Elastic-plastic Constitutive Model Research Articles

Thermo-Hydro-Mechanical Numerical Analysis of Energy Pile in Saturated Clay

In order to study the mechanical properties of energy piles under long-term heat injection-heat extraction cycle loading conditions, the influence of temperature on the mechanical properties of foundation soils needs to be considered. The subroutine of an elastic-plastic constitutive model of soil considering the influence of temperature is developed in Abaqus. Finally, the changes of additional pile top displacement, lateral friction resistance and axial force of energy pile under long-term heat injection-pumping cyclic loading under different loads and different soil parameters under the same load are discussed. The results show that: (1) The soil around the pile is subjected to plastic deformation due to the expansion and contraction of the pile. The higher the load on the pile top is, the greater the additional temperature settlement generated at the pile top is. (2) Under 0.5PU load, the increase of OCR, swelling index or permeability coefficient of foundation soil will cause the decrease of additional settlement of pile top. And the additional side friction and axial force, plastic parameters or soil permeability coefficient increases will produce greater additional side friction and axial force. This study has certain significance for the long-term use of energy piles.

Overview of the Constitutive Model and Numerical Calibration by FEM to Compute Bearing Capacity and Embankment-Core Deformability

Numerical modeling is a powerful tool to determine the stress-strain relationships of structures. However, for a reliable application, physical and mathematical models must be calibrated and validated. This paper presents an overview of numerical calibration through the finite element method and plate-load tests in an embankment. Additionally, an analysis of the constitutive models used in soils is performed, and the elastic-plastic constitutive model of Mohr-Coulomb was selected since it is the best suited for this study. The results from three test areas within a refinery project that the Cuban government undertook in the province of Cienfuegos are used. The numerical model used in this study was calibrated by means of the error theory and the non-parametric hypothesis tests from Mann-Whitney U. From the practical point of view, this study gives two procedures to calibrate the numerical model with experimental results.

A finite deformation multiplicative plasticity model with non–local hardening for bonded geomaterials

The paper presents a finite deformation, isotropic hardening, non–associative elastic–plastic constitutive model (FD_Milan model) for describing the mechanical behavior of a wide range of bonded natural geomaterials such as stiff overconsonsolidated clays, porous soft rocks or bio–improved soils. The formulation of the model is based on the multiplicative split of the deformation gradient and on the assumption of hyperelastic behavior. To deal with the occurrence of strain localization, typically observed in this class of geomaterials, the model has been equipped with a non–local version of the hardening laws. This approach is capable of regularizing the pathological mesh dependence occurring in the post–localization regime when adopting classical plasticity models.In view of its application to practical geotechnical problems characterized by large displacements and deformations within a hydro-mechanical coupled environment, the model has been implemented in the recently developed Particle Finite Element code G–PFEM for geomechanics applications.To demonstrate the effectiveness of the numerical implementation, a series of numerical simulations has been performed considering two representative boundary value problems: the modeling of shear localization in plane strain biaxial tests and the simulation of CPTu tests in a saturated porous soil. The results of biaxial test simulations have highlighted the role of the characteristic length in controlling the thickness of the localized zone and the effect of the confining pressure in determining the pattern of shear band formation. An interesting feature emerging from the partially drained CPTu simulation results is the progressive formation of persistent shear bands, which originate from the cone tip and propagate outwards along the entire penetration depth.

Study on X-ray Induced Two-Dimensional Thermal Shock Waves in Carbon/Phenolic.

Carbon/Phenolic (C/P), a typical anisotropic material, is an important component of aerospace and often used to protect the thermodynamic effects of strong X-ray radiation. In this paper, we establish the anisotropic elastic-plastic constitutive model, which is embedded in the in-house code “RAMA” to simulate a two-dimensional thermal shock wave induced by X-ray. Then, we compare the numerical simulation results with the thermal shock wave stress generated by the same strong current electron beam via experiment to verify the correctness of the numerical simulation. Subsequently, we discuss and analyze the rules of thermal shock wave propagation in C/P material by further numerical simulation. The results reveal that the thermal shock wave represents different shapes and mechanisms by the radiation of 1 keV and 3 keV X-rays. The vaporization recoil phenomenon appears as a compression wave under 1 keV X-ray irradiation, and X-ray penetration is caused by thermal deformation under 3 keV X-ray irradiation. The thermal shock wave propagation exhibits two-dimensional characteristics, the energy deposition of 1 keV and 3 keV both decays exponentially, the energy deposition of 1 keV-peak soft X-ray is high, and the deposition depth is shallow, while the energy deposition of 3 keV-peak hard X-ray is low, and the deposition depth is deep. RAMA can successfully realize two-dimensional orthotropic elastoplastic constitutive relation, the corresponding program was designed and checked, and the calculation results for inspection are consistent with the theory. This study has great significance in the evaluation of anisotropic material protection under the radiation of intense X-rays.

CPINet: Parameter identification of path-dependent constitutive model with automatic denoising based on CNN-LSTM

Based on convolutional neural network (CNN) and improved long short-term memory (LSTM) neural network, a deep learning model CPINet is proposed for instant and accurate identification of path-dependent constitutive model parameters with excellent denoising performance. The elastic-plastic constitutive model with isotropic hardening is taken as an example for illustration. The results show that the CPINet can capture the intricate relationship between the strain field sequence and the non-temporal features (loading sequence and geometry dimensions) to identify constitutive parameters instantly and accurately. The denoising analysis revealed that the denoising processing and strain feature extraction of CNN provides excellent denoising ability to CPINet. Finally, the CPINet is validated by comparing the identified constitutive parameters of 6061 aluminum alloy with CPINet and finite element model updating method. To our knowledge, this is the first study that demonstrates the feasibility and considerable potential of using a deep learning technique to instantly and accurately identify constitutive parameters.

Experimental and numerical studies of T-shaped reinforced concrete members subjected to combined compression-bending-shear-torsion

The study of reinforced concrete members subjected to combined loads always has been an important research topic in the field of engineering, but the torsional behavior of T-shaped reinforced concrete members subjected to combined loads has yet to be determined. This paper is focused on providing a detailed explanation of the torsional behavior of T-shaped reinforced concrete members subjected to combined compression-bending-shear-torsion. From the perspective of experimental tests and numerical analyses, in this paper, we discuss the effects of combined loads on the torsion bearing capacity, the development of cracks and the failure mode, strains of key points in the concrete and longitudinal reinforcement, and the relation of torsion and angular displacement. We conducted experiments and numerical analyses of four groups of reinforced concrete members by using the main variables of the axial pressure ratio and the bending moment. Also, the experimental and calculated results are compared based on the elastic-plastic damage constitutive model of concrete. Based on the test data and the existing formula, we also extended the formula used to calculate the torsion bearing capacity and provided diagrams of the interaction when combined loads were applied. In addition, the results of this study highlight the turning point from torsion failure to compression-bending-torsion failure. The test results demonstrated that torsion capability increases in the specified range of axial pressure ratio and decreases as bending increases. The test results also indicate the importance of considering the effects of compression-shear-bending on the torsion bearing capacity in the engineering design.

Axial compressive behavior of laminated bamboo lumber columns with a chamfered section

The axial compressive behavior of laminated bamboo lumber (LBL) columns with a chamfered section was investigated using 15 specimens with lengths varying from 600 mm to 3000 mm; all considered samples had same square cross section of 100 mm × 100 mm with 10 mm chamfers at each corner. Axial compression tests were carried out to analyze the impact of slenderness ratios on failure modes, strain and ultimate bearing capacity of LBL columns. Two failure modes were observed i.e. compression failure and buckling failure. Obtained results on the ultimate vertical strain and ultimate load showed a downward trend with the increase in slenderness ratios; the correlation between the ultimate strain, ultimate load and the slenderness ratios were fitted. The approximate solution method was adopted to reveal the lateral deflections of buckling columns by a quartic functional model. Based on the ideal elastic–plastic constitutive model and Hill failure criterion, FEM was carried out to simulate the axial compression tests. The simulation results agreed well with both test and theoretical results, which verified the feasibility of proposed methods used under similar working conditions in this paper.

Modeling of Shear Crack Propagation in Rock Masses Using Mesh-Free LRPIM

The modeling of shear cracks in materials is critical in various engineering applications, such as the safety analysis of concrete structures and stability analysis of rock slopes. Based on the idea of Goodman element, the elastic-plastic constitutive model of the shear cracks is derived, and the elastic-plastic analysis of shear crack propagation is realized in the local radial basis point interpolation method (LRPIM). This method avoids the loss of accuracy caused by the mesh in the analysis of fracture propagation, and the crack propagation of rock brittle material is simulated. The investigation indicates that (1) the LRPIM results are close to the FDM results, which demonstrates that it is feasible to analyze shear cracks in rock masses. (2) Compared with the results of the built-in oblique crack model, when the LRPIM is used to analyze crack propagation, the results are close to the experimental results, showing that the LRPIM can model shear crack propagation in a rock mass. (3) The propagation path using the LRPIM is not sufficiently smooth, which can be explained as the crack tip stress and strain not being sufficiently accurate and still requiring further improvement.

Mechanical Properties and Elastic-Plastic Constitutive Model for Autoclaved Aerated Concrete Block

Mechanical Properties and Elastic-Plastic Constitutive Model for Autoclaved Aerated Concrete Block

Transversely Isotropic Constitutive Model of the Polypropylene Separator Based on Rich–Hill Elastoplastic Constitutive Theory

Abstract The polypropylene (PP) separator is a kind of transversely isotropic porous polymer film, and it is a key component of lithium-ion batteries. The mechanical properties of the separator affect the strength and security of lithium-ion batteries directly. However, the anisotropy behaviors of the separator remain unclear, which has led to inaccuracy of failure behaviors in lithium-ion battery. A large deformation elastic–plastic constitutive model of the PP separator was developed with the Rich–Hill large deformation elastoplastic constitutive theory. Besides, the hardening law of the PP separator was established according to the Hill yield criterion. The constitutive model accurately captured the anisotropy behaviors and the elastic–plastic process considering the large deformation of the separator. Numerical examples for model validation were presented and in good agreement with stress–strain data of tests up to the hardening stage.

A Thermal–Elastic–Plastic Constitutive Model using the Radial Basis Function Neural Network and Application for an Energy Efficient Warm Forming Process

This work presents a thermal–elastic–plastic constitutive equation based on the radial basis function (RBF) artificial neural network and application with the finite element (FE) analysis. In order to capture the stress data in the coupled temperature-strain doamin, a constitutive equation was defined based on the RBF model, and the trained model was validated by test data that were not used in the training. The RBF based constitutive model was then combined with the stress integration and tangent modulus formulation of FE analysis to apply the new model to a warm V-bending process that includes elastic–plastic deformation and elastic recovery under non-isothermal conditions. The heating method was the infrared (IR) local heating method. The results show that the RBF constitutive model can provide good agreement with the experimental data for V-bending in the non-isothermal conditions. The effects of the parameters of the basis function are also discussed in this work.

STUDY ON DAMAGE CONSTITUTIVE MODEL OF RECYCLED AGGREGATE CONCRETE IN CODE FOR DESIGN OF CONCRETE STRUCTURES AND DEVELOPMENT IN ABAQUS

Based on the damage constitutive of ordinary concrete in code for Design of Concrete Structures and considering the similarity of mechanical properties between recycled aggregate concrete and ordinary concrete, a uniaxial damage constitutive of recycled concrete was proposed. At the same time, the above model was programmed as a subroutine by FORTRAN language, and the subroutine was embedded into finite element analysis software ABAQUS to simulate and analyze the uniaxial compression mechanical properties of recycled concrete. The results of finite element simulation and test are compared from the aspects of stress-strain curve and damage evolution curve. The results show that the proposed elastic-plastic damage constitutive model can effectively represent the mechanical properties of recycled aggregate concrete under uniaxial compression at different substitution rates.

Fatigue life prediction of in-situ TiB2/2024 aluminum matrix composite

Fatigue performances of an in-situ TiB2 particle reinforced 2024-T4 alloy matrix composite (TiB2/2024Al) and 2024-T4 aluminum alloy (2024Al) were investigated. Stress- and strain-controlled fatigue experiments were conducted to obtain the fatigue lives. High-cycle fatigue performance was experimentally studied under different stress concentration levels. The results showed that the addition of in-situ particles enhances the fatigue resistance. A fatigue life prediction method was developed based on a damage-coupled Chaboche elastic–plastic constitutive model. Fatigue life predictions were performed using the established method and compared with the experiments. It was observed that the proposed method achieves fatigue life predictions with satisfactory accuracy.

Three-dimensional elastic-plastic damage constitutive model of wood

Abstract A 3D combined elastic-plastic damage constitutive model for wood is proposed within the theoretical framework of classical plasticity and continuum damage mechanics (CDM). The model is able to describe the various behavior of wood under loading, including the orthotropic elasticity, strengths inequality under tension and compression in each orthotropic direction, ductile softening under longitudinal compression, brittle failure under transverse tension, and parallel shearing, densification hardening under transverse compression. Hoffman criterion and a set of eight separate failure criteria were used to define wood yielding and damage initiation, respectively. Isotropic hardening was assumed after yielding and defined by an exponential type function. The constitutive model was implicitly discretized using backward Euler method, solved through the return mapping algorithm and implemented into ABAQUS through the user-defined material subroutine (UMAT). The proposed model was firstly verified by material property tests considering different stress states: monotonic and repeated tension and compression (in both parallel and perpendicular-to-grain directions), parallel-to-grain shearing, and the interactions between perpendicular-to-grain compression/tension and parallel-to-grain shearing, etc. Mechanical behavior of typical structural elements was further simulated to validate the proposed constitutive model.

Finite-element modeling of submarine landslide triggered by seismic loading in saturated cohesive soil deposits

Dynamic sliding process of submarine slope is a hotspot issue in ocean geotechnical engineering. Due to the lack of the numerical simulation method which could describe the dynamic characteristics of the saturated soft clay under seismic loading, few researches are reported on the dynamic sliding process of submarine slope in saturated cohesive soil deposits. Adopting the subroutine interface technology provided by ABAQUS platform, the undrained cyclic elastoplastic constitutive model, which could describe the dynamic characteristics of saturated soft clay, is programmed into user-defined material subroutine VUMAT and embedded in display dynamics analysis module of ABAQUS platform. Based on the cyclic elastic-plastic constitutive model and the updated Lagrangian technology, a numerical simulation method is proposed to investigate the dynamic sliding process of submarine soft clay slope under seismic loading. The applicability of the proposed numerical simulation method is verified by comparing with the previous research results. The results show that the strain accumulation characteristic makes the final accumulated deformation and shear strain larger than that of the conventional numerical modeling methods. When the general static constitutive model is used for dynamic analysis of slope, the analysis results are not conservative because the strain accumulation characteristic cannot be considered. Besides, it can display the whole dynamic sliding process of the slope, more intuitively predict the slope topography before and after earthquake, which could provide a reference for the planning and design of offshore structures.

An Orthotropic Elastic-Plastic Constitutive Model for Masonry Walls.

The use of a continuum structural model for the analysis of masonry structures in the plane stress state is discussed in this paper. Attention is paid to orthotropic masonry at the material level and validation of the model after its implementation in a proprietary finite element method (FEM) system via user-supplied subroutine. The constitutive relations are established in the framework of the mathematical elastoplasticity theory of small displacements and deformations. Based on the orthotropic failure criterion that was originally proposed by Hoffman in the spatial stress state, the model includes a generalization of the criterion in the plane stress. As it is the case for isotropic quasi-brittle materials, different yield surfaces are considered for tension and compression, which are both of Hoffman type.

Deformation Behavior of Superalloy Powder Compact under Hot Isostatic Pressing

Herein, the deformation behavior of a superalloy powder compact under hot isostatic pressing (HIP) is investigated by implementing an elastic–plastic constitutive model into the finite element analysis software MSC Marc. The coefficients of the constitutive model are obtained from interrupted HIP experiments. Finite element calculation results for the shape change of the powder compact under HIP agree well with the experimental results. Isothermal HIP and containerless HIP, both of which are based on finite element simulations, are conducted to study the dependence of the deformation on the container and temperature gradient. The stress state in all of the regions in the powder body deviates from the isostatic state of the compact even under isostatic pressing, due to the introduction of von Mises stress under the strong influence of the container. The temperature gradient is affected by the characteristic thermal conductivity and specific heat capacity of the porous powder body and container. Nonuniform temperature and stress distribution result in nonuniform densification, which eventually results in uneven powder compact shrinkage.

SPH Simulation of Structures Impacted by Tailing Debris Flow and Its Application to the Buffering Effect Analysis of Debris Checking Dams

Since the tailing dam fails catastrophically with substantial instantaneous deformation, it is difficult to measure the migration of debris flow caused by the failure of the tailings dam. A simulation model of tailing debris flow based on Smoothed Particle Hydrodynamics (SPH) theory of elastic-plastic constitutive equation has been established by considering the viscoplasticity of mud and the elastic-plastic characteristics of tailing sand to investigate the impact effect of tailing flow on the downstream structures. By comparing the experimental and two different simulation results obtained, it can be concluded that SPH elastic-plastic constitutive model can effectively simulate the accumulation and migration processes of the tailing debris flow, which indicates that the SPH model has good applicability to solve geotechnical large deformation problems of similar tailings flow slide. Then, the verified simulation model developed based on a series of simulations of tailing debris flow propagations was used to determine the momentum reduction on the downstream structure resulting from the presence of a simple checking dam perpendicular to the direction of propagation and to determine the characteristics of stresses applied to this structure in terms of peak impact force and evolution over time to the main flow direction.

Bending induced wrinkling and creasing in axially crushed aluminum tubes

Concertina folding of tubes used for impact mitigation bends the tube section to tight curvatures that can lead to failures on the tensioned side of the folds. This paper reports results from such axial crushing experiments on Al-6061-T6 circular tubes in which cleft-like features were also observed on the compressed sides of folds. Microscopic examination of the compressed sides of sectioned folds at different stages of bending revealed the following. Compression leads to surface wrinkles that are initiated by small initial surface roughness. Further bending increases the amplitude of the wrinkles, and at even higher bending the wrinkles morph into folds, creases, and sharp discontinuities. Metallographic examination of these surface undulations revealed that surface wrinkles encompass several grains, which deform conforming to the imposed local geometric changes. With this in mind, the axial crushing was simulated at the continuum level via an axisymmetric finite element analysis coupled with a suitably calibrated non-quadratic elastic–plastic constitutive model. A sufficiently refined mesh and representative initial surface imperfections enabled monitoring of the evolution of surface instabilities on the compressed sides of folds. Surface wrinkles appear at compressive strains of about 50%. As the local bending increases, their amplitude grows, and subsequently they evolve into local folds, and creases that resemble surface features observed in the experiments.

Fracture mechanics testing and crack propagation modelling in polypropylene pipes

PurposeThe main aim of this study is to determine the fracture toughness and accordingly to predict the fracture initiation, crack propagation and mode of crack extension accurately in polypropylene subsea pipes subjected to internal pressure.Design/methodology/approachTensile test was performed following the ISO 527–1 standard. An elastic-plastic constitutive model was developed based on the tensile test results, and it is implemented in the FEA model to describe the constitutive behaviour of the polypropylene material. Three-point bend tests with linear-elastic fracture mechanics (LEFM) approach were conducted following ISO-13586 standard, from which the average fracture toughness of the polypropylene pipe material in crack-opening mode was found as KIc = 3.3 MPa√m. A numerical model of the experiments is developed based on the extended finite element method (XFEM), which showed markedly good agreement with the experimental results.FindingsThe validated XFEM modelling approach is utilised to illustrate its capabilities in predicting fracture initiation and crack propagation in a polypropylene subsea pipe subjected to an internal pressure containing a semi-elliptical surface crack, which agrees well with existing analytical solutions. The XFEM model is capable of predicting the crack initiation and propagation in the polypropylene pipe up to the event of leakage.Originality/valueThe methodology proposed herein can be utilised to assess the structural integrity and resistance to fracture of subsea plastic pipes subjected to operational loads (e.g. internal pressure).