Artykuły w czasopismach: „Visco-plastic Damage Model”

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Wang, Ru Bin, Wei Ya Xu i Jiu Chang Zhang. "Modeling Coupled Flow-Stress-Damage during Creep Deformation". Applied Mechanics and Materials 204-208 (październik 2012): 3294–98. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.3294.

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In order to reflect the tertiary rheological characteristics of hard rocks at the high stress states, a new nonlinear visco-elastic-plastic model is proposed on the basis of linear visco-elastic-plastic model and nonlinear visco-elastic-plasticity. And then the corresponding constitutive model are deduced, which can be used for describing rocks’ long-term strength characteristics and their creep deformational behavior and time-dependent damage under interaction of coupled seepage-stress field in rock engineering. At last, considering the time effect of rock damage in the process of tertiary creep, a coupled seepage -stress creep damage model for investigating the whole creep deformation behavior, including tertiary creep failure process is established, and the related equations governing the evolution of stress, creep damage and rock permeability along with the creep deformation of rock is introduced.

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Staub, C., i J. C. Boyer. "An orthotropic ductile damage model for visco-plastic materials". Journal of Materials Processing Technology 60, nr 1-4 (czerwiec 1996): 297–304. http://dx.doi.org/10.1016/0924-0136(96)02345-x.

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Wang, X. C., i A. M. Habraken. "An Elastic-Visco-Plastic Damage Model : From Theory to Application". Le Journal de Physique IV 06, nr C6 (październik 1996): C6–549—C6–558. http://dx.doi.org/10.1051/jp4:1996655.

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Wang, Xingkai, Leibo Song, Caichu Xia, Guansheng Han i Zheming Zhu. "Nonlinear Elasto-Visco-Plastic Creep Behavior and New Creep Damage Model of Dolomitic Limestone Subjected to Cyclic Incremental Loading and Unloading". Sustainability 13, nr 22 (9.11.2021): 12376. http://dx.doi.org/10.3390/su132212376.

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For many rock engineering projects, the stress of surrounding rocks is constantly increasing and decreasing during excavating progress and the long-term operation stage. Herein, the triaxial creep behavior of dolomitic limestone subjected to cyclic incremental loading and unloading was probed using an advanced rock mechanics testing system (i.e., MTS815.04). Then, the instantaneous elastic strain, instantaneous plastic strain, visco-elastic strain, and visco-plastic strain components were separated from the total strain curve, and evolutions of these different types of strain with deviatoric stress increment were analyzed. Furthermore, a damage variable considering the proportion of irrecoverable plastic strain to the total strain was introduced, and a new nonlinear multi-element creep model was established by connecting the newly proposed damage viscous body in series with the Hookean substance, St. Venant body, and Kelvin element. The parameters of this new model were analyzed. The findings are listed as follows: (1) When the deviatoric stress is not more than 75% of the compressive strength, only instantaneous deformation, transient creep, and steady-state creep deformation occur, rock deformation is mainly characterized by the instantaneous strain, whereas the irrecoverable instantaneous plastic strain accounts for 38.02–60.27% of the total instantaneous strain; (2) Greater deviatoric stress corresponds to more obvious creep deformation. The visco-elastic strain increases linearly with the increase of deviatoric stress, especially the irrecoverable visco-plastic strain increases exponentially with deviatoric stress increment, and finally leads to accelerated creep and delayed failure of the sample; (3) Based on the experimental data, the proposed nonlinear creep model is verified to describe the full creep stage perfectly, particularly the tertiary creep stage. These results could deepen our understanding of the elasto-visco-plastic deformation behavior of dolomitic limestone and have theoretical and practical significance for the safe excavation and long-term stability of underground rock engineering.

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Pedersen, R. R., A. Simone i L. J. Sluys. "An analysis of dynamic fracture in concrete with a continuum visco-elastic visco-plastic damage model". Engineering Fracture Mechanics 75, nr 13 (wrzesień 2008): 3782–805. http://dx.doi.org/10.1016/j.engfracmech.2008.02.004.

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KANG, GUOZHENG, JUN DING i YUJIE LIU. "DAMAGE-COUPLED CONSTITUTIVE MODEL FOR UNIAXIAL RATCHETING AND FATIGUE FAILURE OF 304 STAINLESS STEEL". International Journal of Modern Physics B 22, nr 31n32 (30.12.2008): 5419–24. http://dx.doi.org/10.1142/s0217979208050590.

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Based on the existed experimental results of 304 stainless steel, the evolution of fatigue damage during the stress-controlled cyclic loading was discussed first. Then, a damage-coupled visco-plastic cyclic constitutive model was proposed in the framework of unified visco-plasticity and continuum damage mechanics to simulate the whole-life ratcheting and predict the fatigue failure life of the material presented during the uniaxial stress-controlled cyclic loading with non-zero mean stress. In the proposed model, the whole life ratcheting was described by employing a non-linear kinematic hardening rule, i.e., the Armstrong-Frederick model combined with the Ohno-Wang model I, and considering the effect of fatigue damage. The damage threshold was employed to determine the failure life of the material. The simulated whole-life ratcheting and predicted failure lives are in a fairly good agreement with the experimental ones of 304 stainless steel.

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Lee, Chi Seung, Myung Hyun Kim, Min Sung Chun, Tak Kee Lee i Jae Myung Lee. "Fatigue Damage Model for Numerical Assessment of Fatigue Characteristics". Materials Science Forum 580-582 (czerwiec 2008): 663–66. http://dx.doi.org/10.4028/www.scientific.net/msf.580-582.663.

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The aim of this study is the development of a numerical technique applicable for the fatigue assessment based on the damage mechanics approach. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed in order to numerically evaluate the material fatigue responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations, are derived. The performance of the developed technique has been verified using the S-N relationship assessment for STS304 stainless steel.

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Rahaman, Md Masiur, Abhishek Pathak i Debasish Roy. "A thermo-visco-plastic damage model and SPH simulations of plugging failure". Mechanics of Advanced Materials and Structures 25, nr 15-16 (17.03.2017): 1374–82. http://dx.doi.org/10.1080/15376494.2017.1286419.

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Wang, Qing-duo, Feng-hai Yu, Aleksei Renev, Sergei Tsibaev i Xue-rui Yang. "The analysis of rheological damage of anchorage body based on visco-elasto-plastic model". E3S Web of Conferences 303 (2021): 01060. http://dx.doi.org/10.1051/e3sconf/202130301060.

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In order to study the rheological damage of anchorage body, rheological damage model of anchorage body is established in this paper, and it is based on visco-elasto plastic model that is often used to simulate rock rheological characteristics. The expressions of creep constitutive equation and elastic modulus of anchorage body are obtained through the analysis of rheological damage model of anchorage body, and by the fitting calculation results, finding that the theoretical creep curve is matched with the experimental creep curve under certain conditions. The research conclusions have critical significance to the bolting support and design.

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Luo, Yan, i Qing Gao. "A Damage-Coupled Time-Dependent Multi-Axial Fatigue Failure Model for Solder Alloy 63Sn-37Pb". Applied Mechanics and Materials 128-129 (październik 2011): 361–66. http://dx.doi.org/10.4028/www.scientific.net/amm.128-129.361.

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Based on the time-dependent deformation behavior of solder alloy 63Sn-37Pb at room temperature, a damage-coupled unified visco-plastic multi-axial fatigue model and its failure criterion were proposed. In the evolution equation of damage for the model, the time-dependent effect of damage was taken into account. The model was used to predict the fatigue life under different loading paths. The comparison between the predicted and experimental results demonstrated that the time-dependent failure model can simulate the deformation behavior and predict the fatigue life well under different nonproportional strain paths.

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Kim, Kunhwi, John E. Bolander i Yun Mook Lim. "Rigid-Body-Spring Network with Visco-Plastic Damage Model for Simulating Rate Dependent Fracture of RC Structures". Applied Mechanics and Materials 82 (lipiec 2011): 259–65. http://dx.doi.org/10.4028/www.scientific.net/amm.82.259.

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The mechanical properties of concrete materials vary with the loading rate underdynamic conditions, which can inﬂuence the dynamic fracture behavior of structures. The ratedependency is reported as due to the microscopic mechanisms, such as a material inertia eﬀectand the Stefan eﬀect. In this study, the rigid-body-spring network (RBSN) is employed forthe fracture analysis, and the visco-plastic damage model is implemented to represent the rateeﬀect in this macroscopic simulation framework. The parameters in the Perzyna type visco-plastic formulation are adjusted through the direct tensile test with various loading rates asa preliminary calibration. As the loading rate increases, the strength increase is presented interms of the dynamic increase factor (DIF), and compared with the experimental and empiricalresults. Next, the ﬂexural beam test is conducted for plain and reinforced concrete beams underslow and impact rates of loading. At the failure stage, diﬀerent crack patterns are observeddepending on the loading rate. The impact loading induces the failure to be more localizedon the compressive zone of the beam, which is due to rather the rate dependent materialfeatures. In structural aspects, the reinforcement exerts stronger eﬀects on reducing crack widthand improving ductility at the slow loading rate. The ductility is also evaluated through thecomparison of load-deformation curves until the ﬁnal rupture of the beams. This study canprovide understandings of the structural rate dependent behavior and the reinforcing eﬀectunder dynamic loadings.

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Kang, Guozheng, Yujie Liu, Jun Ding i Qing Gao. "Uniaxial ratcheting and fatigue failure of tempered 42CrMo steel: Damage evolution and damage-coupled visco-plastic constitutive model". International Journal of Plasticity 25, nr 5 (maj 2009): 838–60. http://dx.doi.org/10.1016/j.ijplas.2008.06.004.

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Suzuki, Jorge, Yongtao Zhou, Marta D’Elia i Mohsen Zayernouri. "A thermodynamically consistent fractional visco-elasto-plastic model with memory-dependent damage for anomalous materials". Computer Methods in Applied Mechanics and Engineering 373 (styczeń 2021): 113494. http://dx.doi.org/10.1016/j.cma.2020.113494.

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Gui, Zhong-xiang, Xiao Hu i Zi-jian Wang. "An elasto-visco-plastic constitutive model of polypropylene incorporating craze damage behavior and its validation". Journal of Central South University 24, nr 6 (czerwiec 2017): 1263–68. http://dx.doi.org/10.1007/s11771-017-3530-9.

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Münstermann, Sebastian, Pawel Kucharczyk, Georg Golisch i Benedikt Döbereiner. "Phenomenological Modelling of Impact Toughness Transition Behaviour". Applied Mechanics and Materials 784 (sierpień 2015): 27–34. http://dx.doi.org/10.4028/www.scientific.net/amm.784.27.

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The toughness transition behavior of ferritic steel results from the fact that two competing fracture mechanisms can be activated independently or progressively. Temperature, strain rate and the material ́s hardening properties are the major influences affecting the result of this competition between cleavage and ductile fracture mechanisms. An elastic visco-plastic plasticity model with stress-state dependent yielding and isotropic hardening forms the basis of a model to predict the Charpy impact toughness properties of steels with bcc crystal structure for transition behavior. A scalar damage variable is coupled into the yield potential in order to capture the effects of damage induced softening. The corresponding damage evolution law considers damage initiation criteria for both mentioned fracture mechanisms. Material parameter identifications and successful model application in terms of Charpy impact toughness tests are demonstrated.

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Frija, Mounir, Raouf Fathallah i T. Hassine. "Finite Element Prediction of Laser Shock Peened Surface Modifications in Ti-6Al-4V Alloy". Key Engineering Materials 417-418 (październik 2009): 853–56. http://dx.doi.org/10.4028/www.scientific.net/kem.417-418.853.

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This paper presents a numerical simulation of the Laser Shock Peening process (LSP) using ﬁnite element method. The majority of the controlling parameters of the process have been taken into account. The laser loading has been characterised by using a repetitive time Gaussian increment pressure applied uniformly at circular impacted zone. The behavior of the subjected material is supposed to be elasto-visco-plastic coupled with damage using the Johnson Cook law with his shear failure model. The proposed model leads to obtain the surface inducing modifications, which are classified in this work into three categories: (i) the in-depth residual stress profile, (ii) the induced plastic strains profile and (iii) also the superficial damage which can be induced in few cases where the operating conditions are not well chosen. An application on a laser shock peened super alloy Ti-6Al-4V has been carried out. The comparison of the residual stresses, obtained by X-ray diffraction method and by ﬁnite element calculation, shows a good correlation.

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Darbha, K., J. H. Okura i A. Dasgupta. "Thermomechanical Durability Analysis of Flip Chip Solder Interconnects: Part 1—Without Underfill". Journal of Electronic Packaging 121, nr 4 (1.12.1999): 231–36. http://dx.doi.org/10.1115/1.2793845.

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A generalized multi-domain Rayleigh-Ritz (MDRR) approach developed by Ling and Dasgupta (1995), is extended in this paper, to obtain the stress field in flip chip solder interconnects, under cyclic thermal loading. Elastic, Plastic and time-dependent visco-plastic analysis is demonstrated on flip chip solder interconnects. The method has been applied to other surface-mount interconnects in the past such as J-lead (Ling and Dasgupta, 1996a) and ball-grid joints (Ling and Dasgupta, 1997). The analysis results for the J-lead and ball grid joints have confirmed that the MDRR technique is capable of providing stress-strain hysteresis with adequate accuracy, at a fraction of the modeling effort required for finite element model generation and analyses. Nonlinear viscoplastic stress analysis results for flip chip interconnects without underfill are presented in this paper. The fatigue endurance of the solder joints is assessed by combining results from this stress analysis model with an energy-partitioning damage model (Dasgupta et al., 1992). The life predicted by the analytical damage model is compared with experimental results.

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YOSHIDA, Junji, i Toshiyuki SUGIYAMA. "A HYPERELASTIC VISCO-ELASTO-PLASTIC DAMAGE MODEL FOR RUBBER-LIKE SOLIDS INCLUDING STRAIN-DEPENDENCY OF HYSTERETIC LOOPS". Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)) 71, nr 1 (2015): 14–33. http://dx.doi.org/10.2208/jscejam.71.14.

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Alwar, R. S., P. Chellapandi i S. B. Bhoje. "Assessment of Life of Inner Vessel for a Pool-Type Fast Breeder Reactor Based on Inelastic and Viscoplastic Deformations". Journal of Pressure Vessel Technology 115, nr 2 (1.05.1993): 185–92. http://dx.doi.org/10.1115/1.2929514.

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Towards assessing the creep-fatigue damage for the inner vessel of a pool-type fast reactor, 3-D elastic and axisymmetric inelastic analysis with classical kinematic hardening model, ORNL material model and more realistic CHABOCHE visco-plastic model have been performed. The material properties of stainless steel type 316 LN at various temperatures are used in the analysis. Using the results of this analysis, the creep-fatigue damage and ratcheting are assessed as per the rules of RCC-MR and results have been compared for the various constitutive models used. Inelastic analysis has been performed only at highly stressed local regions. Computations with the ORNL material model is found to be satisfactory in terms of conservatism and computer cost involved, and hence recommended for use in the design stage. Further, conservatism in estimating the creep fatigue-damage of the component associated with the elastic route of RCC-MR has been quantified. The inelastic and viscoplastic analysis tool has been validated using experimental benchmark problems.

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Li, Ming, Hai Pu i Lili Cao. "Variable-order fractional creep model of mudstone under high-temperature". Thermal Science 21, suppl. 1 (2017): 343–49. http://dx.doi.org/10.2298/tsci17s1343l.

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In order to study the properties of high-temperature creep for mudstone, MTS810 electro-hydraulic servo material test system and MTS652.02 high temperature furnace are utilized for the creep test of mudstone at 700?C. Considering the visco-elastic-plastic characteristics and the damage effect, the variable-order fractional creep model is established to research the creep character, and it is found that the proposed model can be well fitting of our experimental results. Especially, variable-order function can be used to analyze and study the viscoelastic property evolution of mudstone in process of high-temperature creep. Compositions of mudstone are distinguished by X-ray diffraction technology. The presence of the illite under high temperatures can be used for explaining the viscous feature prevails over the elastic ones in viscoelastic properties.

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Zhang, Jie, Abel Cherouat i Houman Borouchaki. "3D Thermo-Mechanical Simulation Coupled with Adaptive Remeshing for Metal Milling". Advanced Materials Research 698 (maj 2013): 11–20. http://dx.doi.org/10.4028/www.scientific.net/amr.698.11.

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As a material removal process, metal milling process involves large geometry deformation, material thermo-visco-plastic flow coupled with damage and complex contact-friction problems. During simulation of metal milling, the finite elements distort severely at the local regions with high gradient of physical field such as stress, strain and temperature due to these problems. This paper presents numerical adaptive remeshing procedure dedicated to metal milling process. The procedure integrates Explicit solver of ABAQUS, OPTIFORM mesher and python script program transfer to execute step by step the incremental milling process. At each step, the meshes are refined and coarsened automatically based on geometrical and physical error estimations; the physical fields are transferred (point to point) from old to the new one using advanced algorithm. Johnson-cook material model is used to simulate the material plastic flow with ductile damage. Some numerical results are given to demonstrate the efficiency of the proposed procedure.

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Bian, Hanbing, Xiaotian Zhang i Jianfu Shao. "A coupled elastoplastic and visco-plastic damage model for hard clay and its application for the underground gallery excavation". Underground Space 2, nr 1 (marzec 2017): 60–72. http://dx.doi.org/10.1016/j.undsp.2017.03.002.

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CHEN, HONGJIE, WEIYA XU, WEI WANG, RUBIN WANG i CHONG SHI. "A NONLINEAR VISCOELASTIC-PLASTIC RHEOLOGICAL MODEL FOR ROCKS BASED ON FRACTIONAL DERIVATIVE THEORY". International Journal of Modern Physics B 27, nr 25 (12.09.2013): 1350149. http://dx.doi.org/10.1142/s021797921350149x.

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The soft-matter element between the ideal solid and the ideal liquid is established and is described based on the definition of the fractional derivatives. By replacing a component in the generalized Kelvin model with the soft-matter component and connecting it in series with a nonlinear visco-plastic body, a nonlinear viscoelasto-plastic rheological model is proposed based on the fractional derivatives in order to describe the rheological behaviors of rocks. The data obtained from the triaxial creep tests of a typical rock are simulated with this model and the fitting result is good. The model can describe well three rheological stages of the rock during the triaxial creep tests. The validity of this model is then discussed. In this model, the fractional order β controls creep strain rate in the stable creep stage under the condition of low stress; while the creep index n controls creep rate of the accelerated rheological stage under the condition of high stress. Few parameters and good simulation results manifest the outstanding performance of the model. The model also adopts the damage theory to describe the progressive deterioration of rock viscous coefficient of the accelerated creep stage. The model can also give an excellent description of the three rheological stages of rocks, especially the accelerated creep stage.

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Lis, Adrian, Koji Asama, Tomoki Matsuda, Tomokazu Sano i Akio Hirose. "Strength assessment for direct-sintered Al2O3-to-Cu joints based on damage modeling". International Symposium on Microelectronics 2017, nr 1 (1.10.2017): 000613–18. http://dx.doi.org/10.4071/isom-2017-tha51_123.

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Abstract Metal-to-ceramics direct sintering was carried out with Al2O3 and Cu / 3 μm Ni / 1 μm Au substrates. The bonding paste consisted of micron-sized Ag2O particles and a reducing solvent that provokes Ag2O-to-Ag reduction during processing accompanied by the formation of Ag nano particles. Five different sets of process parameters resulted in different joint microstructure and strength. The experimental data was used to calibrate an elasto-visco-plastic finite element model of the sintered assembly which yielded a quantitative damage function and criterion to predict the strength of direct-sintered joints. The developed ductile damage formulation introduced a parameter ξ, i.e. the product of equivalent creep strain and stress triaxiality, that controls the tolerable plastic strain at fracture. An extended numerical parameter study subsequently revealed the complex interaction between the joint strength and microstructural joint features. Thinner joints were found to provide a slightly higher strength while the amount of sinter material and costs is significantly reduced. Moreover, it is recommended to aim at a higher level of densification at the edges and corners of sintered joints since these areas apparently contribute more to the overall mechanical strength. The developed concept is capable of tailoring the microstructure of direct-sintered joints according to the requirements or vice versa.

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Zheng, Kai Lun, Lei Zhu, Denis J. Politis, Jian Guo Lin i Trevor A. Dean. "An Analytical and Numerical Investigation on Flange Wrinkling Behavior in Warm Forming Process of AA5754 Using Macro-Textured Tool Design". Key Engineering Materials 716 (październik 2016): 586–94. http://dx.doi.org/10.4028/www.scientific.net/kem.716.586.

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In this paper, an analytical buckling model is established to predict the flange wrinkling behavior of deep drawn cylindrical cups of aluminium alloy sheet in warm forming conditions using macro-textured blankholders for the first time. A continuum damage mechanism (CDM) based material model was utilized to reflect the visco-plastic feature of material at elevated temperatures. Forming speed and temperature effects were investigated, and texture ratio and draw ratio effects were also discussed. The developed analytical buckling model was validated by finite element simulations. The increase of forming temperature and forming speed is prone to cause wrinkling for AA5754, but the effects are not as significant as the texture geometry and draw ratio. The analytical model presented in this paper can be used as a design guide to determine tool texture geometry necessary to avoid wrinkling defects in the warm forming processes of aluminium alloy.

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Zohravi, Sara Ebrahimi, Ali Lakirouhani, Hamed Molladavoodi, Jurgis Medzvieckas i Romualdas Kliukas. "A NEW CONSTITUTIVE MODEL FOR THE TIME-DEPENDENT BEHAVIOR OF ROCKS WITH CONSIDERATION OF DAMAGE PARAMETER". JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 28, nr 3 (2.03.2022): 223–31. http://dx.doi.org/10.3846/jcem.2022.16609.

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Deformation and time-dependent behavior of rocks are closely related to the stability and safety of underground structures and mines. In this paper, a numerical-analytical model is presented to investigate time-dependent damage and deformation of rocks under creep. The proposed model is obtained by combining the elastic-visco-plastic model based on the theory of over-stress and stress hardening law with the sub-critical crack growth model. The advantage of this model is that it is in incremental form and therefore can be implemented numerically. First, the governing equations of the model and its numerical computational algorithm are described. The proposed constitutive model is then implemented in the FLAC code using the FISH function. Determination of model parameters and calibration is done by various laboratory tests performed on a type of gypsum. The creep test was performed on gypsum under a stress of 13 MPa, which is equal to 70% of its compressive strength. After determining the parameters, by fitting the creep curve of the presented analyticalnumerical model, a good agreement is observed with the creep curve obtained from the laboratory data. It is also observed that during creep, the damage parameter and wing crack length increase.

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Zhang, Jie, Abel Cherouat i Houman Borouchaki. "FE Simulation of Metal Orthogonal Cutting Processes Based on 3D Adaptive Remeshing Procedure". Advanced Materials Research 409 (listopad 2011): 461–66. http://dx.doi.org/10.4028/www.scientific.net/amr.409.461.

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Metal orthogonal cutting process involves complex geometry deformation and mate-rial characteristics as large thermal-visco-plastic ow include ductile damage. Simultaneously,the contact with friction occurs in the same zone. To build the nite element model for metalcutting, the nite element mesh will be severely distorted at the region with high gradientof stress/strain/temperature eld. In this paper, a Adaptive remeshing procedure which inte-grates the 3D OPTIFORM mesher, ABAQUS/Explicit solver and eld node-node eld transferalgorithm are proposed to solve these problems. The thermal-mechanical simulation for metalorthogonal cutting is realized to demonstrate our numerical simulation approach. Some simu-lation results are illustrated include continuous chip forming process, thermal-mechanical elddistribution and cutting force in di erent rank angles, cutting speeds and friction conditions.

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Zhao, X. J., G. Q. Zhang, J. F. J. M. Caers i L. J. Ernst. "Solders Fatigue Prediction Using Interfacial Boundary Volume Criterion". Journal of Electronic Packaging 125, nr 4 (1.12.2003): 582–88. http://dx.doi.org/10.1115/1.1604160.

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In this paper, an “interfacial boundary volume” based damage criterion was proposed in combination with the modified Coffin-Manson model to predict solder fatigue. This criterion assumes that mainly, the behavior of the thin solder layer at chip pad interface contributes to the solder fatigue, not the whole solder joint or the averaged strains from randomly selected elements. The damage parameter was thus calculated by averaging the visco-plastic strain range over the interfacial boundary layer volume in the solder and later related to the corresponding fatigue life of experimental test through least-squares curves fitting to determine the empirical coefficients in the Coffin-Manson equation. As a demonstrator, the solder joint fatigue in wafer level chip scale packaging under thermal shock loading was analyzed. An appropriate constitutive relation from Darveaux was used to model the inelastic deformation of the solder alloy, and the different stress-strain responses resulting from different designs were calculated. The analysis results were used to develop the empirical fatigue model based on the interfacial boundary volume damage criterion and then this fatigue model was used for prediction. The fatigue lives of chip scale packaging with variable solder land size and component size were analyzed using this model. The prediction results match well with those from experimental tests. For this demonstrator, it was also shown that the empirical model based on the interfacial boundary volume criterion was more accurate than the models obtained from other strain averaging methods.

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Zhang, Chunyang, Ping Zou, Yixian Wang, Tingting Jiang, Hang Lin i Ping Cao. "An elasto-visco-plastic model based on stress functions for deformation and damage of water-saturated rocks during the freeze-thaw process". Construction and Building Materials 250 (lipiec 2020): 118862. http://dx.doi.org/10.1016/j.conbuildmat.2020.118862.

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Tamin, M. N., i H. Ghonem. "Fatigue Damage Mechanisms of Bridging Fibers in Titanium Metal Matrix Composites1". Journal of Engineering Materials and Technology 122, nr 4 (4.05.2000): 370–75. http://dx.doi.org/10.1115/1.1288770.

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This paper investigates the fatigue damage mechanisms of SiC fibers bridging a fatigue crack in unidirectional reinforced titanium matrix composites. For this purpose, an experimental/computational fiber fracture model is developed on the basis of the occurrence of two damage events taking place along a bridging fiber. These events are the time-dependent evolution of axial stresses and the simultaneous strength degradation of the fiber due to cyclic-related damage processes. The stress evolution in a fiber is calculated using the finite element method employing a cylinder model of a fiber embedded in a cracked matrix phase. The model considers the visco-plastic behavior of the matrix phase at elevated temperature loadings. The failure strength of the as-received SiC fiber are determined through a series of monotonic tension, residual fatigue strength and fatigue-life tests performed on SiC fibers at different temperatures. In order to take into account the notch-like effects resulting from the presence of fiber coating cracks and possible deflection of fiber/matrix interfacial cracks, the fatigue strength of the as-received SiC fiber was modified using elastic stress localization. The resulting fatigue strength of bridging fibers was found to be about 56 percent less than the corresponding strength of as-received fibers. The fiber stress evolution curve and the modified fatigue strength curve were then combined to predict the life of bridging fibers. Results of the model are compared with those obtained experimentally for bridging fibers in SiC/Timetal-21S composite subjected to load conditions including low and high loading frequency at 500 and 650°C. [S0094-4289(00)01804-1]

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Rajhi, W. "Numerical Simulation of Damage on Warm Deep Drawing of Al 6061-T6 Aluminium Alloy". Engineering, Technology & Applied Science Research 9, nr 5 (9.10.2019): 4830–34. http://dx.doi.org/10.48084/etasr.3148.

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This work focuses on the numerical simulation of warm deep drawing operation of car sump oil made with Al 6061-T6 aluminum alloy for the purpose of process optimization. The thermo visco-plastic behavior with damage effect of the material is described by the Johnson-Cook (JC) model. The JC model parameters for the Al 6061-T6 Aluminum alloy were exploited. Numerical simulation of the deep drawing operation was performed with the use of the ABAQUS FE software thanks to the dynamic Explicit Temperature-Displacement algorithm. The design of the different tools is obtained on the basis of the geometry of the finished product. Designing of punch, die and blank holder is performed using CATIA 3D CAD software. The warm forming method involves the heating of the blank holder and the die to a certain temperature, whereas, the punch is kept at room temperature. In this study, predefined temperatures of the die and blank holder and punch speed will be investigated among other stamping parameters. The computed damage evolution curves for a given set of the process parameters are retrieved at the end of the simulation to determine suitable forming conditions. It can be noted that the slower the damage evolution achieved within the blank, the more appropriate the process parameters. Thus, by increasing strain rate, main cracks change location.

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Torres, Dery, Shu Guo, Maria-Pilar Villar, Daniel Araujo i Rafael Estevez. "Calibration of a Cohesive Model for Fracture in Low Cross-Linked Epoxy Resins". Polymers 10, nr 12 (28.11.2018): 1321. http://dx.doi.org/10.3390/polym10121321.

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Polymer-based composites are becoming widely used for structural applications, in particular in the aeronautic industry. The present investigation focuses on the mechanical integrity of an epoxy resin of which possible damage results in limitation or early stages of dramatic failure. Therefore, a coupled experimental and numerical investigation of failure in an epoxy resin thermoset is carried out that opens the route to an overall micromechanical analysis of thermoset-based composites. In the present case, failure is preceded by noticeable plasticity in the form of shear bands similar to observations in ductile glassy polymers. Thus, an elastic-visco-plastic constitutive law initially devoted to glassy polymer is adopted that captures the rate- dependent yield stress followed by softening and progressive hardening at continued deformation. A general rate-dependent cohesive model is used to describe the failure process. The parameters involved in the description are carefully identified and used in a finite element calculation to predict the material’s toughness for different configurations. Furthermore, the present work allows investigation of nucleation and crack growth in such resins. In particular, a minimum toughness can be derived from the model which is difficult to evaluate experimentally and allows accounting for the notch effect on the onset of failure. This is thought to help in designing polymer-based composites.

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Signoret, Charles, Anne-Sophie Caro-Bretelle, José-Marie Lopez-Cuesta, Patrick Ienny i Didier Perrin. "Impact of PP Impurities on ABS Tensile Properties: Computational Mechanical Modelling Aspects". Polymers 13, nr 10 (19.05.2021): 1647. http://dx.doi.org/10.3390/polym13101647.

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Recycling of plastics is hindered by their important variety and strong incompatibility. However, sorting technologies bear costs and meet limits. Very high purities (<2 wt%) are difficult to reach. Yet, such rates may be detrimental to functional properties. In this work, an ABS matrix (major plastic in Waste of Electrical and Electronic Equipments) was filled with 4 wt% of PP to mimic impurities in ABS after recycling. PP-g-MA was introduced in the blend to improve the compatibility. A finite element model was developed from the mechanical behavior of each component. ABS and PP were individually characterized from tensile tests instrumented with photomechanics and their behaviors were modelled through a set of numerical parameters (elasto-visco-plasticity with a Gurson’s criterion behavior). Comparison between the determinist model results and the experimental data (strength, volumetric variation) shows that this type of modelling could be a predictive tool in order to anticipate composite mechanical properties and to understand micromechanisms of deformation (damage, cavitation). The main result is that PP introduced at 4 wt% into ABS does not alter the static mechanical properties despite polymers incompatibility. The addition of PP-g-MA modifies the local properties and possibly conduct to a premature breakage of the polymer blend.

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Puzrin, Alexander M., i Andreas Schmid. "Progressive failure of a constrained creeping landslide". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, nr 2133 (30.03.2011): 2444–61. http://dx.doi.org/10.1098/rspa.2011.0063.

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The ski resort town of St Moritz, Switzerland, is partially constructed on a large creeping landslide, which has been causing damage to buildings and infrastructure. At the town centre, the landslide is constrained by a rock outcrop, creating a compression zone in the sliding mass. After decades of gradual slowing down,s in the beginning of 1990s the landslide started to accelerate, in spite of the fact that the average yearly precipitation and the pore water pressure on the sliding surface remained fairly constant. The paper shows that a constrained creeping landslide experiences progressive failure caused by the propagation of a zone of intense shearing along the slip surface resulting in significant earth pressure increase and visco-plastic yielding of soil in the compression zone. This basic physical mechanism, relying on extensive laboratory and field tests and long-term displacement monitoring, explains the paradox of the St Moritz landslide acceleration. Although the model predicts that the landslide could eventually slow down, its displacements may become excessive for some buildings, requiring an early warning system and further stabilization of the historic Leaning Tower. In general, by predicting the onset of yielding, the model can provide an important timeframe for stabilization of constrained landslides.

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Wang, Xingkai, Wansheng Wei, Yong Niu, Caichu Xia, Leibo Song, Guansheng Han i Zheming Zhu. "Triaxial Creep Mechanical Behaviors and Creep Damage Model of Dolomitic Limestone Material under Multi-Stage Incremental Loading". Materials 16, nr 5 (25.02.2023): 1918. http://dx.doi.org/10.3390/ma16051918.

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Dolomitic limestone is the main surrounding rock material in Yangzong tunnel engineering; the instantaneous mechanical properties and creep behaviors of limestone are significant for stability evaluation during the stages of tunnel excavation and long-term maintenance. Herein, four conventional triaxial compression tests were carried out to explore its instantaneous mechanical behavior and failure characteristics; subsequently, the creep behaviors of limestone subjected to multi-stage incremental axial loading at the confinements of 9 MPa and 15 MPa were studied by employing an advanced rock mechanics testing system (i.e., MTS815.04). The results reveal the following. (1) comparing the curves of axial strain–, radial strain–, and volumetric strain–stress under different confining pressures shows that these curves present a similar trend, whereas the stress drops during the post-peak stage decelerate with the increase in confining pressure, suggesting that the rock transits from brittleness to ductility. The confining pressure also has a certain role in controlling the cracking deformation during the pre-peak stage. Besides, the proportions of compaction- and dilatancy-dominated phases in the volumetric strain–stress curves differ obviously. Moreover, the failure mode of the dolomitic limestone is a shear-dominated fracture but is also affected by the confining pressure. (2) When the loading stress reaches a creep threshold stress, the primary and steady-state creep stages occur successively, and a higher deviatoric stress corresponds to a greater creep strain. When the deviatoric stress surpasses an accelerated creep threshold stress, a tertiary creep appears and then is followed by creep failure. Furthermore, the two threshold stresses at 15 MPa confinement are greater than that at 9 MPa confinement, suggesting that the confining pressure has an obvious impact on the threshold values and a higher confining pressure corresponds to a greater threshold value. Additionally, the specimen’s creep failure mode is one of “abrupt” shear-dominated fracturing and is similar to that under a conventional triaxial compression test at high confining pressure. (3) A multi-element nonlinear creep damage model is developed by bonding a proposed visco-plastic model in series with the Hookean substance and Schiffman body, and can accurately describe the full-stage creep behaviors.

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Ranjith Kumar, G., i G. Rajyalakshmi. "Taguchi Grey Relational Approach for Optimizing Process Parameters of Laser Peening on Titanium Alloy to Induce Enhanced Compressive Stress based on Finite Element Simulation". Journal of Advanced Manufacturing Systems 19, nr 02 (czerwiec 2020): 365–87. http://dx.doi.org/10.1142/s0219686720500183.

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Laser Shock Peening (LSP) turned out to be the most efficient surface engineering process for advanced materials to induce beneficial deep compressive residual stress which helps in improving mechanical, fatigue properties and surface damage resistance. But, analyzing the nonuniform distribution of residual stresses in the treated sample with X-ray diffraction (XRD) is much time taking and a costly process. This problem can be resolved with LSP finite element numerical simulation model which is feasible with the realistic experimental process. The FE model allows the user to control the laser parameters in order to achieve the optimal level of all controllable parameters. This study is intended to analyze and optimize the influence of laser processing parameters that assists in inducing the residual compressive stress with minimal surface deformation. A Ti6Al4V material model with Johnson–Cook’s visco-elastic–plastic material behavior law is prepared for LSP simulation. Gaussian pressure profile is utilized for uniform loading of the targeted zone for the proposed model. Taguchi Grey Relational Analysis (TGRA) with L27 orthogonal array is applied to LSP simulation, and the results were analyzed with consideration of multiple response measures. It is noted that surface deformation is increased with the rise in a number of laser shots and pressure pulse duration. Maximum compressive residual stresses are falling for higher levels of laser spot diameter, laser spot overlap and laser power density. The correlation is observed between the FE simulation and the published results. The optimal set of process parameters are obtained for improving the LSP on Ti alloys.

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Allen, Robert, Laszlo Toth, Andrew Oppedal i Haitham El Kadiri. "Crystal Plasticity Modeling of Anisotropic Hardening and Texture Due to Dislocation Transmutation in Twinning". Materials 11, nr 10 (28.09.2018): 1855. http://dx.doi.org/10.3390/ma11101855.

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In crystalline materials, dislocations are three-dimensional lattice distortions that systematically distort twin interfaces that they encounter. This results in dislocation dissociation events and changes in the atomic structure of the interface. The manner in which the interface distorts drive the product of the dissociation event, and consequently, the incident dislocation core and the magnitude and relative direction of the Burgers vector govern these slip-twin interaction phenomena. Recent characterization studies using transmission electron microscopy as well as advanced molecular dynamic simulations have shown that slip dislocations, whether striking or struck by a {10 1 ¯ 2} twin boundary, dissociate into a combination of twinning disconnections, interfacial disclinations (facets), jogs, and other types of dislocations engulfed inside the twin domains, called transmuted dislocations. While twinning disconnections were found to promote twin propagation, the dislocations incorporated inside the twin are of considerable importance to hardening and damage initiation as they more significantly obstruct slip dislocations accommodating plasticity of the twins. In this work, the dislocation transmutation event and its effect on hardening is captured using a dislocation density based hardening model contained in a visco-plastic self-consistent mean-field model. This is done by allowing the twins to increase their dislocation densities, not only by virtue of slip inside the twin, but also through dislocations that transmute from the parents as the twin volume fraction increases. A correspondence matrix rule is used to determine the type of converted dislocations while tracking and parameterizing their evolution. This hypothesis provides a modeling framework for capturing slip-twin interactions. The model is used to simulate the mechanical response of pure Mg and provides a more physically based approach for modeling stress-strain behavior.

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Preuss, Simon, Jean Paul Ampuero, Taras Gerya i Ylona van Dinther. "Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults". Solid Earth 11, nr 4 (22.07.2020): 1333–60. http://dx.doi.org/10.5194/se-11-1333-2020.

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Abstract. Natural fault networks are geometrically complex systems that evolve through time. The evolution of faults and their off-fault damage patterns are influenced by both dynamic earthquake ruptures and aseismic deformation in the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate- and state-dependent friction. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation is created to incorporate the effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localization is facilitated by plastic strain weakening of bulk rate and state friction parameters as inspired by laboratory experiments. This allows us to simulate sequences of episodic fault growth due to earthquakes and aseismic creep for the first time. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity weakening to velocity strengthening. Interestingly, in each of these bulk rheologies, faults predominantly localize and grow due to aseismic deformation. Yet, cyclic fault growth at more realistic growth rates is obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Fault growth occurs under Riedel and conjugate angles and transitions towards wing cracks. Off-fault deformation, both distributed and localized, is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized splay faults. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighboring fault strands affect primary and secondary fault growth and thus that normal stress variations affect earthquake sequences. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend, individual fault strands interact, and optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics.

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Chen, Bao, Xuan Cang Wang i Ke Mu. "Mechanical Response of Longitudinal Slope Segments Based on Burgers Model". Advanced Materials Research 243-249 (maj 2011): 4172–77. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.4172.

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Asphalt Pavement was damaged more seriously in longitudinal Gradient than common segment because of its special load bearing conditions. This paper establishes a 3D Visco-elasto-plastic Finite Element to analyses the stress respond of pavement structure, calculating the discipline of stress behaviors under different gradient. Burgers model was used to study the factors which can influence on tracking, for example longitudinal Gradient, speeds and frequency of axle load. Result of calculation show that the maximum shear stress grows as the gradient increases. Rutting of pavement was small before a certain number of axle loads, but when beyond the certain number, the rutting incense notably, and the slower speed the vehicle has, the deeper tracking the pavement responds.

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Konrad, Julian, Sebastian Pfaller i Dirk Zahn. "Multi-Scale Modelling of Plastic Deformation, Damage and Relaxation in Epoxy Resins". Polymers 14, nr 16 (9.08.2022): 3240. http://dx.doi.org/10.3390/polym14163240.

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Epoxy resin plasticity and damage was studied from molecular dynamic simulations and interpreted by the help of constitutive modelling. For the latter, we suggested a physically motivated approach that aims at interpolating two well-defined limiting cases; namely, pulling at the vanishing strain rate and very rapid deformation; here, taken as 50% of the speed of sound of the material. In turn, to consider 0.1–10-m/s-scale deformation rates, we employed a simple relaxation model featuring exponential stress decay with a relaxation time of 1.5 ns. As benchmarks, deformation and strain reversal runs were performed by molecular dynamic simulations using two different strain rates. Our analyses show the importance of molecular rearrangements within the epoxy network loops for rationalizing the strain-rate dependence of plasticity and residual stress upon strain reversal. To this end, our constitutive model reasonably reproduced experimental data of elastic and visco-elastic epoxy deformation, along with the maximum stress experienced before fracturing. Moreover, we show the importance of introducing damage elements for mimicking the mechanical behavior of epoxy resins.

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Zhao, Baoyun, Yingjie Wu, Jiaosheng Yang, Juncang Sun, Wei Huang, Ziyun Li i Shuhan Zhang. "Mechanical Properties of Gas Storage Sandstone under Uniaxial Cyclic Loading and Unloading Condition". Periodica Polytechnica Civil Engineering, 6.03.2023. http://dx.doi.org/10.3311/ppci.21620.

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In order to study the mechanical properties and damage evolution of the gas storage surrounding rock under the periodic injection-production process, the uniaxial cyclic loading and unloading tests of sandstone were carried out by TFD-2000 microcomputer servo-controlled rock triaxial testing machine. Results shown that the compressive strength of gas storage sandstone specimens were gradually decreases with increasing of the stress amplitude after 200 cycles. The stress-strain curve under uniaxial cyclic loading and unloading condition formed hysteresis loops, and the hysteresis loop presented sparse-dense-sparse when the stress amplitude was relative higher. The residual strains can be divided into three stages of decay deformation stage, stable deformation stage and accelerated deformation stage when the stress amplitude is 8~32 MPa, this phenomenon is very similar to the creep behavior of rocks. The energy evolution of sandstone under cyclic loading and unloading was analyzed and the damage evolution low of which was also discussed in detail, the damage variable defined by energy dissipative ratio accumulation can well reflect the damage development of sandstone under uniaxial cyclic loading and unloading. A nonlinear visco-plastic body was proposed by considering the accelerate stage of curves of the axial residual strains, and used the nonlinear visco-plastic body to replace the visco-plastic body of the traditional Nishihara model, a nonlinear viscoelastic-plastic model for cyclic loads was established and the applicability of the model is verified. The research results provide certain reference value for the construction and maintenance of gas storage.

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Xu, Guowen, Marte Gutierrez, Ketan Arora i Xin Wang. "Visco-plastic response of deep tunnels based on a fractional damage creep constitutive model". Acta Geotechnica, 29.05.2021. http://dx.doi.org/10.1007/s11440-021-01226-5.

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Zhang, Xing, Hang Lin, Huihua Hu, Yanhui Cheng i Wanyi Zhang. "A nonlinear rheological shear constitutive model of bolted joints considering initial damage and damage evolution". International Journal of Damage Mechanics, 29.06.2023. http://dx.doi.org/10.1177/10567895231183468.

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Understanding the shear mechanics mechanism of bolted joints is of great significance for predicting and preventing geological disasters. Most current studies seldom consider the rheological effects of bolted joints. In this paper, a comprehensive rheological constitutive model is proposed, accounting for initial damage and damage evolution across different rheological stages and bolt characteristics. The model incorporates an elastoplastic Hooke body for instantaneous deformation, parametric nonlinear Kelvin and viscous models for attenuation and steady creep stages, and a visco-plastic model based on time-dependent shear strength for accelerated creep stage. Additionally, a bolt-rock cooperative deformation model is introduced, considering the evolution of the bolt's elastic modulus. The resulting elasto-viscoplastic constitutive model effectively describes the shear rheological behavior of bolted joints, with its validity and superiority demonstrated through comparisons with shear creep tests and the Maxwell model. This research aims to provide valuable theoretical guidance for the construction and reinforcement of rock mass engineering projects.

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Huo, Yuanming, Wanbo Yang, Tao He, Jie Bai, Jianye Gao i Cunlong Huo. "A Novel Unified Visco-Plastic Damage Constitutive Model Considering Stress State of TC16 Titanium Alloy during Cold Deformation". Journal of Materials Engineering and Performance, 3.10.2022. http://dx.doi.org/10.1007/s11665-022-07415-x.

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"Numerical Modeling the Effects of Chamfer and Hone Cutting Edge Geometries on Burr Formation". WSEAS TRANSACTIONS ON APPLIED AND THEORETICAL MECHANICS 15 (7.12.2020). http://dx.doi.org/10.37394/232011.2020.15.17.

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A finite element based numerical model to simulate orthogonal machining process and associated burr formation process has been developed in the presented work. To incorporate simultaneous effects of mechanical and thermal loadings in high speed machining processes, Johnson and Cook`s thermo-visco-plastic flow stress model has been adopted in the conceived numerical model. A coupled damage-fracture energy approach has been used to observe damage evolution in workpiece and to serve as chip separation criterion. Simulation results concerning chip morphology, nodal temperatures, cutting forces and end (exit) burr have been recorded. Model has been validated by comparing chip morphology and cutting force results with experimental findings in the published literature. Effects of cutting edge geometries [Hone and Chamfer (T-land)] on burr formation have been investigated thoroughly and discussed in length. To propose optimum tool edge geometries for reduced burr formation in machining of an aerospace grade aluminum alloy AA2024, numerical analyses considering multiple combinations of cutting speed (two variations), feed (two variations) and tool edge geometries [Hone edge (two variations), Chamfer edge (four variations)] have been performed. For chamfer cutting edge, the “chamfer length” has been identified as the most influential macro geometrical parameter in enhancing the burr formation. Conversely, “chamfer angle” variation has been found least effecting the burr generation phenomenon.

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Yamaguchi, Yuya, Fumiyasu Makinoshima i Yusuke Oishi. "Simulating the entire rainfall-induced landslide process using the material point method for unsaturated soil with implicit and explicit formulations". Landslides, 2.05.2023. http://dx.doi.org/10.1007/s10346-023-02052-4.

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AbstractRainfall-induced landslides cause various types of damage, including damage to infrastructure, leading to devastating economic losses and human casualties. Although various numerical methods have been developed to predict landslide occurrence and the extent of sediment flow, three-dimensional analysis of the entire landslide process in a unified manner is still challenging owing to limitations in computational efficiency and the representation of deformation and flow. In this study, we present a numerical method of rainfall-induced landslides using the coupled hydromechanical material point method (MPM) for unsaturated porous media based on implicit and explicit formulations, which enables the efficient analysis of all rainfall-induced landslide processes, including both quasi-static and dynamic processes. The developed method includes an implicit MPM based on a simplified formulation, which is first applied to the quasi-static analysis in the pre-failure stages in which rainwater infiltrates the ground. The explicit MPM is then applied to the dynamic analysis for post-failure stages in which the ground collapses and flows. A constitutive law for soils is improved in the simulation of landslide initiation and sediment flow by incorporating the effect of cohesion in a visco-plastic model for granular materials. The proposed method was applied to a three-dimensional terrain model of Ashikita town, Kumamoto, Japan, where an actual landslide occurred owing to intense rainfall on July 3–4, 2020. Numerical results from the proposed hydromechanical coupling compared with single-phase MPM indicated that pore water plays an important role in understanding all rainfall-induced landslide processes, from landslide initiation to sediment discharge.

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Yao, Yao, Xu Long i Leon M. Keer. "A Review of Recent Research on the Mechanical Behavior of Lead-Free Solders". Applied Mechanics Reviews 69, nr 4 (1.07.2017). http://dx.doi.org/10.1115/1.4037462.

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Due to the restriction of lead-rich solder and the miniaturization of electronic packaging devices, lead-free solders have replaced lead-rich solders in the past decades; however, it also brings new technical problems. Reliability, fatigue, and drop resistance are of concern in the electronic industry. The paper provides a comprehensive survey of recent research on the methodologies to describe the mechanical behavior of lead-free solders. In order to understand the fundamental mechanical behavior of lead-free solders, the visco-plastic characteristics should be considered in the constitutive modeling. Under mechanical and thermal cycling, fatigue is related to the time to failure and can be predicted based on the analysis to strain, hysteresis energy, and damage accumulation. For electronic devices with potential drop impacts, drop resistance plays an essential role to assess the mechanical reliability of solder joints through experimental studies, establishing the rate-dependent material properties and proposing advanced numerical techniques to model the interconnect failure. The failure mechanisms of solder joints are complicated under coupled electrical-thermal-mechanical loadings, the increased current density can lead to electromigration around the current crowding zone. The induced void initiation and propagation have been investigated based on theoretical approaches to reveal the effects on the mechanical properties of solder joints. To elucidate the dominant mechanisms, the effects of current stressing and elevated temperature on mechanical behavior of lead-free solder have been reviewed. Potential directions for future research have been discussed.

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"Nuclear Containment Wall under Aircraft Crash". International Journal of Recent Technology and Engineering 8, nr 3 (30.09.2019): 3249–56. http://dx.doi.org/10.35940/ijrte.c5408.098319.

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The safety analysis of important structure such as nuclear power plant against commercial aircraft has been studied. In the present study, a stepwise sequential analysis has been performed to determine the stresses on the nuclear containment wall under aircraft crash and induced fire effects. ABAQUS/Implicit finite element code was followed to get the response of the nuclear containment. First, the impact load is applied on the containment using Riera force history curve of Boeing 707-320, after 0.16 sec nodal temperatures were increased following the proposed jet fuel curve to imitate fire as a result of fuel burning. Combined effect of impact and heat has been used to study thermal stress variation. As the fuel is stored in the wings of the plane, the effect of fire is assumed to trigger as soon as the wings hit the outer face of containment wall. From Riera force history curve, time delay between plane’s first contact and wing contact with the containment wall was assumed to be 0.16 second. The effect due to fire was considered to be most severe at 10 m height from the base of containment structure. This is due to the fact that post-impact most of the fuel will immediately flow down to the bottom of containment. In the impact region, moderate fire for 15 minutes has been considered. The fire duration has been considered for 2 hrs at severe zone. The deformed geometry of model in impact analysis is then assumed to be the initial state for the thermal stress analysis. The concrete damaged plasticity model for concrete and JohnsonCook elastic-visco plastic material model for reinforcement have been taken to predict the behavior of concrete and steel. For heat transfer and thermal stress analysis, the material properties have been taken at elevated temperature form Eurocode 2. The containment has a circular cylindrical wall of inner diameter 42 m and thickness 0.85m excluding 6mm steel plate which was provided at the inner face of containment. The total height of the containment was assumed to be 60 m. The impact location of the aircraft was considered at the mid-height of the containment as more deformation was observed in this location

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