimental results, the mechanism of strength attenuation, rebound and re-attenuation is established. Combining the chemical reaction rate equations of continued hydration, delayed growth of ettringite and growth of hydroxy-AFm, a new model for the flexural strength degradation of concrete under sulfate corrosion is proposed. Further, the influence of water-cement ratio and corrosive sulfate solution concentration on the flexural strength of concrete is analyzed. Since the ability of concrete to resist sulfate corrosion can be different for different corrosion systems, a unified method is proposed for evaluating the sulfate corrosion resistance of concrete. Citation: International Journal of Damage Mechanics PubDate: 2022-05-06T07:11:38Z DOI: 10.1177/10567895221095888
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Authors:Yang Wang, Guo-Qin Sun, Jinfeng Liu, Xiaodong Liu, Deguang Shang Abstract: International Journal of Damage Mechanics, Ahead of Print. Multiaxial high-cycle fatigue failure criterion and life prediction is important for structural components under complex low stress. A new multiaxial high-cycle fatigue damage parameter based on the plane of maximum shear stress is proposed, which includes the maximum shear stress amplitude, normal stress amplitude and maximum equivalent normal stress. The maximum equivalent normal stress is defined in the form of SWT stress function considering the influence of mean stress. The feasibility of the proposed failure criterion and life prediction model is verified by test data of different materials. The predicted results show that the life prediction error of the proposed fatigue model is basically within three times by comparing with McDiarmid, Matake, Crossland and Papadopoulos fatigue models. Citation: International Journal of Damage Mechanics PubDate: 2022-04-29T05:42:18Z DOI: 10.1177/10567895221091308
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Authors:A Karimzadeh, S S R Koloor, M Petrů, MR Ayatollahi, MY Yahya Abstract: International Journal of Damage Mechanics, Ahead of Print. In orthodontic treatments, mechanical characterization of orthodontic bracket bonded to the tooth is essential to determine the bond strength and mechanical behavior of the bracket-adhesive-tooth system. In this study, the linear-nonlinear mechanical behavior and damage characterization of Filtek Z350 XT (3M ESPE) nanocomposite as a dental adhesive material to bond orthodontic brackets to tooth enamel, are investigated using numerical and experimental methods. Full sets of tensile, shear, and mixed modes I/II and I/II/III debonding experiments are conducted to extract the mechanical properties of the nanocomposite adhesive as the bracket/tooth interface. The results of the experiments are used to obtain the cohesive law and the damage model parameters. Three-dimensional finite element models of the bracket debonding tests are developed, while the cohesive zone model (CZM) is used to define the constitutive behavior of the nanocomposite interface under the tensile, shear, and mixed-mode loading conditions. The FE results showed a good correlation with the measured data, indicated the validity of the constitutive model, damage properties, and simulation process. The bond strengths of the nanocomposite adhesive are obtained 8.35 and 4.12MPa in modes I and II loadings, respectively. Citation: International Journal of Damage Mechanics PubDate: 2022-04-29T05:35:53Z DOI: 10.1177/10567895221088027
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Authors:Smojver Ivica, Ivančević Darko, Brezetić Dominik, Haramina Tatjana Abstract: International Journal of Damage Mechanics, Ahead of Print. In this work, a constitutive model of an intrinsically self-healing composite matrix material is presented. The developed model comprises a micro-damage initiation and evolution model, and a healing evolution model, which are combined with the von Mises linear isotropic hardening plasticity. It is implemented into the Abaqus/Standard user material subroutine UMAT and validated using experimental results of static tensile and two-cycle tensile tests performed on partially neutralised poly(ethylene-co-methacrylic acid) (EMAA) ionomer copolymer, Surlyn® 8940. In the development of the model, Continuum Damage Healing Mechanics (CDHM) concepts of nominal and healing configurations are used. In addition, these concepts are used along with the strain equivalence hypothesis to streamline the numerical implementation. The strain equivalence hypothesis relates strain and stress tensors in the nominal and the healing configuration. Finally, successful validation has shown that the developed model is able to accurately predict behaviour of Surlyn® 8940 coupons during tensile tests and it can precisely predict the accumulation of plastic strain. Citation: International Journal of Damage Mechanics PubDate: 2022-04-21T04:52:02Z DOI: 10.1177/10567895221095609
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Authors:Sajad Alimirzaei, Mehdi Ahmadi Najafabadi, Ali Nikbakht, Lotfollah Pahlavan Abstract: International Journal of Damage Mechanics, Ahead of Print. The focus of this study is to investigate the mechanical properties, of ±35° and ±55° filament wound (FW) composite tubes under axial compression loading using the acoustic emission technique. For this purpose, material failure, crashworthiness characteristics, and the effect of each mechanism on the energy absorption capacity were studied using numerical and experimental approaches. Also, to identify and estimate the contribution percentage of damage mechanisms as well as how the damage grows in the specimens, the analysis of acoustic emission signals recorded during loading was performed. Digital image correlation was additionally used to capture displacement/strain contour maps. Finally, to analyze the effect of the winding pattern in the experimental test, the tubes were simulated using finite element analysis (FEA). For modeling of damage mechanisms, a 3D continuum damage model was used. The results of signal processing showed that by increasing the weaving angle of fibers from ±35° to ±55°, the separation of fibers from the matrix decreases, and the percentage of matrix crushing and fiber failure increases. The assessment of damage percentages showed that the reason for the large drop in force at ±55° compared to ±35° is the increase in matrix crushing. Furthermore, the failure behavior of FW tubes appeared to be dominated by local buckling, and the FEA effectively predicted the linear behavior and maximum load value of the composite tubes. Citation: International Journal of Damage Mechanics PubDate: 2022-04-21T04:45:52Z DOI: 10.1177/10567895221095603
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Authors:Y Wang, JQ Han, ZY Song, C Zhu Abstract: International Journal of Damage Mechanics, Ahead of Print. Rock mass is often encountered with complicated stress disturbance caused by human-induced engineering loads and the environmental loads. Cyclic or fatigue loading path with fixed loading frequency are widely performed. To date, however, damage and fracture evolution of the pre-flawed rock under variable-frequency multi-level constant amplitude (VFMLCA) cyclic loads was not well understood. In the present study, granite samples containing a circular hole and two fissures were prepared to conduct VFMLCA cyclic loading tests. The fatigue strength, deformation, energy conversion, damage propagation, and crack coalescence were comprehensively investigated. Testing results show that the fatigue strength increases with increasing fissure angle. Rock volumetric strain and the dissipated energy are the maximum for rock with a 50° fissure angle. The dissipated energy increases with decreasing of loading frequency and an exponential relation is revealed between them. In addition, a damage evolution model that can well describe the two-stage and three-stage damage evolution for each cyclic loading level and the entire loading process is proposed and proved. Moreover, three failure modes of single tensile coalescence, double tensile coalescence, and double shear coalescence were revealed from the reconstructed CT images. It is suggested that the double shear coalescence is prone to forming large crack network. Citation: International Journal of Damage Mechanics PubDate: 2022-04-19T06:05:02Z DOI: 10.1177/10567895221095889
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Authors:Yun-Fei Fu, Johannes Reiner Abstract: International Journal of Damage Mechanics, Ahead of Print. This paper presents a systemic calibration methodology to efficiently simulate progressive damage evolution in four different pultruded glass fiber reinforced polymer (GFRP) composites using the strain-based COMposite DAMage Model (CODAM2) in the commercial finite element software LS-DYNA. In particular, Compact Tension (CT), scaled-up CT, and wide CT tests are simulated to find the best set of input parameters by considering four distinct indicators obtained from experimental and numerical load vs displacement data. By combining these indicators into a physically meaningful equivalent deviation value via a linear weighted-sum method, the results show that the most suited input damage variables yield physically accurate crack length predictions which underlines the robustness and accuracy of the proposed method. Furthermore, it is shown that the incorporation of bi-linear softening laws improves CODAM2 simulation results by up to 90%, however it also increases the number of parameters to be calibrated. Citation: International Journal of Damage Mechanics PubDate: 2022-04-12T04:41:11Z DOI: 10.1177/10567895221089655
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Authors:Tubing Yin, Zheng Yang, You Wu, Xiaosong Tan, Mingjian Li Abstract: International Journal of Damage Mechanics, Ahead of Print. The stability of rock mass after fire is a concern of many engineering projects. In this paper, the effects of open fire and different cooling methods on granites were investigated. The static Brazilian test, dynamic Brazilian test, and P-wave velocity test were carried out to evaluate the mechanical properties and damage evolution behavior. A high-speed camera is employed to monitor the failure process of rock. The microstructures of the treated granites were observed by scanning electron microscope (SEM). The results showed that the fire duration and cooling treatment have a significant effect on the P-wave velocity, static nominal tensile strength, and dynamic nominal tensile strength of granite. These characteristics decrease rapidly during 0 to 10 min, and slowly decrease after 20 min. Compared to the air-cooling treatment, the water-cooling treatment has greater damage to the heated granite. To better understand the results, the rapid heating process of open fire heating was simulated using Abaqus software. The results reveal that there is a thinner compressive stress zone at the bottom of the specimen, and there is a large zone in the middle of the sample with higher tensile stress. The crack extension would be expanded due to high tensile stress, leading to the reduction of the tensile strength of the rock. This paper aims to better predict the degree of damage of rock materials after actual fire, as well as preliminarily explore the effect of the fire exposure duration and fire extinguishing method on the tensile properties of rock. Citation: International Journal of Damage Mechanics PubDate: 2022-04-11T07:11:11Z DOI: 10.1177/10567895221092168
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Authors:Wei Su, Hongmei Zhu First page: 957 Abstract: International Journal of Damage Mechanics, Ahead of Print. 2198-T8 aluminum-lithium alloy is an advanced aeronautical engineering material. The multiaxial fatigue tests of notched specimens are conducted with the variables of notch diameter, notch number, and equivalent stress amplitude, respectively. The strain field and fatigue life are characterized and calculated by digital image correlation (DIC) technique. The results show that: the fatigue life decreases with the increase of notch diameter, number of notches, and the equivalent stress amplitude. The strain curves calculated by VIC-3D are similar to those obtained by the testing. The normal and shear strain concentration becomes obvious at 80% to 90% fatigue life, and the surface cracks appear at 95% fatigue life, typical multiaxial fatigue morphologies including tire patterns and wear fatigue striations are observed on the fracture surface. The feasibility of the DIC technique to characterize multiaxial fatigue behavior is verified. The modified SWT model provides fine life prediction results with all predicted data within a factor of two. Citation: International Journal of Damage Mechanics PubDate: 2022-03-07T05:31:53Z DOI: 10.1177/10567895211066337
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Authors:Haopeng Jiang, Annan Jiang, Fengrui Zhang, Xiurong Yang First page: 975 Abstract: International Journal of Damage Mechanics, Ahead of Print. The repeated action of high temperature and water cooling will have a strong deteriorating effect on the mechanical properties of the rock, which will eventually lead to the damage and cracking of the rock. In order to study the influence of heating and water-cooling cycles on rocks, the P-wave velocity and mechanical properties of red sandstone after heating and water-cooling cycles were tested. Meanwhile, based on the Weibull distribution theory, a statistical damage constitutive model based on Mohr-Coulomb strength criterion considering the effects of heating and water-cooling cycles was established, and verified based on the results of triaxial tests. The results show that the P-wave velocity and peak intensity decrease with the temperature under the same number of cycles. The elastic modulus will decrease with the temperature and the number of cycles, indicating that the red sandstone will gradually soften and the ductility will increase under repeated high temperature and water-cooling cycles. And the model can well reflect the stress-strain curves of different high temperature and water-cooling cycles. The research results can provide analytical theories and methods for geothermal development projects. Citation: International Journal of Damage Mechanics PubDate: 2022-03-12T07:11:49Z DOI: 10.1177/10567895221087714
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Authors:Zhaohui Chong, Qiangling Yao, Xuehua Li, Lun Yan, Fengsheng Su First page: 999 Abstract: International Journal of Damage Mechanics, Ahead of Print. Transforming intact coal seams into broken coals that are convenient to transport is one of the technical problems of fluidized coal mining. In this paper, cyclic freeze-thaw by liquid nitrogen (CFT-LN2) was adopted to improve the fragmentation degree of coal seams. The coal pore structure evolutions and coal breakage properties were explored using the acoustic emission (AE) parameter method (the kernel density estimation method), the fractal theory, and the nuclear magnetic resonance spectra. The main factors discussed include the number of freeze-thaw cycles, the LN2 freezing time and the moisture content of the coal sample. Variations of these factors alter the mechanical and physical characteristics and pore structures of coal samples treated with CFT-LN2. The results reveal that the kernel density estimation method can distinguish the density region determined based on the rise angle (RA) and average frequency (AF) values and visualize the rupture modes of coal samples formed after CFT-LN2. As the number of freeze-thaw cycles grows, the tensile rupture mode gradually transits to shear rupture mode; the fractal dimension gradually increases; the equivalent average size gradually decreases; and the mass of different fragment sizes tend to be more uniform. Only freezing in LN2 without CFT-LN2 cannot notably change the rupture mode or fragmentation degree of a coal sample. During CFT-LN2, the coal matrix is subjected to repeated action of contraction in LN2 and expansion at room temperature. As a result, new micro-pores are formed easily in the matrix, and micro-pores incline to connect into larger pores. Meanwhile, increasing the moisture content is conducive to coal fracturing through CFT-LN2. Citation: International Journal of Damage Mechanics PubDate: 2022-03-16T04:50:40Z DOI: 10.1177/10567895221087716
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Authors:Dongping Zhu, Wei Zhang, Zhixia Ding First page: 1027 Abstract: International Journal of Damage Mechanics, Ahead of Print. A modified fatigue damage model is proposed considering the loading sequence effect under variable amplitude loading conditions. The transition sequence is obtained from the counting sequence by an equivalent rainflow counting method and is used to provide the loading sequence information for fatigue damage accumulation prediction. Rainflow counting matrix and sequence transition matrix are formulated based on the rainflow counting sequence and the transition sequence. The relation between the two matrices and the original loading sequence is evaluated in detail. In the deterministic fatigue estimation, the rainflow counting matrix and the sequence transition matrix are integrated into the proposed modified damage model based on the linear damage rule. Mean stress transition is applied to the rainflow counting matrix for loading level effect. Existing experimental data are used to validate the fatigue damage estimation from the deterministic framework. In order to evaluate the fatigue under random loading conditions, the rainflow counting matrix and sequence transition matrix are mapped to one-dimensional exponential and Laplace distributions based on the stationary random process. Numerical simulation is conducted to validate the proposed mapping distributions. Meanwhile, the impact of the correlation length on the proposed distributions under stationary random loading sequence is investigated as well. Finally, with the given distributions of the rainflow counting matrix and sequence transition matrix, a reconstruction procedure is simulated and discussed for probabilistic fatigue estimation. The proposed model provides a sophisticated approximation to the original loading sequence with a sequence transition effect. The proposed modified fatigue damage model corrects the deficiencies of the linear damage rule with sufficient sequence information from the originally applied loading. Furthermore, the probabilistic fatigue estimation can evaluate the accumulated fatigue damages under a random loading process with the sequence transition effect. Citation: International Journal of Damage Mechanics PubDate: 2022-03-18T11:33:45Z DOI: 10.1177/10567895221088029
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Authors:Tongzhou Gao, Yang Tong, Zhixin Zhan, Weiwei Mei, Weiping Hu, Qingchun Meng First page: 1057 Abstract: International Journal of Damage Mechanics, Ahead of Print. In this study, a non-local approach is developed for the fatigue life prediction of notched specimens, considering stress/strain gradient and elastic-plastic fatigue damage. The damage coupled constitutive models are presented to model the mechanical behavior of material. The critical plane method and triaxiality factor are employed to determine the location of the couple point. The gradient values of mechanical quantities are then computed, and the modified coefficients in damage models are acquired. The numerical simulations are implemented to compute the damage evolution process and predict fatigue life. Meanwhile, the coupling effects between stress field and damage field are considered. The predicted results are verified by experimental data, and also compared with the local method. Finally, the influence of stress concentration factor, shape of notch, and cyclic variation of stress/strain gradient are further investigated. Citation: International Journal of Damage Mechanics PubDate: 2022-03-25T08:55:22Z DOI: 10.1177/10567895221089663
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Authors:Yang Tang, Hailong Zhang, Xiaoxiao Guo, Ting Ren First page: 1082 Abstract: International Journal of Damage Mechanics, Ahead of Print. Digital-image correlation (DIC) is a deformation-measurement technique used to determine rock and soil mechanics. We review DIC tests of rock and soil, with data categorized according to specimen shape, test type, and DIC method. A new three-dimensional-DIC system integrates a transparent triaxial-compression servo-control test system for rocks. The confining pressure cell is transparent and three groups of image-acquisition units, which can be controlled with loading cell at the same time, are adopted to obtain the maximum observed fields. The average magnification factors caused by the transparent cell and oil are 1.4430 and 1.0331 for the measured horizontal and vertical distances, respectively. A triaxial compressive test of rock is performed and the specimen’s surface-strain fields and crack propagation are discussed. Citation: International Journal of Damage Mechanics PubDate: 2022-03-28T10:04:39Z DOI: 10.1177/10567895221089660
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Authors:Yao Zhang, Shaoqi Zhang, Qing Chen, Yi Shen, J Woody Ju, Mathieu Bauchy First page: 1096 Abstract: International Journal of Damage Mechanics, Ahead of Print. When subjected to fires, cementitious composites can be seriously damaged. However, the mechanical behavior of nanoscale calcium silicate hydrate (C–S–H) grains, which are the main binder of cementitious composites, exposed to elevated temperatures under shear deformations remain poorly investigated. In this paper, considering different calcium/silicate (C/S) molar ratios (i.e., C/S = 1.10, 1.33, and 1.64), the shear behavior of the C–S–H grain after exposure to different high-temperature levels (i.e., 300 K, 500 K, 700 K, 900 K, and 1000 K) is studied by conducting series of reactive molecular dynamics simulations. Results reveal that the C–S–H grain exhibits good plasticity under shear deformation. Furthermore, the shear modulus of the C–S–H grain is between 14 GPa and 17 GPa and exhibits a decrease with the calcium/silicon (C/S) molar ratio at ambient temperature. While the shear strength is around 1.0 GPa and reaches the lowest value at C/S = 1.64. Interestingly, we report that heating can lead to the increase of the shear modulus and shear strength due to the sevaporation of the interlayer water which generally acts as the lubricant. Additionally, we show that heating has no clear influence on the shear strain corresponding to the onset of yielding when the C/S ratio is high but can indeed improve the shear strain corresponding to the shear strength. Furthermore, the yielding area of the C–S–H grain under the shear deformation can be enlarged. Finally, factors affecting the strength degradation of cementitious composites after being heated to different temperature levels are further discussed based on the simulation results. Citation: International Journal of Damage Mechanics PubDate: 2022-04-11T07:16:40Z DOI: 10.1177/10567895221093395
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