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In past seismic events, earthquakes have often caused significant damage to buildings. It is noteworthy that most of the existing buildings are reinforced concrete structures. Therefore, in order to mitigate the damage caused by earthquakes, it is important to conduct damage assessment of reinforced concrete structures. Considering that damage at the material level is the fundamental cause of component and structural performance degradation, indices based on material damage often have advantages in reflecting and evaluating component and structural damage. This paper proposes a damage constitutive model for concrete based on existing research results. Then, aiming at the shortcomings of current research on steel bar damage constitutive models, a steel bar damage constitutive model under cyclic loading is proposed, reflecting various failure modes of steel bars under seismic actions. Based on this, a multi-level damage index system from materials to components to structures is established. Through multi-level experimental simulations and finite element analysis, the accuracy of the proposed damage indices is validated, and performance indices for components and structures are provided. These indices can effectively reflect the damaged state of components and entire structures and can be used to guide seismic design, damage assessment, and strengthening design. [ABSTRACT FROM AUTHOR]

BACKGROUND: As a new intelligent polymer material, shape memory polymer (SMP) was a potential orthodontic appliance material. OBJECTIVE: This study aimed to investigate the thermodynamic responses of SMP under different loads via finite element analysis (FEA). METHODS: FEA specimens with a specification of 0.1 × 0.1 × 1 mm were designed. One end of the specimen was fixed, and the other was subjected to displacement load. Different loading, cooling, and heating rates were separately exerted on the specimen in its shape recovery process and used to observe the responses of the SMP constitutive model. Furthermore, specimens with various tensile elongation and sectional areas were simulated and used to elucidate their effect on shape recovering force. RESULTS: The specimens obtained a similar stress of 0.5, 0.44, and 1.07 Mpa for different loading, cooling, and heating rates after a long time. The shape recovering force of specimen increased from 0.0102 to 0.0315 N when the elongation improved from 10% to 40% and to 0.0408 N when the sectional areas were expanded to 0.2 × 0.2 mm. CONCLUSION: The stiffness of SMP was small at a high temperature but large at a low temperature. The effects of the loading, cooling, and heating rates on SMP can be eliminated after a long time. Furthermore, it was possible to increase the recovering force by increasing the elongation or expanding the sectional area of the specimen. The force was quadratically dependent on the elongation ratio. [ABSTRACT FROM AUTHOR]

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To minimize the impact on nearby structures during deep excavations, choosing an appropriate soil constitutive model for analysis holds significant importance. This study aims to conduct a comparative analysis of various constitutive soil models—namely, the Mohr–Coulomb (MC) model, the hardening soil (HS) model, the hardening soil small strain (HSS) model, and the soft soil (SS) model—to identify the most suitable model for the lacustrine deposit. To implement these models, the soil's index properties and mechanical behavior were evaluated from undisturbed soil samples. The numerical simulation and verification of these properties were carried out by comparing the laboratory test results with the outcome of the finite element method; the most suitable constitutive soil model for the soil was identified as the HSS model. Upon analyzing the wall deflection and ground settlement profiles obtained from respective constitutive models, it was observed that the HS and HSS models exhibit similar characteristics and are well-suited for analyzing typical lacustrine soil. In contrast, the MC and SS models yield overly optimistic results with lower wall deflection and ground settlement and fail to predict realistic soil behavior. As a result, this research highlights the significance of selecting the appropriate constitutive soil model and refining the parameters. This optimization process contributes significantly to the design of support systems, enhancing construction efficiency and ensuring overall safety in deep excavation projects. [ABSTRACT FROM AUTHOR]

A comprehensive hyperelastic model that precisely forecasts the mechanical characteristics of materials with rubber-like qualities is presented. This model relies on the well-established five-parameter Mooney-Rivlin model, which is then extended to incorporate strain rate dependent and temperature dependent term. To validate its accuracy, experimental data from ethylene propylene diene monomer (EPDM) rubber materials was utilized to compare with the model prediction. Hyperelastic stress-strain curves were collected from a variety of materials that were subjected to varying temperatures and strain rates to improve the model's applicability. Its prediction results are compared against the collected experimental data, resulting in consistent and reliable outcomes. The simplified form of the model not only establishes an effective framework for characterizing and predicting the mechanical response of materials that resemble rubber under different working conditions but makes the coding and implementation of finite element analysis easier. [ABSTRACT FROM AUTHOR]

It is difficult for the existing Burgers model to accurately depict the off-axis cyclic drawing process of woven coatings. In this paper, the mechanical deformation of woven PVC (polyvinyl chloride)-coated film at different temperatures is investigated. One-dimensional (1D) and two-dimensional (2D) constitutive models were established to characterize cyclic deformation processes. The 1D model is an improved Burgers model. The effects of the time dependence of the viscosity coefficient and the ratio of elastic to viscous deformation are considered simultaneously. The accuracy of the 1D model for predicting the cyclic nonlinear deformation at different temperatures and loading rates is improved. The 2D model is a nonlinear orthotropic model using polynomials. On the basis of the single-objective genetic algorithm, the inverse algorithm is used to obtain the shear polynomial coefficients in the tension phase and the shear modulus in the unloading phase, which circumvents performing the difficult shear test. UMAT subroutines of off-axis stretching and off-axis cyclic stretching are written separately. The intelligent inverse algorithm program consists of a single-objective genetic algorithm program, a finite element parametric modelling program, and a UMAT subroutine. The simulation results are compared with the off-axis cyclic tensile test data to validate the effectiveness and accuracy of the proposed 2D model for the analysis of the woven PVC-coated films in the tension–shear coupling state. [ABSTRACT FROM AUTHOR]

The increasing utilization of Fiber-Reinforced Concrete (FRC) within the construction industry signifies a pivotal shift towards enhancing structural integrity and durability. Despite the predominant use of steel fibers, exploring macro synthetic fibers has gained momentum due to their potential to address critical challenges, such as workability reduction and corrosion resistance in FRC, without markedly affecting its structural performance. Among the forefronts of FRC research is developing an accurate constitutive model encompassing the diverse behavior of fibers, particularly synthetic ones. This discrepancy necessitates a distinct constitutive model for synthetic fibers to precisely characterize their tensile postcracking behavior and regulate their design specifications. In this research, a preliminary constitutive model is derived through an inverse analysis procedure employing a Generalized Reduced Gradient (GRG) optimization method to the load-displacement results of the experimental testing of twenty ASTM C1609 beam samples. The results of the inverse analysis are used to correlate the ASTM C1609 residual flexural tensile strength parameters, fL/600 and fL/150 to the stress-strain points defining the uniaxial tensile curve of macro-synthetic fibers, achieving coefficients of determination exceeding 98.5%. The model is statistically confirmed to be a valid constitutive relation for macro-synthetic fibers via successfully representing the post-cracking load-deflection behavior of standardized concrete beams, thereby outperforming traditional constitutive models in simulating the post-cracking behavior of FRC. Moreover, the model demonstrates robust predictive capabilities for the load-deflection curve of externally standardized samples, showcasing its potential for broader application in FRC design and analysis. [ABSTRACT FROM AUTHOR]

For optimized design and better functioning of dental implants, researchers to a great extent have used the finite element method (FEM) as a computational/numerical tool. It appears from the review that, despite a significant amount of success in understanding the deformation and stress fields generated in dental implants and its surrounding bone, there are still several inadequacies prevailing in the constitutive models used in dentistry. Therefore, the theoretical/computational basis of dental prosthesis's deformation and stress analysis needs further improvement. To better understand the deformation and stresses produced in dental implants and their surrounding bone, the present work summarizes and discusses various constitutive models for titanium and its alloys as an implant material developed over the past few decades. The accomplishments and shortcomings of the current models are discussed. In addition, for completeness, the present study also summaries the effects of other factors in optimizing the dental implant. Critical findings indicate that longer dental implants effectively reduce stress gradients in the cortical peri-implant region. Threaded implants offer notable benefits, such as reduced bone stresses, enhanced osseointegration surface, and minimum slippage risk at the bone-implant junction. To further improve dental implant success rates, it is essential to consider the impact of dynamic loading and the viscoelastic behaviour of surrounding tissues. The use of porous implant structures shows promise in reducing maximum stress in cortical bone and enhancing load distribution, ultimately ameliorating the adverse effects of stress shielding in dental implant procedures. Further, some guidelines and research gaps have also been highlighted to develop more realistic time-dependent constitutive models of both implants and their surrounding bones. [ABSTRACT FROM AUTHOR]

With the advancement of numerical modeling, predicting tunnels' behavior before construction has become possible for designers. Accurate prediction of tunnels' behavior in diverse environments requires the compatibility of numerical simulations with ground conditions. Although several constitutive models have been proposed for simulating ground characteristics, their appropriate utilization is crucial. In this study, the convergence of a tunnel is modeled, and the results are verified using actual convergence monitoring data. Then, a series of finite element simulations are conducted on a hypothetical TBM tunnel to demonstrate the difference in deformations, ground surface settlements, and stresses in the lining resulting from tunnel excavation under seven constitutive models in rock media. The models are categorized into four groups: rock-specified, soil-established, and general. Additionally, parametric studies are performed on specific gravity, Poisson's ratio, and dilation angle. The findings revealed that different constitutive models significantly influence numerical analysis results. Rockspecified models were found to be more sensitive to parameter variation in rock media than soil-established and general models. Moreover, changes in specific gravity and Poisson's ratio had a significant impact on the magnitude of surface settlements. Overall, the study highlights the importance of appropriately selecting constitutive models and accurately defining material parameters in numerical simulations to ensure reliable predictions of tunnel behavior. [ABSTRACT FROM AUTHOR]

This article deals with the development of an elastic tetragonal model for the 2D auxetic rotating units structures in the framework of orthogonal transformations. The existing anisotropy in the structure was first determined by numerical simulations on the samples with different pattern orientation angles. A suitable representative volume element (RVE), which correctly represents the mechanical properties of the whole structure both in macroscale and in microscale, was then proposed by implementation of the kinematic periodic boundary conditions. In the next step, with the help of the orthogonal transformations relations, an anisotropic elastic model was developed, which correctly reflects the present tetragonal symmetry in the structure. Finally, the model parameters were identified and validated with the help of the corresponding experiments [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]

Eddy current dampers (ECDs) have emerged as highly desirable solutions for vibration control due to their exceptional damping performance and durability. However, the existing constitutive models present challenges to the widespread implementation of ECD technology, and there is limited availability of finite element analysis (FEA) software capable of accurately modeling the behavior of ECDs. This study addresses these issues by developing a new constitutive model that is both easily understandable and user-friendly for FEA software. By utilizing numerical results obtained from electromagnetic FEA, a novel power law constitutive model is proposed to capture the nonlinear behavior of ECDs. The effectiveness of the power law constitutive model is validated through mechanical property tests and numerical seismic analysis. Furthermore, a detailed description of the application process of the power law constitutive model in ANSYS FEA software is provided. To facilitate the preliminary design of ECDs, an analytical derivation of energy dissipation and parameter optimization for ECDs under harmonic motion is performed. The results demonstrate that the power law constitutive model serves as a viable alternative for conducting dynamic analysis using FEA and optimizing parameters for ECDs. [ABSTRACT FROM AUTHOR]

To calculate and analyze the equivalent resilient modulus of a submerged subgrade, a constitutive model considering the effect of saturation and matrix suction was introduced using ABAQUS's user-defined material (UMAT)subroutine. The pavement response under falling weight deflectometer (FWD) load was simulated at various water levels based on the derived distribution of the resilient modulus within the subgrade. The equivalent resilient modulus of the subgrade was then calculated using the equivalent iteration and weighted average methods. Based on this, the influence of the material and structural parameters of the subgrade was analyzed. The results indicate that the effect of water level rise on the tensile strain at the bottom of the asphalt layer and the compressive strain at the top of the subgrade is obvious, and its trend is similar to an exponential change. The equivalent resilient modulus of the subgrade basically decreases linearly with the rise in the water level, and there is high consistency between the equivalent iteration and weighted average methods. The saturated permeability coefficient and subgrade height have the most significant effect on the resilient modulus of the subgrade, which should be emphasized in the design of submerged subgrades, and the suggested values of the resilient modulus of the subgrade should be proposed according to the relevant construction conditions. [ABSTRACT FROM AUTHOR]

Owing to the challenge of capturing the dynamic behaviour of metal experimentally, high-precision numerical simulations have become essential for analysing dynamic characteristics. In this study, calculation accuracy was improved by analysing the impact of constitutive models using the finite element (FE) model, and the deep learning (DL) model was employed for result analysis. The results showed that FE simulations with these models effectively capture the elastic-plastic response, and the ZA model exhibits the highest accuracy, with a 26.0% accuracy improvement compared with other models at 502 m/s for Hugoniot elastic limit (HEL) stress. The different constitutive models offer diverse descriptions of stress during the elastic-plastic response because of temperature effects. Concurrently, the parameters related to the yield strength at quasi-static influence the propagation speed of elastic waves. Calculation show that the yield strength at quasi-static of 6061 Al adheres to y = ax + b for HEL stress. The R-squared (R2) and mean absolute error (MAE) values of the DL model for HEL stress predictions are 0.998 and 0.0062, respectively. This research provides a reference for selecting constitutive models for simulation under the same conditions. [ABSTRACT FROM AUTHOR]

Simple Summary: Traumatic brain injuries, a primary global health concern, can lead to severe disabilities. Acute subdural haematoma is one type of traumatic brain injury resulting from the rupture of bridging veins in the brain. Existing numerical models often oversimplify these structures. This study's main goals were to understand how the cerebral vein's cross-sectional shape affects its response, more akin to real-life testing, and to introduce a hyperelastic model for these veins that captures their non-linear behaviour. The results reveal that the vein's shape significantly influences its response to stretching, highlighting the need for more realistic geometries in modelling. Additionally, hyperelastic models, like the Marlow and polynomial models, were successfully implemented. This research provides valuable insights into the mechanical properties of bridging veins and their response to tensile loading, potentially improving our understanding of traumatic brain injuries. Traumatic brain injury (TBI) is a serious global health issue, leading to serious disabilities. One type of TBI is acute subdural haematoma (ASDH), which occurs when a bridging vein ruptures. Many numerical models of these structures, mainly based on the finite element method, have been developed. However, most rely on linear elasticity (without validation) and others on simplifications at the geometrical level. An example of the latter is the assumption of a regular cylinder with a constant radius, or the geometry of the vein acquired from medical images. Unfortunately, these do not replicate the real conditions of a mechanical tensile test. In this work, the main goal is to evaluate the influence of the vein's geometry in its mechanical behaviour under tensile loading, simulating the real conditions of experimental tests. The second goal is to implement a hyperelastic model of the bridging veins where it would be possible to observe its non-linear elastic behaviour. The results of the developed finite element models were compared to experimental data available in the literature and other models. It was possible to conclude that the geometry of the vein structure influences the tensile stress–strain curve, which means that flattened specimens should be modelled when validating constitutive models for bridging veins. Additionally, the implementation of hyperelastic material models has been verified, highlighting the potential application of the Marlow and reduced polynomial (of fourth and sixth orders) constitutive models. [ABSTRACT FROM AUTHOR]

This research paper focuses on evaluating the log piling technique as a sustainable, cost-effective, and environmentally friendly solution for reducing soil liquefaction risks during earthquakes. Although this method has been used extensively in Japan, mainly aiming for complete soil layer penetration, its economic viability is questionable in cases requiring very deep soil improvements. The study highlights that shallow ground improvement can notably enhance the seismic behavior of the soil-improvementstructure system, as evidenced by the reduced total and penetration settlements caused by liquefaction. The paper presents a methodology for determining the optimal dimensions of the modified ground zone using both small and medium-scale 1-g shaking table tests. The small-scale tests involve a detailed parametric study, examining variables like improvement width, pile spacing, and the depth-to-thickness ratio of the improved layer. Medium-scale tests, on the other hand, are geared towards identifying the minimum effective pile length. This approach provides a practical guideline for engineers to implement log piling for small residential buildings. Additionally, the paper utilizes finite element method (FEM) effective stress analysis, incorporating a PLAXIS 2Dbased constitutive model (PM4Sand) calibrated with laboratory undrained cyclic torsional tests. This model accounts for the changes in effective stress during seismic activities. Finally, the study correlates its numerical findings with the results from the 1-g shaking table experiments, offering a well-rounded perspective on the effectiveness of log piling in mitigating liquefaction risks during seismic events. [ABSTRACT FROM AUTHOR]

This paper presents a new anisotropic visco-hyperelastic constitutive model for finite bending of an incompressible rectangular elastomeric material. The proposed approach is based on the Mooney–Rivlin anisotropic strain energy function and non-linear visco-hyperelastic method. In this study, we aim to examine the mechanical response of a reinforced viscoelastic rectangular bar with a group of fibers under bending. Anisotropic materials are typically composed of one (or more) family of reinforcing fibers embedded within a soft matrix material. This operation may lead to an enhancement in the strength and stiffness of soft materials. In addition, a finite element simulation is carried out to validate the accuracy of the analytical solution. In this research, the well-known stress relaxation test, as well as the multi-step relaxation test, are examined both analytically and numerically. The results obtained from the analytical solution are found to be in good agreement with those from the finite element method. Therefore, it can be deduced that the proposed model is competent in describing the mechanical behavior of fiber-reinforced materials when subjected to finite bending deformations. [ABSTRACT FROM AUTHOR]

To develop a geological nuclear waste disposal facility from scratch, the hydro-mechanical properties of the host rock are fundamental for its initial construction, long-term system evolution, closure, and post-closure phases. In this paper, a transversely isotropic damage constitutive model was developed to describe the nonlinear behavior of clayey rock, based on the modified Drucker–Prager Cap model. Considering the self-sealing effect, a hydraulic conductivity evolution law of typical clayey rock was established based on in situ measurements. These theoretical models were further implemented in the finite element method software ABAQUS FEA (Finite Element Analysis) utilizing the subroutine USDFLD, which is a user subroutine to redefine field variables at a material point in ABAQUS. The hydro-mechanical response of an underground research laboratory during excavation and operation was reproduced by three-dimensional numerical simulation to validate the proposed models. The results highlighted that the developed theoretical model could efficiently reproduce the evolution of pore water pressure and deformation, compared to the in situ measurements in the excavation damaged/disturbed zone (EDZ) and hydraulic disturbed zone (HDZ) driven by tunnel excavation. Highlights: A damage constitutive model and a permeability evolution law are developed. Theoretical models are implemented in the software ABAQUS FEA. Hydro-mechanical responses of an underground research laboratory during excavation and operation are simulated. Comparison with the in-situ measurements highlights the theories' efficiency. [ABSTRACT FROM AUTHOR]

To address loading and unloading issues in civil and hydraulic engineering projects that employ coarse-grained soil as fill material under plane strain conditions during construction and operation, cyclic loading–unloading large-scale plane strain tests were conducted on two types of coarse-grained soils. The effects of coarse-grained soil properties on shear behavior and various modulus relationships were analyzed. The research results showed that coarse-grained soils with better particle roundness exhibit significant shear dilation deformation; it was also found that low parent rock strength can lead to strain softening, and an increase in confining pressure suppresses shear dilation deformation. During the cyclic loading–unloading process, the initial unloading modulus (Eiu) > unloading–reloading modulus (Eur) > initial reloading modulus (Eir) > initial tangent modulus (Ei), with the unloading modulus considerably greater than the others. In finite element simulations and model calculations, it is essential to select appropriate modulus parameters based on the stress conditions of the soil to ensure calculation accuracy. In this work, an elastoplastic and nonlinear elastic theory was used to establish a cyclic loading–unloading constitutive model. By comparing the values obtained using this model with experimental measurements, it was found that the model can reasonably predict stress–strain variations during cyclic loading–unloading of coarse-grained soils under plane strain conditions. [ABSTRACT FROM AUTHOR]

To solve the problem that twist springback of thin-walled component with asymmetric complex section cannot meet the high-precision quality requirement, FEA (finite element analysis) model of multi-pass roll forming (RF) process is established. Different material constitutive models are verified with RF tests, and the developed FEA model with variable elastic modulus and Yld2000 yield criterion is carried out to predict twist springback accurately. The mechanism of twist springback is studied by numerical simulations that twist springback results from the torque produced with the uneven residual longitudinal stress distribution due to the asymmetric forming for asymmetric section. The effect of different forming strategies on twist springback is discussed that developed UDT-type (USTB-Durable T) method with constant-arc-length method can effectively control twist springback. Orthogonal test is designed to study the effect of process parameters on twist springback. Results indicate that forming stands has the greatest impact on twist angle, followed by roll diameter and inter-distance, and roll gap has the smallest impact. The developed design and forming parameters are applied to control twist springback of asymmetric complex-section product. The actual product is deformed in industrial production line with the twist angle of less than 2 ∘ / m to meet high-precise quality requirement. [ABSTRACT FROM AUTHOR]

The clinch-adhesive joint has good mechanical properties and the curing degree of the adhesive during the clinching process shows significant impacts on the joint forming and its mechanical performance. During the clinching process, the interface of the cured adhesive layer restricts the flow of the metal thus shows a negative influence on the forming quality of the clinch-adhesive joint. This paper focuses on the interface layers change during the clinching process and the infulence of curing degree on the forming of clinch-adhesive joint by the finite element simulation model. Firstly, the constitutive model and interfacial failure criterion of Araldite 2015 epoxy adhesive considering curing degree were fitted through tensile tests for adhesive dumbbell specimens and bonding joints. Then, the forming process of the clinch-adhesive joints with fully cured adhesive were simulated. Finally, the effects of curing degree on the joint shape and interface failure were investigated. The results show that interface damage occurs at the location of the self-locking, and the curing degree mainly shows influences on the sizes of adhesive pocket and undercut, the damaged width of the interface layers, and the maximum damage of the interface layers. [ABSTRACT FROM AUTHOR]

This study proposes a macroscopic finite element modelling and simulation approach considering the temperature dependency of both in-plane membrane and out-of-plane bending behaviours. This approach enables the investigation of the effect of the deformation mechanisms on the quality of the formed thermoplastic composite parts during the thermo-forming process. The temperature-dependent constitutive model of the in-plane tensional behaviour is considered linear, whereas the in-plane shear stiffness is modelled based on the nonlinear hypoelastic constitutive equation. The out-of-plane bending behaviour is considered by decoupling the membrane and bending method. A numerical simulation strategy is developed by implementing the ABAQUS software via a VUMAT subroutine. Moreover, a modified method is introduced for the qualitative and quantitative assessment of the wrinkling intensity generated in the forming process. The validated strategy is used to investigate the influences of the various temperature conditions of the forming process and the underlying mechanisms to optimise the thermo-stamping process. [ABSTRACT FROM AUTHOR]

The traditional homogeneous JC constitutive model can be used to perform the simulation of the mechanical properties effectively during the cutting process. However, polycrystalline material properties are not considered, and the effect of grain boundaries on the cutting process is ignored. In order to study the effect of grain boundary on micro-deformation during the cutting process of Inconel718, the grain size through the EBSD experiment was obtained firstly. A finite element simulation model of dynamic cutting of 2D polycrystal with grain boundaries was established using Python language and MATLAB software. A new material constitutive model with grain boundary effect is established by introducing the JC model into the geometrically necessary dislocation (GNDs) theory. By writing a VUMAT subroutine to achieve secondary development of ABAQUS, the established constitutive model is used for cutting simulation. Through the comparison of experimental results and simulation results, the model can accurately reflect the changes in cutting force, cutting temperature, and equivalent stress. On this basis, the influence of temperature on geometrically necessary dislocations, the influence of grain boundaries on the evolution of chip morphology, and the initiation and propagation of cracks are further analyzed. [ABSTRACT FROM AUTHOR]

The adequate interfacial pressure of silicone rubber in cable intermediate joints is a basic condition to ensure the normal operation of cable joints, while high temperature and ageing in the operation of actual cables and accessories would affect the magnitude of interfacial pressure. The uniaxial tensile force of two different silicone rubbers for 10 kV cold-shrink joints at different temperatures and thermal ageing times was measured by experiment, and the Yeoh rubber intrinsic structure model was fitted according to the measured data. The material model was embedded into a two-dimensional axisymmetric finite element simulation model of the structure, and the relationship between the interference, temperature, thermal ageing time and interfacial pressure was investigated. The results show that the interfacial pressure increases linearly with the increase in interference. At the same interference, the interfacial pressure at the root of insulating silicone rubber and semiconducting silicone rubber increased by 9.1%, 12.3%, 6.4% and 9.2%, 16.3%, 5.6%, respectively, at 50, 75, and 100 °C compared with room temperature, and the largest interfacial pressure of cable joints was at 75 °C. Using the established ageing life prediction model based on the Arrhenius principle, the service life of the accessories was predicted to be 28.9 years at 90 °C of operating temperature and interfacial pressure greater than 55% of initial interfacial pressure. [ABSTRACT FROM AUTHOR]

Ground movements induced by deep excavations may cause damages on neighboring existing buildings. Finite element simulations generally give acceptable estimates of the horizontal displacements of the retaining wall, but results are less satisfactory for the vertical displacements of the ground surface behind the structure. A possible explanation is that most constitutive models describe volumetric strains in a simplified way. This paper proposes an elastoplastic constitutive model aimed at improving the prediction of vertical displacements behind retaining walls. The model comprises a single plastic mechanism with isotropic strain hardening, but has a specific flow rule that allows to generate contractive plastic strains. Identification of the parameters based on triaxial tests is explained and illustrated by an example of calibration. A numerical analysis of a well-documented sheet pile wall in sand in Hochstetten (Germany) is presented. The results given by the model are compared with the measurements and with those obtained using the Hardening Soil Model. The potential advantages of the proposed model are then discussed. [ABSTRACT FROM AUTHOR]

The finite-depth concrete panels have been widely applied in the protective structures, and its impact resistance and dynamic fracture failures, especially the scabbing/perforation limits, under high velocity projectile impact, are mainly concerned by protective engineers, which are numerically studied based on an improved dynamic concrete model in this study. Firstly, based on the framework of the KCC (Karagozian & Case concrete) model, a dynamic concrete model is proposed which considers an independent tensile damage model and a continued transition between dynamic tensile and compressive properties. Secondly, the strength surface, equation of state and damage parameters of the proposed model are comprehensively calibrated by a triaxial compressive test with high confinement pressure, the rationality of which is further verified based on the single element tests, e.g., uniaxial and triaxial compression as well as uniaxial, biaxial and triaxial tension. Thirdly, a series of projectile high velocity impact tests on thin and thick concrete panels are simulated, which indicates that the projectile residual velocity and dynamic fracture failures are reproduced satisfactorily, while the KCC model underestimates both the spalling and scabbing dimensions severely. Finally, based on the validated concrete model and finite element analyses approach, the validations of the existing five empirical formulae are evaluated, in terms of the depth of penetration (DOP) and scabbing/perforation limits of concrete panel. Both the Army corps of engineers (ACE) and modified National Defense Research Committee (NDRC) formulae are recommended in the design of the protective structure to avoid scabbing failure. [ABSTRACT FROM AUTHOR]

Solder joints are generally the weakest part in electronic packaging structure whose fatigue life depends to a large extent on the durability of solder joints. In pursuit of a balance between environmental protection and soldering performance, commonly used Sn–Pb solder should be modified by adding other chemical elements to reduce Pb content. This work aims to investigate the performance of different solder materials and explore the impact of different electronic package structures. Firstly, tensile experiments are performed on three kinds of solders (Sn–Pb, Sn–Pb–In, Sn–Pb–Bi) to obtain their mechanical behavior, and then the constitutive laws of them are calibrated by Anand model. Additionally, finite element method (FEM) is used simulate the response of plastic ball grid array (PBGA) package structure under thermal cycles, and mechanical variables including deformation, equivalent stress, and equivalent strain are analyzed. Finally, Coffin-Manson and Engelmaier equations are adopted to predict the fatigue life of package structures and the effects of various factors such as solder materials, dimensions of components, and welding quality are further investigated. Results reveal that adding Bi into Sn–Pb solder can make the solder joints have better performance. From the perspective of optimum fatigue life, the plastic package thickness is recommended in the range of 0.8 mm–0.9 mm, the chip thickness is recommended as 0.35 mm, the substrate thickness is recommended to be less than 0.34 mm, and the ratio of stand-off height to solder ball diameter should be controlled between 0.6 and 0.7. According to the prediction, the solder ball diameter is suggested to be 0.54 mm so that fatigue life could reach 194 cycles, and the stand-off height for this package structure is suggested to be 0.36 mm so that fatigue life could reach 123 cycles. [ABSTRACT FROM AUTHOR]

Shape memory hydrogel is a type of hydrogel whose shape can transform between a temporary shape and its initial shape when exposed to external stimuli, such as water, temperature, and pH. Over the last decade, shape memory hydrogels have gained increasing interest owing to their distinct properties; however, constitutive models to describe their shape memory mechanism are still lacking. In this paper, we propose a constitutive model for water-triggered shape memory hydrogels based on the transition between the sparse and dense phases. In the model, the shape memory process is identified using two internal variables: the frozen deformation gradient and dense phase volume fraction. To validate the model for describing shape memory effects, we implemented the model in the finite element method using a user-defined element (UEL) subroutine in ABAQUS. To verify the accuracy of the proposed UEL, we simulated the water-triggered shape memory effects in different recovery processes under different uniaxial loads. Furthermore, we investigated the water-triggered shape memory behavior of a self-bending bilayer structure and a four-arm gripper structure using both experiments and simulations. Good agreement was observed between the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Argillaceous rocks are candidate host and/or cap formations for the geological disposal of nuclear wastes in many countries, including Canada, France and Switzerland. The understanding of the long term mechanical behaviour of such rocks is an essential requirement for the assessment of their performance as a barrier against radionuclide migration. Due to the existence of bedding, argillaceous rocks are inherently anisotropic and the development of stress-strain models for their mechanical behaviour needs to take this anisotropy into account. This paper presents two examples of the practical implementation of stress-strain relationships in finite element models to simulate the excavation damage zones (EDZ) in bedded argillaceous rocks. The first example concerns the EDZ around a micro-tunnel in Opalinus Clay, in Switzerland. The second example relates to the EDZ around the century-old tunnel in Tournemire shale, in France. Both examples show the importance of developing robust stress-strain models that can replicate inherent anisotropy of the rock, and of calibrating and validating the models with a comprehensive set of laboratory experiments. The second example shows the additional influence of dessication and fault zone on the extent and shape of the EDZ. [ABSTRACT FROM AUTHOR]

In this study, cyclic tension tests were conducted on ordinary Galfan cables and locked coil Galfan cables with diameters of 40 mm to evaluate their mechanical properties under cyclic tension. The mechanical behavior of the two kinds of Galfan cables under monotonic loading and cyclic tension was analyzed, while the differences in strength and the mechanical properties of the two kinds of Galfan cables and the effects of different loading systems on the mechanical properties of the two kinds of cables were obtained. The Ramberg–Osgood model was used to fit the skeleton curve. The elastic and inelastic behaviors during loading and unloading were studied. The change in elastic modulus of the Galfan cable with respect to cyclic load is proposed, and the exponential model of strain and elastic modulus under cyclic load is established, which lays a foundation for the accurate finite element analysis of cable structure response under strong earthquake and other accidental loads. [ABSTRACT FROM AUTHOR]

The present study aims to formulate a new multiscale constitutive model of human trabecular bone. The trabecular bone was modelled as a nonlinear viscoelastic material. The viscoelastic effects of single trabeculae were considered by means of a hereditary integral in which stress depends on time and strain, while the elastic response was described by the hyperelastic Mooney–Rivlin model. The cuboid bone sample was extracted from the femoral head during the hip replacement surgery. The material constants in the constitutive equation were identified based on the stress relaxation test performed on the cuboid sample and the microindentation tests performed on trabeculae using the curve-fitting procedure. The microindentation tests were performed using a spherical tip instead of Vickers or Berkovich tip to minimize plastic effects during trabecular deformation. In order to validate formulated constitutive model, results from a FE simulation of stress relaxation test and uniaxial compression test were compared to the results of the corresponding experiments conducted on a macroscopic bone sample. Good agreement was observed between numerical and experimental results. The viscoelastic behaviour predicted by the proposed constitutive equation corresponds well to the response of human trabecular bone under various types of load conditions. This demonstrates the high ability of our constitutive model to simulate the behaviour of trabecular bone on a micro- and macroscopic scale. Thus, we conclude that the model, which was formulated for a single trabecula, can be successfully applied to simulate mechanical behaviour of the tissue in a macroscale. [ABSTRACT FROM AUTHOR]

BACKGROUND AND OBJECTIVES: Harmful ruptures and instabilities in landfills in recent years have highlighted the importance of studying the municipal solid waste and its behavior. These instabilities mostly occur in the landfill of developing countries where waste materials are degradable and saturated. The behavior of waste and its ingredients are unknown as the main reasons for such instability. The main goal of this study was to better predict the behavior of landfills and unknown materials in municipal solid waste to prevent the environmental disasters. METHODS: A cylindrical specimen was modeled and subjected to triaxial test loading conditions using the finite element method. Also, fresh waste, as a waste sample with a specific composition, was investigated. Using the optimization method, the constants of the presented equation were obtained and the basic model of stress strain was presented based on composite theory. FINDINGS: The whole models for predicting the waste behavior were presented based on the behavior models of soils. This was carried out by the theory of composite materials, which was used for the first time in this study. At the strains of less than 30 percent, a well agreement was observed between the results of the numerical and the present methods. Also, at confining stresses less than 100 kiloPascal, the root mean square of the relative error percentages between the total stresses obtained from the present model and another model was less than 10 percent. At higher confining stresses, this amount was in the range of 10 - 20 percent. CONCLUSION: The results of this study were compared with those of the experimental data in previous models to verify the proposed model. The model proved to be capable of simulating and predicting the municipal solid waste behavior under various loading conditions efficiently. The results implied that assuming the municipal solid waste as composite material was reasonable and could be extended to future studies. [ABSTRACT FROM AUTHOR]

• Fractional gradient direction replaces additional plastic potential. • The FEM implementation of the fractional elastoplastic constitutive model is presented. • The influence of the fractional order on the strain localization is investigated. • Examples are analyzed to demonstrate the effectiveness of the implementation process. The plastic strain localization phenomenon is of critical importance for rock-like materials when undergoing non-homogeneous deformation. This paper presents a fractional plastic framework which is applied to take into account the plastic strain localization of rock-like materials. The novelty of the presented framework lies in the non-coaxial plastic flow that is controlled by the RiemannLiouville (RL) fractional derivative without additional plastic potential. The hardening response is described by a function of the generalized plastic shear strain. The capability of the fractional constitutive model to predict the main mechanical behaviors of rock-like materials is assessed by the conventional triaxial compression test data of Vosges sandstones from the literature. With the help of a MATLAB-based finite element method, several numerical examples (i.e., a plate, a plate with a hole, and a plate with a crack) are implemented, compared and analyzed to demonstrate the effectiveness of the proposed framework and the influence of the fractional order on the strain localization. It can be found from the numerical application of the twin-tunnel that the fractional model is promising to flexibly capture the strain localization zone for rock-like materials. [ABSTRACT FROM AUTHOR]

The stability of deep excavation is often investigated through numerical simulation. However, most constitutive models cannot take into account the influence of disturbance on soil response, especially for excavations in sandy soils. In this study, the conventional Duncan-hang constitutive model is modified based on the data obtained from a series of triaxial consolidated drained tests on medium coarse sand with different relative densities, where all input parameters in the model are correlated with the changes in relative density due to disturbance. The modified hyperbolic model is then implemented in the general-purpose finite element code, ABAQUS. The efficiency of the proposed constitutive mode is demonstrated by comparing with the experimental data. Furthermore, a case study of a largescale propped excavation for a subway station in Shenyang is analyzed through numerical calculations with the conventional Mohr-Coulomb model and the proposed hyperbolic model, and theoretical derivations based on the current technical code in China. It is found that the proposed approach can provide reasonable estimations compared with field measurements with a maximum error of 28% for maximum horizontal displacement of the solider pile and of 8% for maximum ground surface settlement, whereas the other techniques overestimate the behaviour of deep excavation significantly by more than 90%. [ABSTRACT FROM AUTHOR]

The longitudinal compressive properties and stress–strain relationship of original bamboo at different culm heights were studied by a uniaxial compression experiment. The experimental results show that the failure mode of bamboo is bulging failure, and its ultimate compressive strength increases linearly with the increase of height at the bamboo culm. The longitudinal compressive stress–strain curves of bamboo at different heights are normalized, and the three-stage nonlinear constitutive model and the Boltzmann constitutive model are established. The two models are close to the experimental results and can describe the main stages of bamboo compression. A finite element model of the compression specimen is established to verify the accuracy of the proposed constitutive model, and bamboo column models with different slenderness ratios are established to evaluate the feasibility of the proposed constitutive model in buckling analysis. The results show that the finite element model can well simulate the buckling capacity of the bamboo column after introducing the initial defect of L/500, while the slenderness ratio is greater than 30. This work is expected to be useful for the finite element analysis of bamboo and prediction of buckling capacity of original bamboo columns. [ABSTRACT FROM AUTHOR]

This paper presents a two-phase composite model for predicting the shape memory and recovery behaviors of polymeric and particle-loaded polymeric composite parts. The shape recovery behavior is simulated using a homogenized material model with the matrix exhibiting the strain storage behavior and the inclusions adding to the stiffness and conductivity of the material. An electrically conductive reinforcement in the matrix enabled the activation of shape recovery with Joule heating. The shape recovery model for the matrix is adapted from literature and extended to include a three-dimensional stress state. Inclusions are assumed linearly elastic, and the matrix is elastic at the low-temperature glassy phase and elastic-incompressible at the high-temperature rubbery phase. The incompressibility is modeled using a temperature-dependent Poisson's ratio that approaches close to 0.5 for the rubbery phase. A methodology for characterizing model parameters from experimental observations of shape recovery is also discussed. Correlations with experimental observations calibrate the model as well as validate it. The formulated two-phase shape recovery model was implemented into the 3D nonlinear finite element analysis. Simulations of shape recovery arbitrarily shaped 3D parts under multi-axial stress states and thermo-mechanical loading cycles are described. [ABSTRACT FROM AUTHOR]

The rapid spread of the finite element method has caused that it has become, among other methods, the standard tool for pre-clinical estimates of bone properties. This paper presents an application of this method for the calculation and prediction of strain and stress fields in the femoral head. The aim of the work is to study the influence of the considered anisotropy and heterogeneity of the modeled bone on the mechanical fields during a typical gait cycle. Three material models were tested with different properties of porous bone carried out in literature: a homogeneous isotropic model, a heterogeneous isotropic model, and a heterogeneous anisotropic model. In three cases studied, the elastic properties of the bone were determined basing on the Zysset-Curnier approach. The tensor of elastic constants defining the local properties of porous bone is correlated with a local porosity and a second order fabric tensor describing the bone microstructure. In the calculations, a model of the femoral head generated from high-resolution tomographic scans was used. Experimental data were drawn from publicly available database "Osteoporotic Virtual Physiological Human Project." To realistically reflect the load on the femoral head, main muscles were considered, and their contraction forces were determined based on inverse kinematics. For this purpose, the results from OpenSim packet were used. The simulations demonstrated that differences between the results predicted by these material models are significant. Only the anisotropic model allowed for the plausible distribution of stresses along the main trabecular groups. The outcomes also showed that the precise evaluation of the mechanical fields is critical in the context of bone tissue remodeling under mechanical stimulations. [ABSTRACT FROM AUTHOR]

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The harvesting of green Sichuan pepper (Zanthoxylum armatum) is achieved by cutting the branches, and it is important to investigate the biomechanical properties of the branches for harvesting. In this study, based on the elastic mechanics of composite materials, the Yamada and Sun yield strength criterion, hardening model, and flow law were selected, and a damage factor was introduced to establish the constitutive model of green Sichuan pepper branches. This model can characterise the complex biomechanical properties of green Sichuan pepper branches, which provides a new way and saves time for green Sichuan pepper branch testing, and lays a theoretical foundation for the design and optimisation of green Sichuan pepper production machinery. Furthermore, the constitutive parameters of the green Sichuan pepper branches were measured for the first time to meet the needs of the established model. In addition, an effective bending indenter-branch finite element model was established by compiling the constitutive model into the simulation software Abaqus through the Umat subroutine, and a three-point bending simulation test was conducted on the branch of green Sichuan pepper. Finally, relative deviation from maximum pressure founded to be less than 6% by comparing the experimental results with the simulation, which proved that the model was reliable and the measured constitutive parameters were accurate. Looking forward, these findings may contribute to the development of green Sichuan pepper harvesting equipment worldwide. • A simulation model of the mechanical properties of green Sichuan pepper branches. • Systematic determination of the mechanical parameters of green Sichuan pepper branches. • Analysis of green Sichuan pepper branches using numerical simulation. • Advantages of using models and parameters for multi-case simulations. [ABSTRACT FROM AUTHOR]

A damage-coupled plastic-stress-state (DCPSS) constitutive model was developed to address the effect of proportional and non-proportional loading paths on the plasticity and failure of ductile metals. This constitutive model was calibrated using the load–displacement curves of 11 shapes of aluminum alloy specimens by Finite Element Assisted Methods. The trial-and-error method, genetic algorithm-based optimization, a combined experimental/numerical method, and Fischer's integral extension were applied to determine the material constants in the constitutive model. The determined model can accurately predict the flow behavior and failure processes of AA5754-H32 aluminum under proportional loading conditions, such as crack initiation, propagation, and fracture. The accuracy of DCPSS model is validated by using uniaxial pretension-shear test and biaxial pretension-shear test, which shows to be significant. [ABSTRACT FROM AUTHOR]

The non-unique critical state represents the distance between the critical state line (CSL) and the isotropic consolidation line (ICL) that significantly varies with stress paths and particle size distribution of soils. A structural bounding surface plasticity model with spacing ratio r (SBSP-R model) was implemented using an explicit algorithm. However, the explicit algorithm did not well capture the non-unique critical state of soils with a large spacing ratio r, which prevented the soil mechanics research on non-unique critical state via finite element analysis. To overcome the limitation, the implicit algorithm of the SBSP-R model is formulated, and it mainly includes elastic prediction and plastic correction. The plastic correction is realized using the Newton–Simpson scheme with a controlling equation set related to consistency condition, plastic flow, hardening parameter, structural bounding surface, plastic modulus, and mapping rule. Case studies indicate that the implicit algorithm of the SBSP-R model is right and stable in predicting non-unique critical states. Comparisons between predicted and tested results indicate that the implicit algorithm of the SBSP-R model not only captures the critical state, stress-strain, and stress paths of various soils but also shows higher computational accuracy and efficiency compared with the previous explicit algorithm. These results indicate that the formulated implicit algorithm of the SBSP-R model is an alternative approach to the previous explicit algorithm. [ABSTRACT FROM AUTHOR]

An understanding of the creep behavior of clayey rocks is considered fundamental for further development in the fields of nuclear waste underground disposal, underground mine design, strata control, and many other geological phenomena occurring in the earth's crust. In this research, we performed a series of long-term triaxial compressive tests on a typical clayey rock, which confirmed its high creep potential beyond the creep threshold. Further analysis of the creep mechanism of this clayey rock indicated that two effects—strengthening and damage—are accompanied by the creep process. Additionally, based on the overstress theory and Drucker–Prager cap model, we developed a novel constitutive model considering two creep reference surfaces—cohesion and consolidation. Meanwhile, laws to reflect the strength and damage effect during creep were established and applied to the above constitutive model. Finally, the above theoretical studies were implemented in the finite element method software ABAQUS FEA using the subroutines CREEP and USDFLD. Some theory parameters were verified through back analysis. A comparison between the experimental results and numerical simulations confirmed the superiority of the established theoretical model. Highlights: Clayey rock exhibits high creep potential beyond the creep threshold. Two effects—strengthening and damage—are accompanied by the creep process. A novel creep constitutive model was established. Strengthening and damage laws during creep were developed. Model numerical implementation and parameters determination. [ABSTRACT FROM AUTHOR]

The stability of cement sheath under high temperature and high pressure is one of the most critical issues for the durability of geothermal well systems. In this study, a two-dimensional plane-strain finite element code was developed to investigate the coupled thermomechanical behaviors of the casing-cement-formation system. Different from previous linear elastic analyses, a thermoelasto-plastic constitutive model based on the thermodynamic theory was adopted for the cement sheath. It is shown that the finite element simulations using the proposed model provide a more accurate and realistic prediction of stress--strain responses of the cement sheath under high temperature. The results demonstrate that the radial stress concentration and the tensile strain concentration occur at both the cement--casing interface and the cement--formation interface, where the cement sheath is most likely to fail. High strength and low stiff- ness in the cement sheath and the formation are preferred for the integrity of the system. Both large thermal cycles and large differences between the internal fluid pressure and the external pressure should be avoided during operation. The new code is an alternative tool for guiding the geothermal well design. The finite element framework described herein is universal for other thermo-mechanical applications, such as energy foundations and energy tunnels. [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]

Two failure modes of laminated glass under impact loading are summarized, after which a series of experiments are carried out and a three-stage breakage model for laminated glass plate is proposed. The three-stage breakage model consists of an elastic stage (stage Ⅰ), a stage of total breakage of the back glass layer (stage Ⅱ) and a stage of total breakage of both layers of glass (stage Ⅲ). Furthermore, a combined TCK-JH2 constitutive model is proposed for the numerical analysis conducted with Finite Element Method (FEM). In this constitutive model, the TCK model is employed when the material is under tensile condition whereas the JH2 model is employed when the material is under compressive condition. Moreover, a stiffness recovery behavior is defined. The criterion of tension and compression is studied as well. [ABSTRACT FROM AUTHOR]

Forming large thin-walled hemispherical parts by hydroforming, serious thinning of wall thickness, instability of suspension area, and fracture are often accompanied. In order to solve the above problems, this paper takes AA6061-T6 aluminum alloy thin-walled hemispherical parts as the research object, and uses the method of finite element numerical simulation analysis and experimental verification to carry out the formability analysis of double-layer sheet hydroforming. In order to improve the accuracy of numerical simulation, uniaxial tensile tests are carried out on AA6061-T6 tensile specimens. Based on the BP neural network prediction model, a constitutive model that can truly reflect the plastic deformation characteristics of materials is established, which can provide more accurate material properties for numerical simulation. In this paper, the wall thickness and fittability of the parts are taken as the evaluation indexes, and the simulation analysis of the double-layer sheet hydroforming is carried out combined with the pre-bulging process, and the process flow of the single-sheet and the double-layer sheet hydroforming is compared and analyzed. The forming law of formed sheet under different friction coefficient between sheets and different upper sheet thickness is discussed. In addition, the influence of different temperature on the forming quality of parts is also discussed. It is found that the sheet metal will soften at the appropriate temperature, and the wall thickness distribution of the parts suspending area will be further improved. Finally, the forming experiments are carried out using the optimized process conditions, and the results are basically consistent with the simulation results. The results show that the research can effectively provide scientific guidance for the forming of large thin-walled hemispherical parts. [ABSTRACT FROM AUTHOR]

Purpose: The stress–strain behaviors of rockfill materials in dams are significantly affected by the anisotropy and grain crushing. However, these factors are rarely considered in numerical simulations of high rockfill dams. This study intends to develop a reasonable and practical constitutive model for rockfill materials to overcome the above problems. Design/methodology/approach: The effects of anisotropy and grain crushing are comprehensively considered by the spatial position of the reference state line. After the improved generalized plasticity model for rockfill materials (referred to as the PZR model) is developed and verified by laboratory tests, it is used with the finite element method to simulate the stress–strain behaviors of the Nuozhadu high core rockfill dam. Findings: The simulated results agree well with the laboratory tests data and the situ monitoring data, verifying the reliability and practicability of the developed PZR model. Originality/value: A new anisotropic state parameter is proposed to reflect the nonmonotonic variation in the strength as the major principal stress direction angle varies. This advantage is verified by the simulation of a set of conventional triaxial tests with different inclination angles of the compaction plane. 2) This is the first time that the elastoplastic model is verified by the situ monitoring data of high core rockfill dams. The numerical simulation results show that the PZR model can well reflect the stress–strain characteristics of rockfill materials in high core rockfill dams and is better than the traditional EB model. [ABSTRACT FROM AUTHOR]

The surface deformation behind deep excavation support in sand soil was validated. Furthermore, the displacement of ground surface and invert of buried circular tunnel (diameter D = 6 m) induced by deep excavation in layered soft soil was evaluated. The validation was performed for the results of centrifuge models of sand soil by applying Mohr-Coulomb model (MC) in 2D finite element analysis. In addition, the evaluation was conducted for the MC model by applying Hardening Soil with Small Strain Stiffness (HSS) on a model in soft soils. Beginning an excavation in soft soils causes drawdown stresses that causing an abrupt increase in tunnel movement (strain dependent stiffness). MC model cannot adopt the effect of excavation increase on the surface of soft soil and on the invert of tunnel (under-predicted deformation). HSS adopts a steep drawdown for soft soil surface above the tunnel and indicates a marked decrease in the heave of tunnel invert (over-predicted deformation). According to the deformation of sand surface behind diaphragm wall of excavation, an accepted convergence was observed between the centrifuge sand tests and 2D numerical analysis. [ABSTRACT FROM AUTHOR]

The purpose of this study is to obtain the digital twin parameters of the thyroid gland and to build a constitutional model of the thyroid gland based on continuum mechanics, which will lay the foundation for the establishment of a surgical training system for the thyroid surgery robot and the development of the digital twin of the thyroid gland. First, thyroid parenchyma was obtained from fresh porcine thyroid tissue and subjected to quasi-static unconfined uniaxial compression tests using a biomechanical test platform with two strain rates (0.005 s−1 and 0.05 s−1) and two loading orientations (perpendicular to the thyroid surface and parallel to the thyroid surface). Based on this, a tensile thyroid model was established to simulate the stretching process by using the finite element method. The thyroid stretching test was carried out under the same parameters to verify the validity of the hyperelastic constitutive model. The quasi-static mechanical property parameters of the thyroid tissue were obtained by a quasi-static unconstrained uniaxial compression test, and a constitutional model that can describe the quasi-static mechanical properties of thyroid tissue was proposed based on the principle of continuum media mechanics, which is of great value for the establishment of a surgical training system for the head and neck surgery robot and for the development of the thyroid digital twin. [ABSTRACT FROM AUTHOR]

The increasing embrace of the low-carbon and environmentally sustainable construction approach has opened exciting opportunities for using environmentally friendly geopolymer based ultra-high-performance concrete (G-UHPC) in engineering structures, drawing significant attention to its performance. Seismic performance is a crucial factor in structural design, and it is greatly affected by the bond behavior between steel bar and concrete. As a result, a thorough understanding of the bond behavior of steel bars to G-UHPC provides essentially theoretical support for the structural design and nonlinear finite element analysis of G-UHPC structures, which is vital for their widespread implementation in earthquake engineering. This study tested 54 specimens from 18 groups to examine the bond performance of G-UHPC and steel bars under cyclic loading. The influence of concrete and steel bar types, protective layer thickness, bond length, and steel fiber on critical bond performance indicators were evaluated, and the bond stress-slip hysteretic and skeleton curves were analyzed. Subsequently, based on the experimental data, a constitutive model was proposed to predict the bond stress-slip relationship of steel bars and G-UHPC under cyclic loading. The results indicated that the steel bars exhibited superior bond performance with G-UHPC as compared to NSC. The bond and residual strength between steel rebars and G-UHPC was approximately 1.73 times and 3 times greater, respectively, in comparison with that between NSC and steel rebars. Increasing the strength of steel bars only resulted in a limited 2 % improvement in bond strength. The steel bar diameter, protective layer thickness, bond length, and the dosage and length of steel fibers in G-UHPC significantly influenced the bond performance. The addition of irregular-shaped steel fibers to G-UHPC has demonstrated potential in improving energy consumption, with the most remarkable enhancement observed for the inclusion of twisted steel fibers. Specifically, the incorporation of twisted steel fibers signally enhanced the energy consumption to approximately 1.3 times the energy dissipation as compared to straight steel fibers with the same dosage and aspect ratio. In addition, the accuracy of the proposed constitutive model has been validated. • The bond of G-UHPC and steel bars under cyclic loading was investigated. • The influences of different factors on bond performance were examined. • The bond stress-slip hysteretic curves and skeleton curves were analyzed in detail. • A constitutive model for predicting the bond stress-slip relationship was proposed. [ABSTRACT FROM AUTHOR]