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The study of damage and failure in fractured rock masses is crucial. This study employs the representative volume element (RVE) method to develop a microscale rock model. The model simulates the propagation and rupture of fractures by integrating factors including actual mineralogical composition, the Weibull distribution function, the Mohr–Coulomb damage criterion, and strain softening. Results indicate that fractures reduce the uniaxial compressive strength of the rock and that peak strength is significantly correlated with crack geometries. Plastic damage in rocks was categorized into three stages: elastic, rapid growth, and postpeak softening. A logistic growth model describes the plastic volume change curves for rocks with various fracture geometries, establishing the relationship between plastic damage volume and damage variables. Constitutive models for rocks with varying fracture geometries under uniaxial compression were formulated. The accuracy and applicability of these models were validated, providing a theoretical basis for rock engineering applications. Highlights: A heterogeneous plastic damage model based on representative volume elements is developed.A logistic growth model was used to describe the plastic volume change curves for rocks containing different fracture geometries.The relationship between rock plastic damage volume and damage variables was established.Plastic damage constitutive models of rocks containing different fracture geometries under uniaxial compression were obtained and validated. [ABSTRACT FROM AUTHOR]

ABSTRACT To safely and effectively explore the natural methane hydrate, it is crucial to examine the mechanical behavior of methane hydrate‐bearing sediments (MHBSs). Natural methane hydrate unevenly distributes in pores or bonds with soil particles in MHBS, changing the mechanical behavior of MHBS including stiffness, shear strength, and dilatancy. This paper presents an anisotropic critical state model for MHBS considering hydrate pore‐filling and cementing effects. Based on the unified critical state model for both clay and sand, an equivalent hydrate ratio is defined to address pore‐filling effect. Cohesive strength and its hardening law are introduced to characterize hydrate cementation. To describe the anisotropic behavior, the inherent anisotropy of soil particles and hydrates are modeled separately, and rotation hardening is introduced to describe the stress‐induced anisotropy. Comparisons with existing triaxial tests of both synthetic and natural MHBS demonstrate that the proposed model comprehensively describes the mechanical behavior of MHBS. Detailed predictions indicate that hydrate pore‐filling affects the hydrate‐dependent stiffness and dilatancy of MHBS, which become more pronounced with increasing hydrate saturation. Cementing effect increases the initial stiffness and peak strength of MHBS. The pronounced influence of inherent anisotropic parameters on pre‐peak stress–strain relation of MHBS is noted, and increasing hydrate saturation enhances the effect of hydrate anisotropy. These predictions contribute to a better understanding of the relation between hydrate morphologies and MHBS mechanical properties. [ABSTRACT FROM AUTHOR]

This study introduces a one‐dimensional phenomenological constitutive model designed to describe two‐way shape memory effect (TWSME) and its associated cyclic degradation. The model utilizes the logistic function to formulate the phase transformation equation, incorporates the expansion of key parameters into their respective fatigue functions to characterize the fatigue phenomenon, and integrates a phase transformation rate regulation function into the differential form of the phase transformation equation. This integration facilitates the control over the entire phase transformation process and the simulation of incomplete transformations. The model is distinguished by its comprehensive functionality, simple form, ease of calculation, and the clear and direct influence of key parameters. Furthermore, it offers a degree of flexibility because each function within the framework is replaceable. The simulation of the TWSME strain and recovery stress hysteresis loop deformation has been successfully conducted, enabling the description of internal hysteresis loops caused by incomplete transformation. The validity of the model is corroborated by comparing it with existing experimental results. Highlights: A constitutive model is introduced that characterizes cyclic degradation phenomena.The model is capable of describing incomplete phase transformation behavior.The recovery stress is also a descriptive object of this model.More accurate simulations are achieved by controlling the rate of phase transformation. [ABSTRACT FROM AUTHOR]

The dynamic interaction between granular flowing masses and rigid obstacles is a complex phenomenon characterised by both large displacements and high strain rates. In case the flowing mass is modelled as a continuum, its numerical simulation requires both advanced computational tools and constitutive relationships capable of predicting the mechanical behaviour of the same material under both fluid and solid regimes. In this paper, the authors employed the open‐source ANURA3D code, based on the Material Point Method (MPM), and a multi‐regime constitutive model. A series of impacts characterised by different velocities, initial void ratios, front inclinations and impacting mass lengths have been simulated. The MPM numerical results are critically compared with those obtained by using a Discrete Element Method (DEM) numerical code. The model capability of simulating material regime transitions, from fluid to solid and vice versa, is shown to be crucial for reproducing the mechanical response of the flowing mass put in evidence by DEM data. [ABSTRACT FROM AUTHOR]

ABSTRACT This study presents a novel approach of intelligent parameter identification (IPI) for a high‐cycle accumulation (HCA) model of sand, which reduces the subjective errors on manual parameter calibration and makes the use of the HCA model more accessible. The technique is based on optimization theory and adopts the cuckoo search algorithm (CSA). To improve search ability and convergence speed of CSA, several enhancements are implemented. First, the improved CSA (ICSA) incorporates quasi‐opposition learning to expand the search space and replaces the original search strategy with a Cauchy random walk to enhance global search ability. Second, an adaptive scaling factor is introduced in the algorithm's control parameters to achieve a better balance between exploration speed and accuracy. Third, a dynamic inertia weight is used to balance the search between global and local spaces when generating new nest positions after abandoning old ones. The performance of the ICSA‐based IPI approach is evaluated by comparing it with the original CSA‐based IPI and manual calibration in determining the HCA model parameters. A comprehensive analysis is also conducted to assess the effectiveness and superiority of each improvement strategy introduced in the ICSA over the original CSA. All comparisons demonstrate that the proposed ICSA‐based IPI method is more powerful and efficient in finding optimal parameters. [ABSTRACT FROM AUTHOR]

ABSTRACT The simulation of the soil–structure interface (SSI) under cyclic loading is critically important in geotechnical engineering. Numerous studies have been conducted to explore the cyclic behaviors exhibited at the SSI. However, existing model evaluations primarily rely on direct comparisons between experiments and simulations, with limited analysis focused on specific behaviors like accumulated normal displacement and stress degradation under cyclic loading. This study proposes and adapts six SSI models, including three nonlinear incremental models and three elastoplastic models. These models incorporate nonlinear shear modulus, critical state theory, and particle breakage effects to enhance their capability to capture SSI behaviors. Utilizing optimization‐based calibration for a fair comparison, the model parameters are fine‐tuned based on the experimental data. Comprehensive assessments including global comparisons and specific behaviors like accumulated normal displacement and stress degradation are carried out to evaluate the models' performance. The results indicate that all models effectively replicate the typical behaviors of SSI systems. By incorporating the particle breakage effect, the models can represent both the reversible and irreversible normal displacements under cyclic loading with better performance. The irreversible normal displacement remains stable and is solely influenced by the soil properties rather than the stress level. Moreover, the models successfully capture the stress degradation under constant normal stiffness caused by the irreversible normal displacement. [ABSTRACT FROM AUTHOR]

Highlights Composites are undergoing extensive research and utilization due to their excellent mechanical properties, driven by human needs. Traditionally, the research methods in materials science predominantly rely on empirical theory or experimental trial and error approaches. However, the increased complexity of composite materials results in a greater intricacy in their mechanical behavior. Consequently, the utilization of traditional research methods may not achieve sufficient efficiency. Materials science is rapidly transitioning into a data‐driven era, with machine learning (ML) emerging as a potent tool to expedite materials development and enhance properties prediction. Significant advancements have been achieved in the application of ML to the study of composite mechanics. In this review article, we elucidate various ML methods employed in the construction of constitutive models for isotropic and anisotropic composites, and delve into the research on construction ML models that leverage input data derived from composite processes, structures, and environmental conditions to predict material mechanical properties. Additionally, we summarize recent noteworthy ML applications in composite design and optimization. Finally, possible prospective viewpoints are proposed for future development, with the aim of providing essential scientific guidance for advancing material science and technology through ML. Machine learning can address complexity in constitutive model of the anisotropic composites. Machine learning predicts mechanical properties of composites well by process and structure. Machine learning enhances efficiency in inverse design to optimize composites. Limitations, challenges, development trends of ML in composites. [ABSTRACT FROM AUTHOR]

In this paper, a new micromechanical hysteresis loop constitutive model of C/SiC composites with different interphases was developed considering the probabilistic‐statistical matrix fragmentation process. The lengths of matrix fragmentation were divided into three types, that is, long matrix fragments (LMFs), medium matrix fragments (MMFs), and short matrix fragments (SMFs). The distributions of the LMFs, MMFs, and SMFs with increasing tensile stress were determined using the probabilistic‐stochastic model by assuming the two‐parameter matrix strength distribution. The micro stress field of the LMFs, MMFs, and SMFs upon unloading and reloading was obtained and adopted to determine the corresponding stress‐strain relations. The interaction of matrix fragmentation lengths, especially for the LMFs with large debonding energy (LDE) and SMFs, was considered in the closed‐form constitutive model and hysteresis‐based inverse tangent modulus (ITMs) damage parameter. Synergistic effects of the fiber volumes, peak stresses, and interface debonding energy on the interface damage state, mechanical hysteresis loops, and related ITMs with small debonding energy and LDE were also analyzed. Comparisons of the mechanical hysteresis loops using the new hysteresis models considering matrix stochastic fragmentation and hysteresis models considering constant matrix fragmentation were also discussed. Experimental cyclic tensile hysteresis loops and unloading/reloading ITMs of C/(PyC)/SiC and C/(PyC+SiC)/SiC composites with different interphase thickness (i.e., t = 300, 600, 1000, and 2000 nm) were predicted using the developed constitutive model. Evolution of the unloading/reloading interface slip ratio was analyzed for different tensile peak stresses. [ABSTRACT FROM AUTHOR]

BACKGROUND: The rapid and accurate detection of moisture content is important to ensure maize quality. However, existing technologies for rapidly detecting moisture content often suffer from the use of costly equipment, stringent environmental requirements, or limited accuracy. This study proposes a simple and effective method for detecting the moisture content of single maize kernels based on viscoelastic properties. RESULTS: Two types of viscoelastic experiments were conducted involving three different parameters: relaxation tests (initial loads: 60, 80, 100 N) and frequency‐sweep tests (frequencies: 0.6, 0.8, 1 Hz). These experiments generated corresponding force‐time graphs and viscoelastic parameters were extracted based on the four‐element Maxwell model. Then, viscoelastic parameters and data of force‐time graphs were employed as input variables to explore the relationships with moisture content separately. The impact of different preprocessing methods and feature time variables on model accuracy was explored based on force‐time graphs. The results indicate that models utilizing the force‐time data were more accurate than those utilizing viscoelastic parameters. The best model was established by partial least squares regression based on S‐G smoothing data from relaxation tests conducted with initial force of 100 N. The correlation coefficient and the root mean square error of the calibration set were 0.954 and 0.021, respectively. The corresponding values of the prediction set were 0.905 and 0.029, respectively. CONCLUSIONS: This study confirms the potential for accurate and fast detection of moisture content in single maize kernels using viscoelastic properties, which provides a novel approach for the detection of various components in cereals. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Deep coal‐rock formations are subjected to complex stress environments characterized by high static stresses and dynamic disturbances. To study the damage, fracture, and energy evolution characteristics of coal‐rock under dynamic–static combined loading, a new multiscale constitutive model for coal‐rock under dynamic–static combined loading is proposed based on micromechanics, and it is implemented into the LS‐DYNA solver. A numerical model of coal‐rock Split Hopkinson Pressure Bar under dynamic–static combined loading is established using LS‐DYNA, and research on the mechanical and energy evolution characteristics of coal‐rock under one‐dimensional and three‐dimensional dynamic–static combined loading is conducted. The results show that under one‐dimensional dynamic–static combined loading, with the increase of precompression, the dynamic peak stress linearly decreases while the combined peak stress linearly increases, and the dissipated energy of the specimen shows a decreasing trend. The fracture patterns of the coal‐rock specimen include internal shear fracture and external tensile fracture, and eventually, these two modes of fracture intersect to form macroscopic mesh cracks. As the axial pressure increases, the degree of specimen fragmentation gradually increases. Under three‐dimensional dynamic–static combined loading, with the increase of preconfining pressure, the stress–strain curve of the specimen will transition from "stress drop" to "stress rebound" after the peak. The peak stress increases with the increase of confining pressure, and the energy dissipation density of the specimen increases first and then decreases with the increase of confining pressure. With the increase of confining pressure, the hoop deformation of the specimen plays a constraining role, and the degree of specimen fracture gradually weakens, and the time of fracture occurrence gradually delays. The research results contribute to revealing the mechanical and energy mechanisms of rockburst disasters in deep coal mines. [ABSTRACT FROM AUTHOR]

A new phenomenological constitutive model is proposed for the prediction of the tensile and compressive behavior of semi‐crystalline and amorphous polymers. The new model modifies the phenomenological model previously proposed by Zhou and Mallick (ZM model) to correctly predict the complex behavior of thermoplastic materials including the linear viscoelastic deformation, the non‐linear viscoelastic deformation, the yielding, the post‐yield strain softening and the post‐yield strain hardening. A validation activity based on literature data has been carried out for polyether‐ether‐ketone (PEEK) and polycarbonate (PC) materials. The new model proved effective in fitting with high accuracy all the phases of the flow stress behavior for the considered materials, across a wide range of strain rates and temperature conditions. Finally, the comparison with Zhu et al., Duan et al., Nasraoui et al., Mulliken‐Boyce and Zhou‐Mallick models showed the better fitting performance of the proposed phenomenological model. Highlights: Formulation of a new phenomenological model.Validation on mechanical test of semi‐crystalline and amorphous thermoplastics.Comparison with different phenomenological models present in the literature.Superior prediction results achieved compared to previously developed models. [ABSTRACT FROM AUTHOR]

Temperature serves as a critical yet elusive factor impacting the mechanical properties of deep rocks. In this work, we shall develop a new micro‐thermomechanical model for rocks based on the Mori‐Tanaka homogenization scheme. Free energy and thermodynamic forces are deduced within the framework of irreversible thermodynamics, including the local stress applied on the mesocracks, damage driving force, macroscopic stress, and entropy. The salient innovation of this study lies in formulating subtle physically based temperature‐dependent friction and damage laws, considering the influence of ambient temperature on the mesocracking in rocks. Through a coupled friction‐damage analysis, a temperature‐dependent quasi‐static strength criterion and analytical stress‐strain‐damage relations are then derived. Physical implications and calibration methods of each parameter in the proposed model are meticulously presented. Furthermore, a semi‐implicit plasticity damage decoupled procedure (SIPDDC) integration algorithm is employed for the numerical implementation of the proposed model. Subsequently, numerical simulations are conducted to obtain the mechanical response of Jinping marble, Beibei sandstone, and Gongjue granite under various real‐time temperature‐confining pressure coupling conventional triaxial compression tests (TP‐CTC). The congruence of stress‐strain curves between model predictions and experimental data validates the robust performance and potential applicability of the proposed model. Plain Language Summary: High ground temperatures have a crucial influence on the stability of deep rocks. Establishing a robust calculation model is paramount for the feasibility and reliability analysis of deep rock engineering. However, incorporating mesocracking mechanisms into such models remains challenging. This paper presents an advanced micro‐thermomechanical model based on homogenization theory, aiming to investigate the macro‐ and micromechanical behaviors of rocks under different ambient temperature conditions. The model innovatively considers the temperature‐dependent characteristics of mesocracking. The model demonstrates satisfactory numerical performance and can effectively capture temperature‐dependent mechanical behaviors of three typical rocks, that is, marble, sandstone, and granite. This work provides a new perspective from a micromechanical standpoint for the theoretical and engineering analysis of deep rock mechanics under high‐temperature and high‐pressure conditions. Key Points: A homogenization‐based micro‐thermomechanical constitutive model is established considering temperature‐dependent friction and damage lawsA temperature‐dependent strength criterion and analytical damage‐stress‐strain relations are derived through cross‐scaling analysisThe model possesses robust numerical performance and shows a promising application prospect in deep rock engineering analysis [ABSTRACT FROM AUTHOR]

Due to the widespread use of carbon nanotube (CNT)‐reinforced polymers in various industries, investigating the dynamic mechanical response of these materials under impact loading is of significant importance. A three‐dimensional viscoelastic (VE)–viscoplastic (VP) constitutive model for CNT/epoxy nanocomposites is developed. A proper rheological model is established using the generalized Maxwell model to represent the VE behavior and propose an exponential function to express the elasto‐VP response. Employing an empirical logarithmic relationship to estimate material properties at different strain rates, the VP behavior is modeled based on the overstress concept. The 3D numerical discretization of the proposed rate‐dependent material model is also carried out to develop a user‐defined material model (UMAT) for the commercial finite element (FE) software of Abaqus. The performed FE simulations based on the proposed rate‐dependent constitutive material can properly capture stress relaxation and hysteresis behaviors of the nanocomposites. Comparing the estimated tensile and shear stress–strain curves through developed material models with experimental measurements, an excellent agreement is observed. Highlights: Tensile/shear properties of CNT/epoxy are measured at three strain rates.An empirical constitutive model is proposed for any arbitrary strain ratesViscoplastic behavior is captured based on over‐stress conceptA 3D incremental form of a viscoelastic–viscoplastic material model is developed. [ABSTRACT FROM AUTHOR]

This paper reports a method to construct the complete constitutive model of carbon fiber‐reinforced plastic (CFRP) by distinguishing the strain rate state and modifying the material stiffness. In quasistatic (low strain rate) compression, the initial nonlinear effect caused by the material defects was described by introducing an nonlinear increasing factor. In dynamic (high strain rate) impact, the nonlinear strengthening effect was described by introducing the dynamic amplification factors of stress and strain based on the reference state. Considering the instantaneous temperature rise obtained from the impact work–temperature generation equation and the influence of temperature on modulus and strength, the coupled thermomechanical constitutive models combining the strain rate effect and the temperature effect were established. The user‐defined material subroutines (VUMAT) were developed, and then these constitutive models were verified by finite element analysis (FEA). Finally, the developed material subroutine was applied to predict the impact penetration of CFRP laminates, and the results show that the opening holes, damage and energy dissipation are in good agreement with the reference experiment. This work comprehensively analyzed the construction method of CFRP constitutive models, which would provide a guidance for the coupled thermomechanical behavior under dynamic impact. Highlights: An anisotropic continuum mechanical constitutive behavior considering strain rate effect and damage evolution behavior was established.A macroscopic anisotropic constitutive model including the coupled impact temperature generation‐mechanical behavior was established.Combined with the incremental finite element method, the three‐dimensional user‐defined material subroutines (VUMAT) were developed and verified.The thermomechanical impact penetration behaviors of CFRP laminates was predicted, and the stress field, temperature field and failure characteristics were visualized. [ABSTRACT FROM AUTHOR]

With the rising demand for hydropower energy, China has built numerous concrete‐faced rockfill dams (CFRDs) with considerable heights. The potential failure pattern of the concrete face slab is the key to the safety of the anti‐seepage system. However, engineers commonly employ an elastic relationship to model the concrete face slab for simplicity, which induces inaccurate estimation of the face slab's stresses, especially under seismic conditions. On the other hand, the existing elastoplastic models for concrete often require complex derivation of the necessary formula and thus are difficult to apply to finite element (FE) analysis. Under the comprehensive action of the upstream water, supporting rockfill, and surrounding mountains, the damage mode of the quasibrittle concrete slab is not a tensile mode but a compressive shearing mode. Therefore, it is urgent to establish an elastoplastic model that is adapted to the actual working environment of the slab and easy to apply. To this end, a generalized plasticity model is developed within the phenomenology modeling concept, which is validated at both the experimental level and application level. The results indicate that three‐dimensional stress‒strain behaviors, such as the strength nonlinearity, prepeak dilatancy, and postpeak softening, can be effectively captured. In addition, the seismic characteristics of a 200‐m high CFRD are numerically investigated. The findings show that the slab's stress accumulation can be reflected during the earthquake and that the final stress distribution conforms to the field observations. The conclusions of this paper provide a reliable reference for the seismic resistance design of CFRDs. [ABSTRACT FROM AUTHOR]

Aging during storage and confinement pressure during launch are the two major loading conditions that affect the integrity of solid rocket motors. In comparison to other component materials, solid propellants, as highly filled composites, have a low modulus and fracture toughness and are therefore common sources of failure. The key to improving the integrity of the solid rocket motor is in assessing the health of the solid propellants during storage or launch. To address this issue, we revised the previous model for the progressive damage viscoelasticity of solid propellants to include the effect of chemical aging during storage and the influence of confinement pressure during launch. Specifically, the increase in relaxation time due to aging and the nonequilibrium volume dilatation characteristics under triaxial tension and compression of solid propellants have been considered. To validate the developed model, standard relaxation tests and uniaxial tensile tests on solid propellants without aging were used to calibrate the model parameters. Furthermore, the model was validated by comparison with uniaxial tensile tests under confined pressure after aging and well predicts the aging temperature/time‐dependent mechanical responses of solid propellants. After validation, the developed model was used to study the influence of confinement pressure on microscopic damage evolution and macroscopic volume expansion. Overall, the developed model can be used for the analysis of the integrity of the solid rocket motor after the aging process. [ABSTRACT FROM AUTHOR]

Steel fiber reinforced concrete (SFRC) structures have been widely adopted and attracted great research attention due to their excellent performance in resisting tension and flexure bending. However, the existing analytical and numerical analyses of SFRC structures rely mainly on the experimental data of material tests, thereby being suitable for a case‐by‐case basis. This is due to the lack of a general and reliable constitutive material model for SFRC, which analytically considers the fiber‐dependent parameters such as fiber geometry, fiber stiffness, and interface properties of fibers and concrete matrix. This study presents an approach to modify the concrete plastic damage model to represent the SFRC material constitutive relations for simulating the structural behavior of SFRC. In this approach, the general procedure to integrate the bridging effect of fibers through the pull‐out mechanism into the constitutive relation of SFRC was proposed. The comparison between the numerical and experimental results was conducted to verify the reliability of the proposed model. The results demonstrated the proposed model could well represent the material performance of SFRC and the numerical simulations could capture reasonably the effect of the volume fraction, geometry, and properties of fibers on the structural response of SFRC. [ABSTRACT FROM AUTHOR]

A modular hypoplastic constitutive model for granular soils under non‐cyclic loading A new hypoplastic constitutive model with modular formulation is presented. The modular structure allows the application of the material model already with very little material information under restriction of the soil effects to be reproduced. The more material information available, the better the stress‐strain behavior of the material can be represented. The presented material model is compared with the results of simple laboratory tests for validation. In addition, further laboratory tests are simulated to show the performance of the material model. [ABSTRACT FROM AUTHOR]

With the increasing depth of engineering in rock masses, the issue of significant rheological deformation becomes notably prominent. To accurately characterize the deformation and failure behavior of the surrounding rock near the goaf in deep small coal pillars, we have developed a viscoelastic–plastic constitutive model that takes into account the initial stress associated with creep. This model builds upon an existing viscoelastic–plastic constitutive framework and is implemented numerically using C++ in the FLAC3D. The Oedometer test method is used to check the creep components and the calculated parameter (η/G) ensure convergence of numerical operations. We conducted both pre‐improvement and post‐improvement tests of the constitutive model in a simple numerical analysis of roadways. The enhanced model demonstrates improved accuracy in deviational stress calculations and proves suitable for modeling deep, soft roadways. Furthermore, we applied the improved model to simulate actual working conditions at Zhaozhuang Mine, where mining operations near the working face induce a fracture zone of approximately 3 m in the small coal pillar located at the goaf's edge. The new model closely aligns with the observed results, further validating its suitability for tunneling along the goaf. Tunneling and mining activities result in significant deformation at various locations, including the shoulder socket of the working face, the top angle of the coal pillar, and the bottom angle of the floor. The crushing zone at the working face extends up to 4 m. Rheological effects transform the triangular elastic core, from its original high‐pressure elastic state to a fracture and plastic zone in the deep coal. Stress in deep coal is transmitted along the triangular elastic core. Numerical simulation results closely match the excavation profile of the tunneling, providing valuable insights into the impact of mining activities. This study can provide reference for deformation of similar geological conditions and engineering situation. [ABSTRACT FROM AUTHOR]

Hot compression experiments with the deformation temperatures of 750–950 °C and the strain rates of 0.01–10 s−1 are carried out on a Gleeble‐3500 thermal‐mechanical simulator. The flow behavior and dynamic recrystallization (DRX) mechanism of the Cu‐Ti‐Fe alloy are systematically studied under different hot deformation conditions. According to the curves of flow stress and work hardening rate, the DRX critical condition of the alloy is obtained, and the critical stress value of DRX is small under high‐temperature and low‐strain rate. After fitting, the logarithmic values of the critical stress and critical strain have a linear relationship with lnZ, which indicates that the alloy is more prone to DRX at high temperatures and low‐strain rates. The Arrhenius constitutive model of the alloy is established, the linear correlation coefficient (R2) is 0.984. Combined with the microstructure of Cu‐Ti‐Fe alloy, the microstructure evolution characteristics and DRX mechanism are elucidated. The dominant mechanism of the alloy under the deformation temperature of 750–950 °C is the DRX mechanism. The low‐angle grain boundaries (LAGBs) transform into high‐angle grain boundaries (HAGBs) and continuous dynamic recrystallization (CDRX) grains form. Abundant dislocations gather near the HAGBs, causing grain boundaries to protrude. High‐temperature conditions make the dislocations disappear, forming discontinuous dynamic recrystallization (DDRX) grains. [ABSTRACT FROM AUTHOR]

The significance of the mechanical properties of solid propellant during the curing process lies in their contribution to stress‐strain calculations of viscoelastic engineering materials and the analysis of structural integrity of solid rocket motor charges. In order to study the Constitutive equation of the nitrate ester plasticized polyether (NEPE) propellant during the curing process, indentation creep tests were carried out on the NEPE propellant, and the viscoelastic constitutive model of propellant with curing reaction at 50 °C and atmospheric pressure was studied. Firstly, based on the viscoelastic theory, the experimental principle of indentation creep test is deduced, and indentation creep tests are carried out for propellants with different curing degrees. Then, based on 2S2P1D (2 Springs, 2 Parabolic elements, 1 Dashpot) model and time‐temperature equivalence principle, the indentation test data are processed, and the complex modulus master curve of propellant with different curing degrees is established, and the influence of curing reaction on viscoelastic properties of propellant is analyzed, so as to better understand the response characteristics of propellant system during curing. The results show that the 2S2P1D model has a good fitting effect for the master curve in low frequency period, the fitting error is controlled within 10 %, and the correlation coefficients are all above 0.95. With the curing reaction, the complex modulus gradually increases, while the change rate gradually decreases. And it tends to be stable on the seventh day. [ABSTRACT FROM AUTHOR]

Buckling of the longitudinal rebar is one of the main forms of plastic hinge failure in reinforced concrete (RC) columns after an earthquake. This rebar buckling significantly impacts the seismic bearing capacity and energy dissipation capacity. To restrain the development of longitudinal rebar buckling behavior and delay the degradation of lateral strength in RC columns, this paper developed a new type of buckling restraint rebar (BRR) consisting of three components: longitudinal rebar, a restraint sleeve, and foam material. First, the BRR mechanical properties under compression and tension‐compression cyclic loading were obtained through quasi‐static loading tests. Then, the BRR compression and tension‐compression cyclic loading processes were numerically simulated based on ABAQUS finite element software. The simulated results were compared with the test results. Finally, a stress–strain constitutive model for this new BRR was proposed based on this study. Results showed that the restraint sleeve could significantly enhance the lateral stiffness and the bearing capacity of longitudinal reinforcement after yielding. The compressive performance of BRR was mainly affected by the length and wall thickness of the sleeve. The cyclic performance was mainly affected by the length of the sleeve and the clearance between the sleeve and the reinforcement. The BRR constitutive model proposed in this paper can accurately reflect the influence of restraint sleeves on the stiffness of longitudinal reinforcement after yielding. [ABSTRACT FROM AUTHOR]

In this work, a unified damage model is proposed for describing the mechanical behavior of concrete under monotonic loading and fatigue loading. Based on the micro‐meso stochastic fracture model (MMSF), the multiscale energy dissipation within the microspring is investigated. The rate process theory and a crack hierarchy model are employed to describe the nanocrack growth rate and crack number, respectively. It is found out that the fracture strain of the microspring can be derived from the energy dissipation analysis. The expression of the stochastic damage evolution law is changed to "energy dissipation threshold" instead of "fracture strain." The new model can describe different damage evolution forms under monotonic and fatigue loading with the same parameters. The mechanisms of different damage evolution laws under different loading modes are analyzed in detail. Finally, a numerical example is presented to verify the proposed model. [ABSTRACT FROM AUTHOR]

Extracting juice from sugarcane is a complex and nonlinear process. It is very important to comprehend mechanical properties and constitutive model of the milled mixture of sugarcane for understanding sugarcane crushing process. In this paper, mechanical properties of the milled mixture were investigated by uniaxial compression tests, repeated loading tests and direct shear tests. The elastic–plastic constitutive model was established by using isotropic elastic materials and Modified Cam‐Clay model based on phase transition state. Both Poisson's ratio and Young's modulus of the milled mixture were proportional to the loading stress; the compression index and swelling index are 2.23 and 0.10, respectively; and the cohesive force and friction angle are 25.25 kPa and 21.63°, respectively. At last, the proposed constitutive model was verified by uniaxial compression tests. This paper can provide a theoretical basis for the study of mechanism and simulation of sugarcane crushing processes, and is of guidance for the improvement of sugar production process and equipment. Practical applications: In this article, the prepared cane and bagasse are collectively called the milled mixture of sugarcane, which includes solid fiber, juice, and air. The interaction of three components of milled mixture can lead to difficulties in extracting juice, an increase in processing energy consumption and other undesirable conditions. In this paper, the mechanical properties and constitutive model of milled mixture of sugarcane are studied. This research can provide a new method for the simulation of sugarcane milling process, and has enlightening significance for the optimization of crushing equipment and technological parameters to improve juice extraction efficiency. [ABSTRACT FROM AUTHOR]

The dynamic compressive mechanical performance of coral aggregate concrete (CAC) has been studied by the servo‐controlled true triaxial testing machine (TAWZ‐5000/3000), the failure modes and the stress–strain curves were obtained under various loading conditions. The effect of strain rates and the constant lateral pressure on the strength, deformation capacity, and failure modes of CAC were analyzed according to the results obtained from the test. The results show that the lateral pressure significantly changes the failure mode while the strain rate only affects the degree. The strength and deformation capacity will improve with the increase of strain rate and lateral pressure, and the lateral pressure diminishes the strain rate effect on mechanical properties. A 5‐parameter empirical dynamic failure criterion was established based on the William‐Warnke criterion. Finally, a 2‐stage dynamic multiaxial compressive constitutive model obeying the Weibull and Lognormal statistical distributions was established, and the model had well‐fitting results with the experimental results. [ABSTRACT FROM AUTHOR]

Herein, isothermal compression experiments are conducted on EA4T steel at 970–1170 °C, with strain rates of 0.01–1.0 s−1 and a strain of 0.2–0.8 s−1. Based on the experimental data, a high‐temperature constitutive model is developed for EA4T steel. The activation energy of dynamic recrystallization (DRX) is calculated to be 383 666 J mol−1, and the correlation coefficient and root mean square error between the results of the constitutive model and experimental results are 0.9943 and 4.6823, respectively. The average grain size for each deformation condition is determined using the linear‐intercept method. The grain growth model widely used in cellular automaton (CA) simulations is found unsuitable for EA4T steel. Therefore, a modified CA model of DRX behavior suitable for EA4T steel is developed. The nucleation rates and solute drag effect coefficients under different deformation conditions are determined. Furthermore, simulations are performed under other deformation conditions using the CA model. The simulated results for the average grain size, microstructure morphology, and DRX fraction agree well with the experimental results. The reason for the deviation between the observed and simulated DRX fractions is also explored. [ABSTRACT FROM AUTHOR]

In this paper, creep tests were carried out on HTPE/AP/Al/RDX propellant specimens to investigate the effects of stress level and temperature on their creep behavior and to investigate the creep mechanism. Higher stresses and temperature can cause greater creep strain in the propellant, ultimately leading to its destruction. On this basis, the creep master curve was further obtained based on the Time‐Temperature Superposition Principle (TTSP), extending the creep investigation time range to 1010 s. Based on previous experience, some explorations have been made on constitutive equations. The burgers model fits the creep behavior under different conditions more closely, while the Norton model has higher stress sensitivity. [ABSTRACT FROM AUTHOR]

A robust and concise implicit stress integration algorithm of elastoplastic models is presented. It does not require the loading/unloading estimation and analytical derivation operation for the stress update. First, the elastoplastic stress update problem is recast into an unconstrained minimization problem by utilizing the smooth function to bypass the loading/unloading estimation. Then, the object problem is solved by the line search method instead of the Newton method for better convergence. The consistent tangent operator is evaluated by the complex step derivative approximation without the subtraction cancellation error, which provides the quadratic convergence rate of global iteration. The rationality of the numerical consistent tangent operator is validated by the one obtained by the analytical derivation. A recently developed non‐orthogonal elastoplastic (NEP) clay model is implemented using the new algorithm. The algorithm is confirmed through comparing the numerical solution and the analytical one for a cavity expansion problem. The algorithm performance is assessed based on a series of geotechnical boundary value problems. It is found that the new algorithm is more robust than the one employed by ABAQUS. The source code of the model implementation can be downloaded from https://github.com/zhouxin615. [ABSTRACT FROM AUTHOR]

A fractional constitutive meta‐model for the mechanical behavior of rocks is proposed to bypass complex integration algorithms and consider the uncertainty of model/material parameters. First, a physics‐induced database is constructed with the aid of a fractional constitutive model and two developed input–output strategies. Then three machine algorithms (i.e., random forests, extreme gradient boosting, and multilayer perceptron) together with two input–output strategies are employed to formulate six different meta‐models. The grid‐search and five‐fold cross‐validation methods are utilized to optimize key hyperparameters of meta‐models. Through the comparisons of evaluation metrics and prediction results, the multilayer perceptron algorithm with strategy II becomes an optimal combination to construct the meta‐model. The results of the feature's importance and sensitivity analyses indicate that the parameters' influences in this data‐driven paradigm are in line with physical reality. The effectiveness of the proposed meta‐model is validated by comparing the predicted results with experimental observations from the literature. Additionally, the uncertainty analyses from the meta‐model and material/model parameters can be conducted based on a linear regression model and the Monte Carlo simulation. The study results show that the presented meta‐model based on physics‐guided synthetic data has the potential to replace the general fractional constitutive model. [ABSTRACT FROM AUTHOR]

The physical mechanism underlying the mechanical behavior of glassy polymers has been studied over decades but remains a long‐standing issue. A consensus view achieved is that the yield, flow, and stress relaxation behaviors are due to structural relaxation in the polymer mainly caused by chain conformation transitions. This is the key physical idea behind the many existing elastic–plastic constitutive models for glassy polymers. In this paper, such a constitutive model was employed for predicting and analyzing the stress relaxation of a glassy polymer. It is found that the model works well in predicting the pre‐yield stress relaxation but significantly underestimates the post‐yield stress relaxation. As considering the chain conformation transition alone leads to a dilemma for the model to concurrently represent the yield/flow and stress relaxation behaviors, the model was extended to incorporate an additional structural relaxation mechanism assumed to originate from the dissociation of weak linkages in the chain network. The extended model succeeds in concurrently representing the yield/flow, and stress relaxation behaviors in the whole deformation region, of which the reasons were analyzed. The knowledge revealed in this paper is instructive and may shed new light on understanding the structural relaxation and mechanical behavior of glassy polymers. [ABSTRACT FROM AUTHOR]

A method for identifying the relaxation modulus or creep compliance of composite propellant based on indentation technique is proposed, which can rapidly and nondestructively measure the mechanical properties of solid rocket motor grain in storage. According to viscoelastic indentation theories, a constitutive model for conical indentation is derived to predict the mechanical parameters of composite propellants. The indentation test with different loading rates and the traditional tensile stress relaxation test for a certain PBT composite propellant were carried out to verify the feasibility of the proposed method. The results show that the prediction results calculated by the constitutive model are in good agreement with the load‐displacement curves of the indentation test, and the mechanical parameters identified by the constitutive model are similar to those parameters fitted by the tensile stress relaxation test. Relevant methods and conclusions can provide a reference for structural analysis and storage life prediction of solid rocket motors. [ABSTRACT FROM AUTHOR]

In this paper, the Barton–Bandis model for rock joints is extended to cyclic loading conditions, without any new material parameter. Also developed herein is an implicit solution algorithm for the extended Barton–Bandis model, which can also be used for the original Barton–Bandis model for which an implicit algorithm has been unavailable. To this end, we first cast the Barton–Bandis model into an incremental elasto‐plastic framework, deriving an expression for the elastic shear stiffness being consistent with the original model formulation. We then extend the model formulation to cyclic loading conditions, incorporating the dependence of shear stress and dilation on the joint position and the shearing direction. The extension is achieved by introducing a few state‐dependent variables which can be calculated with the existing material parameters. For robust and accurate utilization of the model, we also develop an implicit algorithm based on return mapping, which is unconditionally stable and guarantees the satisfaction of the strength criterion. We verify that the proposed model formulation and algorithm produce virtually the same results as the original Barton–Bandis model under monotonic shearing conditions. We then validate the extended Barton–Bandis model against experimental data on natural rock joints under cycling loading conditions. The present work thus enables the Barton–Bandis model, which has been exceptionally popular in research and practice, to be applicable to a wider range of problems in rock mechanics and rock engineering. [ABSTRACT FROM AUTHOR]

Numerical prediction of landslide runout and deposition is important for estimating landslide risk and developing mitigation plans. The choice of a suitable model and its parameters and a confident calibration strategy are crucial for numerical simulations. Here, we evaluated two constitutive models with a three‐dimensional smoothed particle hydrodynamics (SPH) method by simulating the catastrophic 11 October 2018 Baige landslide. The results indicate that both the soil mechanic and fluid models can capture the dynamic runout and deposition morphology while using different values of input parameters. A point‐wise comparison of deposit elevation can minimize the calibration error. Numerical models were constrained accurately by utilizing both the static observation data and dynamic seismic signals. The effects of friction on deep‐seated landslides motion and deposition are more significant than cohesion. The 3D model includes the effects of shear stresses and velocities inside the material body, resulting in a reduced friction coefficient compared to the 2D model (e.g., depth‐averaged model). Our study highlights the potential of the 3D SPH method for modeling large‐scale complex landslides. Plain Language Summary: Landslides belong to a type of earth surface process recognized by their high damage potential. Computer models can simulate the landslides' movement to predict speed, forces, and deposition, which can help to delineate areas at risk and to design mitigation measures. We simulated the 2018 Baige landslide in China with a method known as smoothed particle hydrodynamics (SPH), to test whether it is suitable for landslide simulation and to investigate protocols for model calibration when including seismic data in addition to information on the landslide's deposit. In this method, the landslide body is represented by millions of small, moving, interacting particles, which offers advantages over established models in terms of computation time and details in the simulation. We find that SPH is suitable for modeling large‐scale natural landslides. The seismic data are more valuable in the model calibration than landslide deposit observations. The new approach yields landslide simulations that deliver more details on particle velocities within the landslide body, and their spatial and temporal distribution. These details can be used to infer the properties of landslides during the sliding process, which helps to better understand landslides in general and to set up models for events where little data are available. Key Points: A three‐dimensional mesh‐less graphics processing unit‐accelerated smoothed particle hydrodynamics formulation is suitable for modeling large‐scale natural landslidesThe selection of an appropriate constitutive model depends on the landslide features and materialsIncluding dynamic seismic signals into numerical model calibration routines in addition to topographic changes improves calibration [ABSTRACT FROM AUTHOR]

The mechanical properties of optically clear adhesive (OCA) films can be anisotropy and viscoelasticity, and they are distinguished from conventional linear elasticity and hyper‐elasticity. These properties should be considered to analyze the interfacial stress, which plays an important role in evaluating the failure of a structure containing OCA. Based on well‐designed systematical experiments in the material's principal axes, a phenomenological constitutive model of OCA has been proposed in a transversely isotropic and rate‐dependent form. For the application to large deformation cases, the constitutive model was developed by using true stress and true strain. Results show that the well‐known assumption of volume‐incompressibility is not appropriate for OCA, and Poisson's ratio can vary with the loading rate and the current strain. Considering that the mono‐axial mechanical behaviors along the material's principal axes present strong non‐linearity, an incremental three‐dimensional constitutive model has been developed for finite element method (FEM) implementation. By comparing with traditional isotropic elastic and hyperelastic models, numerical examination results show that the proposed constitutive model can give a more accurate description of experimental stress–strain curves. [ABSTRACT FROM AUTHOR]

The mechanical behaviors of TB991 weld sealant under cyclic loading conditions were experimentally investigated. The evolution of relaxation stress, cyclic softening, and dissipated energy was evaluated with the effect of strain amplitude and mean strain. The experimental results showed that the stress–strain response curves of the first loading‐unloading and cyclic loading‐unloading were significantly different. The phenomenon of stress relaxation and cyclic softening occurred under cyclic strain loading conditions. Furthermore, the relaxation stress and dissipated energy decreased rapidly during the initial cyclic loading and then steadily decreased with the increase of cycle number, while the cyclic softening increased rapidly at first and then steadily. Besides, a viscoelastic constitutive model was proposed which can describe the different shapes of stress–strain curve between the initial loading‐unloading and the cyclic loading‐unloading and also considers the cyclic stress relaxation and cyclic softening of the materials under cyclic loading condition. Comparisons between the numerical results and the experimental data demonstrated that the proposed model can better describe the mechanical behavior of TB991 weld sealant under cyclic loading conditions. TB991 weld sealant was experimentally investigated under cyclic loading conditions.The evolution of relaxation stress, cyclic softening, and dissipated energy was investigated.A constitutive model was proposed to describe the mechanical behavior of the material under cyclic loading conditions.The proposed model can consider the cyclic stress relaxation and cyclic softening of the materials. [ABSTRACT FROM AUTHOR]

Non‐shock ignition of explosions in solids by dynamic loading is a key topic in the field of explosives safety research. Cracks and other damage in polymer‐bonded explosives greatly affect non‐shock ignition. In this study, we developed a modified set of constitutive models that incorporate heterogeneity of initial cracks and failure of damaged granules, both of which can affect the thermodynamic response and non‐shock ignition of condensed explosives. Moreover, the models were used to predict the distribution of cracks and damage under dynamic compression. The calculated results were in good agreement with experiment, which confirmed the validity of the models. [ABSTRACT FROM AUTHOR]

In order to study the mechanical behavior of solid rocket motor charge bonding interface under uniaxial tensile loading, the bonding interface of HTPB propellant/liner/insulator during uniaxial tensile process was scanned and reconstructed based on micro‐CT in‐situ loading, and the variation of porosity and interface debonding rate with strain was analyzed. A damage‐containing constitutive model based on the evolution of meso‐characteristic parameters was established for bonded interfacial components. The experimental analysis shows that the initial defects have a great influence on the location and evolution direction of the interface damage, and the interface damage can be quantitatively characterized by the interface debonding rate and porosity, and the interface debonding rate can better reflect the damage evolution process of micro‐pores and cracks near the propellant/liner interface. The damage‐containing constitutive model based on the evolution of mesoscopic characteristic parameters can effectively establish the structure‐activity relationship between mesoscopic parameters and macroscopic mechanical properties, and can predict the mechanical behavior of charge interface. [ABSTRACT FROM AUTHOR]

High strength steels are increasingly used in several areas of construction offering structural solutions with a high strength‐to‐weight ratio. Safe fire design of these structures relies heavily on accurate predictions of mechanical properties of the material with temperature. This paper presents the results obtained using Machine Learning (ML) algorithms to predict the mechanical properties, including ultimate tensile strength, yield strength and elastic modulus, of high strength steel plate material. The mechanical properties collected from the literature experimental tests show a high degree of scatter, implying that they are influenced significantly by various factors such as the testing method, manufacturing process and chemical composition. However, the current methods for predicting the mechanical properties of high strength steels at elevated temperatures by using 'reduction factors' adopted by the structural design codes do not consider these effects and may lead to inaccurate predictions. These deficiencies are overcome by using a ML‐based prediction method, where the effects of the chemical composition on these reduction factors are considered. Deep Neural Networks is trained to predict the mechanical properties with temperatures. The ML‐based method together with the obtained results are presented where it is shown that the trained algorithm gives an excellent correlation coefficient with very small error value. [ABSTRACT FROM AUTHOR]

Concrete exhibits a different deformation behavior in tension and compression when subjected to uniaxial and biaxial loads. It also reveals crack‐opening and crack‐closing effects under cyclic loads. This paper discusses a gradient‐enhanced continuum damage model to investigate the deformation and damage behavior of concrete subjected to cyclic and multiaxial loading conditions. An activating variable introduced in the model distinguishes the multiaxial stress states. A single damage criterion that relates the history variable to the equivalent strain limits the elastic domain. The evolution of internal variables confirms their thermodynamic consistency. The gradient enrichment of equivalent strains leads to proper localization of deformation. Comparison of numerical predictions with relevant experimental data and some previous models validates the capability of the model to describe softening/crack‐closure behavior under various loading. Application of the model to fracture problems demonstrates the ability of the model to describe damage initiation and propagation, and its localization. [ABSTRACT FROM AUTHOR]

The Elastoplastic Hysteretic Small Strain (EPHYSS) model is an advanced elastoplastic model as a result from the combination of the Hysteretic Quasi‐Hypoelastic (HQH) model that considers strain‐induced anisotropy and can reproduce the nonlinear reversible, hysteretic and dependent on recent history soil behavior, and the Cap‐Cone Hardening Soil Modified (HSMOD) model that can reproduce soil plastic behavior. EPHYSS model uses state variables that define different short and long‐term memory levels which provide it with robustness for the reproduction of soil hysteretic behavior and confers it a great versatility and adaptability to experimental results. It also corrects some inconsistencies of the Hardening Soil with Small Strain Stiffness (HS‐SS) model of Plaxis whose effects can have a considerable influence on the numerical simulations of boundary problems. The performance of EPHYSS and a comparison with the HS‐SS model is presented in some experimental and numerical tests, and in a boundary value problem of a large excavation in Barcelona. [ABSTRACT FROM AUTHOR]

There is considerable potential for data‐driven modelling to describe path‐dependent soil response. However, the complexity of soil behaviour imposes significant challenges on the training efficiency and the ability to generalise. This study proposes a novel physics‐constrained hierarchical (PCH) training strategy to deal with existing challenges in using data‐driven models to capture soil behaviour. Different from previous strategies, the proposed hierarchical training involves 'low‐level' and 'high‐level' neural networks, and linear regression, in which the loss function of the neural network is constructed using physical laws to constrain the solution domain. Feedforward and long short‐term memory (LSTM) neural networks are adopted as baseline algorithms to further enhance the present method. The data‐driven model is then trained on random strain loading paths and subsequently integrated within a custom finite element (FE) analysis to solve boundary value problems by way of validation. The results indicate that the proposed PCH‐LSTM approach improves prediction accuracy, requires much less training data and has a lower performance sensitivity to the exact network architecture compared to traditional LSTM. When coupled with FE analysis, the PCH‐LSTM model is also shown to be a reliable means of modelling soil behaviour under loading‐unloading‐reloading and proportional strain loading paths. In addition, strain localisation and instability failure mechanisms can be accurately identified. PCH‐LSTM modelling overcomes the need for ad‐hoc network architectures thereby facilitating fast and robust model development to capture complex soil behaviours in engineering practice with less experimental and computational cost. [ABSTRACT FROM AUTHOR]

An elasto‐plastic constitutive model is proposed to account for the effect of principal stress rotation that commonly occurs and significantly influences soil behavior. The model is based on a concept of adding plastic strain increments obtained from two mobilized planes: a plane of maximum shear stress which swings as the principal stress rotates, and a horizontal plane which is spatially fixed. Models based on the plane of maximum shear stress alone are particularly sensitive to horizontal effective stress ratio K0 (=σ′x/σ′y), whereas the proposed model gives a similar skeleton behavior for soils at the same density and mean effective stress, regardless of the value of K0, as observed in laboratory tests. The model is firstly calibrated by data from drained and undrained monotonic and cyclic Direct Simple Shear (DSS) tests on K0‐consolidated specimens of Nakdong River sand in loose and dense states. The capability of the proposed model in modeling of the conventional liquefaction effects: initial shear stress condition α (=τ′xy/σ′y) with Kα corrections, and initial confining stress condition σ´y with Kσ corrections, is also emphasized in this paper. [ABSTRACT FROM AUTHOR]

Plane‐stress and shell macromodels are often preferred to analyze masonry structures because of their numerical efficiency. However, they often misestimate the hysteretic behavior of the structures. Additionally, due to the nature of smeared cracks, the cracks may be diffused. This article proposes a new orthotropic model, which focuses on the cyclic, nonlinear behavior of brick masonry structures. The model adopts a total‐strain based rotating crack approach. It describes tensile and compressive failure in the rotating principal directions, while including indirectly shear failure through an internal iterative algorithm. Two distinctions are made regarding the tensile postpeak and unloading/reloading behavior based on the crack orientation at crack initiation: a steep softening branch and secant unloading are adopted when the crack angle corresponds to in‐plane flexural failure, and a softening branch and bilinear unloading are adopted when the crack angle corresponds to diagonal shear failure. Bilinear unloading/reloading is adopted in compression, resulting in a cyclic behavior resembling shear. The constitutive model was implemented in a finite element software and validated against experimental results. The numerical simulations reproduced well the experimental outcomes in terms of envelope load‐displacement curve and hysteretic behavior, while simultaneously they resulted in localized damage, representative of the experimental crack patterns. [ABSTRACT FROM AUTHOR]

The geomaterials with original anisotropic properties formed in the natural process are usually simplified as a kind of cross‐anisotropic material. The spatial location of the depositional plane (DP) and the effective spatial mobilized plane (ESMP) in physical space is closely related to anisotropic properties; thus, the inclined angle between DP and ESMP is taken as a primary parameter governing the strength degree of geomaterial anisotropy. According to the concept of ESMP, the frictional capacity can be more effectively mobilized when the inclined angle between DP and ESMP is larger, inducing a higher stress strength. In this study, a new stress strength formula is proposed for geomaterials, which takes the cross‐anisotropic properties into account. The transformation strategy can be regarded as a strength criterion describing the convert of transversely isotropic behavior formula into an isotropic von Mises criterion formula. Based on the cross‐anisotropy strength criterion, the transformed stress (TS) equation can be derived by transforming the cross‐anisotropy stress space to the isotropic stress space. By using the proposed TS method, it is convenient to convert the traditional two‐dimensional (2D) constitutive models on the basis of the Von‐Mises criterion to the general three‐dimensional (3D) models considering cross‐anisotropy. Comparing the predicted and the tested results of strength and stress‐strain relationship tests for geomaterials under the true triaxial loading condition, the validity and the applicability of the proposed TS method with related criterion can be ensured. [ABSTRACT FROM AUTHOR]

The Cosserat continuum is very effective in regularizing the ill‐posed governing equations of the Cauchy/Maxwell continuum. An elasto‐plastic constitutive model for the linear formulation of the Cosserat continuum is here presented, which features non‐associated flow, hardening/softening behaviour and multiple yield and plastic potential surfaces, whilst linear hyper‐elasticity is adopted to reproduce the recoverable response. For the definition of the yield and plastic potential functions, the equivalent von Mises stress is formulated using energy considerations and the theory of representations, the latter being also used to retrieve an expression for the Lode's angle. The recent Generalized classical criterion is then used to define the yield and plastic potential functions so that Lode's angle‐dependent deviatoric sections can be used. [ABSTRACT FROM AUTHOR]

In this paper, a new constitutive model which can model the thermo‐mechanical behaviors of functionally graded shape memory polymer (SMP) beam is established. The kinematic equation was established based on the SMP constitutive equation further derived and Euler–Bernoulli beam theory. The material parameter equations were established by taking the volume fraction of carbon nanotubes (CNT) as the gradient based on the material parameter equations of SMP and properties of functionally graded materials. According to the constitutive model, the simply supported beam was taken for example to be solved and simulated by using the virtual work principle. The results show material parameters properties, deflection properties, stress properties and shape memory properties of CNT/carbon nanotube/polyurethane (PU) functionally graded beam and some conclusions are concluded. This work shows the thermo‐mechanical behavior of CNT/PU functionally graded beam, and it provides a theoretical basis for the practical application of functionally graded SMP materials. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (NGH) is widely distributed in marine sediments and continental permafrost, which is a promising energy resource. The sustainable and safe exploration and production of NGH requires fully understanding of its mechanical behaviors, which is still a challenge to our community. In this paper, a statistical damage constitutive model named SC‐SDCM is developed for NGH sediments. The NGH sediments are regarded as two phases: the matrix phase of solid mineral grains, pore fluid, and gas, and the inclusion phase of hydrate crystal. The effective elastic parameters of such two‐phase composite are estimated by self‐consistent method (SC) according to the equivalent inclusion principle of micromechanics. The mesoscopic element strength of the NGH sediments is described by the Weibull statistical distribution and the damage theory of composite materials. And then combined with the Drucker‐Prager failure criterion of microelement, the damage constitutive model of NGH sediments is established. The new SC‐SDCM is tested to be reliable and robust by triaxial experimental observations on artificial cores and naturally occurring samples under different confining pressures and hydrate saturations. The SC‐SDCM could properly describe the stiffness, peak strength, and strain softening properties of the NGH sediments. Moreover, the predictions of SC‐SDCM are closest to the experiment observations compared to several published constitutive models, especially for the near‐ and after‐damage stages with relatively high hydrate saturation. [ABSTRACT FROM AUTHOR]

Although advanced modeling techniques such as the finite element method (FEM) have been used successfully in dynamic site response analysis, the high computational expense has hindered the incorporation of input parameter uncertainty in such analysis. Thus, when the variation of the peak ground acceleration (PGA) at the ground surface, which is the outcome of the site response analysis, has to be evaluated in the face of uncertainty, a surrogate model such as Response Surface Method (RSM) model is often used in lieu of the FEM model. In this paper, the RSM surrogate model was implemented in the context of seismic site response analysis to evaluate the variation (or uncertainty) of the PGA due to the propagation of input parameter uncertainty. The engineering implication of the variation of the surface PGA is significant as this knowledge is required for such tasks as reliability analysis of soil liquefaction and probabilistic seismic risk analysis. To derive the RSM model specifically for a site response analysis, a parametric study of the dynamic site responses using FEM code ABAQUS with the modified Davidenkov soil constitutive model implemented as a user‐defined material subroutine is first conducted. The input parameters, including the soil profile, soil properties, and input ground motion, in a typical dynamic site response analysis are then characterized and screened for their suitability to be included in the RSM model. For a given site response problem in the face of uncertainty, representative "samples" are taken for site response analysis using ABAQUS, and the analyses are carried out and finally the response surface is constructed using the outcomes of the ABAQUS numerical experimentations. The accuracy of the developed RSM model is then validated using the results of ABAQUS on cases not used in the development of the RSM model. Once the RSM model is deemed satisfactory, the reliability‐based formulation for evaluating the mean and standard deviation of the surface PGA is established. Example is provided to illustrate the RSM approach for dynamic site response analysis in the face of input parameter uncertainty. [ABSTRACT FROM AUTHOR]

The shape memory polymers (SMPs) and shape memory alloys (SMAs), as typical smart materials, have got enormous attention in the fields of aerospace, microsystems, and biomedicine due to their superior shape memory properties. Combining the high strength of SMAs and the large deformation of SMPs, the shape memory polymer composites with the shape memory alloys fibers (SMPC‐SMAs) formed by SMP matrix and SMA fibers have the dual advantages of SMAs and SMPs. For the different loading conditions, the mechanical behaviors of the SMPC‐SMAs are investigated in this work, by combining with the mechanics of composite materials and the constitutive models of SMPs and SMAs. Compared with the mechanical behavior of pure uniaxial loading, the influence of temperature changes on the phase transition of the material is considered under different constraints. Compared with mechanical behaviors of pure SMAs and pure SMPs, the thermomechanical behaviors of the SMPC‐SMAs are discussed and simulated considering the coupling of the phase transition of SMPs and SMAs. And the effects of different fiber content and different pre‐strain on the behaviors of such SMPC‐SMAs are finally discussed, respectively. The results showed that different mechanical properties for SMPC‐SMAs are displayed; such materials not only can maintain the normal shape memory effect but also have the greater strength, which will be a better engineering application prospect. [ABSTRACT FROM AUTHOR]

In order to study the effects of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether (NEPE) propellant, compressive tests were conducted under various confining pressure conditions and strain rates using a new-designed active gas confining pressure testing machine. The stress-strain curves and mechanical properties of the NEPE propellant under varying confining pressure conditions and strain rates were obtained. The results show that the compressive mechanical properties of the NEPE propellant are remarkably influenced by the confining pressure and strain rate. The compressive strength under confining pressure is obviously larger than those without applied confining pressure. With the coupled effects of the confining pressure and strain rate, the compressive strength under 5.4 MPa and 6.67× 10-2 s-1 is 2.17 times of its value at room condition and 6.67×10-4 s-1. Then, based on previous tensile results, the quantified comparisons of tensile and compressive mechanical properties under different experimental conditions were presented. Finally, a nonlinear constitutive model with damage was constructed to model the effect of pressure. The statistical damage model parameters were defined as ExpDec1 function of pressure P. The calibrated model can accurately predict the mechanical behaviour of the NEPE propellant under different confining pressure conditions and strain rates. [ABSTRACT FROM AUTHOR]