Elastoplastic Damage Constitutive Model Research Articles

Numerical implementation, comparison and validation of a pressure dependent model for polymer composites

A pressure-dependent elastoplastic damage constitutive model for polymer composites is established, in which the Implicit and Explicit numerical algorithm has been implemented in ABAQUS/Standard in terms of elasto-plastic phase with the aid of UMAT. The off-axis tension/compression tests for T800H/3633,T800S/3900-2B carbon/epoxy laminated composites, and quasi-isotropic compression tests for T800H/3633 laminated composites, have been simulated, in order to validate the efficiencies and accuracies of two algorithms. Additionally, the open-hole compression simulation is employed to analyze the progressive failure of T800H/3633 laminated composites. Compared with the Implicit and Explicit algorithm based the elasto-plastic model, the Explicit algorithm is recommended based on the computational efficiency on the premise of ensuring the numerical convergence, which may be extended to the large-scale engineering applications either statics or dynamics. Furthermore, the open-hole compression simulation of T800H/3633 composites shows the developed elasto-plastic damage model can predict well the stiffness and strength properties of the specimen. The failure mode and deformation of the open-hole specimen of T800H/3633 composites are also briefly discussed.

Numerical simulation and experimental verification studies on a unified strength theory-based elastoplastic damage constitutive model of shale

The purpose of this study is to establish an elastic–plastic damage constitutive model of shale and simulate the elastic–plastic damage characteristics of shale under stress. Based on the unified strength theory and the mechanics of shale rock samples characterized in laboratory tests, a new elastic–plastic damage constitutive model for shale is established by introducing compression factors and damage variables. The main considerations include the compressibility of primary fractures and pores in the shale core, and the formation of secondary cracks in the rock matrix under stress. A fully implicit backward Euler regression mapping algorithm has been used to solve the model, and the numerical simulation results are in good agreement with the experimental results. The results show that the model established in this paper can accurately simulate the elastic–plastic damage characteristics of shale under stress, and that it provides a new numerical simulation method for describing the elastic–plastic damage in shale.

Coupled Hydrologic-Mechanical-Damage Analysis and Its Application to Diversion Tunnels of Hydropower Station

Since the traditional model cannot sufficiently reflect the multifield coupling problem, this paper established an elastoplastic stress-seepage-damage analysis model considering the seepage field, stress field, and damage field. Simultaneously, the elastoplastic damage model involves many parameters and is difficult to determine. An inverse analysis program is compiled based on the differential evolution algorithm, and the surrounding rock damage parameters are inverted. Finally, the elastoplastic stress-seepage-damage coupling program and the damage parameter displacement back analysis program is compiled using C++ language. Then, the program is used to calculate the coupling problem of tunnel elastoplastic stress-seepage-damage. The results show that the proposed elastoplastic damage constitutive model can well describe the mechanical behavior of rock. The computational procedure can also simulate practical engineering problems, which can provide specific guidance for site construction.

Application of constitutive model in simulation analysis of tunnel construction

Application of constitutive model in simulation analysis of tunnel construction

Dynamic Properties Test and Constitutive Relation Study of Lightweight Aggregate Concrete under Uniaxial Compression

For the purpose of studying the dynamic properties of lightweight aggregate concrete, dynamic performance tests under uniaxial compression were conducted by considering 10 different strain rates ranging from 10−5/s to 10−1/s, from which the stress‐strain curves under various compressive loads were obtained. From the stress‐strain curves, parameters including peak stress, peak strain, and elastic modulus of lightweight aggregate concrete, as well as the concrete failure mode, were determined and examined. By reviewing the relevant literature on ordinary concrete, the dynamic properties of lightweight aggregate concrete were analyzed accordingly. Meanwhile, by applying the dynamic elastoplastic damage constitutive model, the effect of dynamic rate on lightweight aggregate concrete was calculated. The experimental results showed that the damage mode of lightweight aggregate concrete under the static and dynamic strain rates belonged to shear failure, which is different from that of ordinary concrete (binding material failure). On the other hand, it was also found that the peak stress and elastic modulus of lightweight aggregate concrete could be increased by 54.48% and 28.75%, respectively, with the increase of strain rate, suggesting that the loading strain rate has a stronger influence on lightweight aggregate concrete than on ordinary concrete. Based on the experimental data, both the peak stress and nondimensionalized elastic modulus are in linear relationship with the logarithm of the nondimensionalized strain rate. Moreover, the established constitutive model had been verified as an effective and reliable tool for simulating the dynamic rate effect of lightweight aggregate concrete.

On the combination of nonlinear load effects of structures

A new method for combination of nonlinear load effects of structures is suggested in the paper. At first, the concepts of load combination and load effect combination are discussed, respectively. A load combination method based on probability space partition is introduced, through which the load effects of structures could be accurately estimated. Afterwards, the principle of nonlinear load effect combination of structures under multiple loads is presented. In order to reflect the nonlinear performances of structures, the physical equations of solid mechanics with a reasonable elastoplastic damage constitutive model are applied to derive structural deterministic nonlinear responses. The probability density evolution equation (PDEE) is used to acquire the stochastic response characteristics of structures under multiple random loads. Hence, the combination of nonlinear load effects of structures is well realized. Furthermore, the reliability of structures under multiple loads is evaluated by using the physical synthesis method. Finally, in order to illustrate the proposed method, the nonlinear load effect combination analyses for a reinforced concrete (RC) plane frame under gravity load and earthquake and a concrete bridge under long-term vehicular loads and earthquakes are carried out. The analysis results demonstrate the applicability and superiority of the proposed method.

Failure mechanism analysis of fiber-reinforced polymer composites based on multi-scale fracture plane angles

This paper proposes a physically sound elasto-plastic damage constitutive model, through following Mohr's fracture hypothesis, to characterize pressure sensitivity, nonlinear behaviors and isotropic damage of epoxy matrix materials. Upon the consideration with geometric non-uniformities and mechanical behaviors of constituents, a micromechanical analysis is carried out to study failure mechanisms within fiber-reinforced polymer composite materials applied by different loading scenarios. In particular, special focus is given to the values and distributions of fracture plane angles on multi-scales - the fiber scale and the lamina scale, and therefore both damage scenarios and dominant failure mechanisms are further revealed. The influence of shear nonlinearity of epoxy matrix on overall composite shear responses is assessed from a parametrical study, showing that the composite response induced by longitudinal shear is more susceptible the matrix shear property, when comparing with transverse shear. At last, another use of the proposed micromechanical model is presented. With the use of strength properties and fracture angles captured by micromechanics, the parameters (R⊥At, p⊥⊥t and p⊥⊥c) in Puck's criterion can be computed without making any assumption sometimes arguable. In general, the numerical results regarding homogenized stress-strain responses as well as fracture morphology agree well with experimental measurements and theoretical analyses, validating the predictive capacity of the proposed model.

Seismic analysis of a transition tunnel constructed with TBM and mining method

A transition tunnel is generally built to connect a TBM tunnel and a mining tunnel, given the different cross sections associated with each construction method. The transition tunnel may be sensitive to earthquake damage since the tunnel cross-section and stiffness change along the tunnel axis. Studying the seismic performance of the transition tunnel structure, a subtle 3D finite element model is carried out. Comparing with the calculation results of SHAKE91, a reasonable non-reflective boundary condition is used. The concrete adopts an elastoplastic damage constitutive model, and the surrounding rock mass uses an elastoplastic constitutive model based on the Drucker-Prager yield criterion. The effects of different ground motion magnitudes and different types of seismic waves are calculated and analyzed through dynamic time-history method. The calculation results show that the impact range of the construction method butted composite lining section on the tunnel structure of the mine tunnel and the TBM tunnel is about 10m, and the reinforcement of the inner lining will cause a sudden change in the stress of the outside TBM tunnel structure. Moreover, the compressive stress of the surrounding rock and tunnel structure is small, and the structural damage mainly occurs in the area of the arch shoulder and arch foot.

An elastoplastic damage constitutive model for frozen soil based on the super/subloading yield surfaces

Soil particles and ice form bonded structure in frozen soil. The modulus and bond strength of frozen soil decrease with the damage of the bonded structure during deformation. An elastoplastic damage constitutive model, based on the super/subloading yield surfaces, is proposed for frozen soil, in which the damage variable and bond strength are used to consider the elastic and plastic damage respectively. The model is validated with the observed mechanical behaviors of frozen sandy soil and frozen saline soil in triaxial compression tests with different confining pressures. The comparisons illustrate that the model can describe the hardening/softening and dilatancy of frozen soils with the change of confining pressures. The results also show that the expansion of frozen soil during shear is related to the loss of bond strength induced by the development of damage of the bonded structure.

Simulation and experimental verification of the non-uniform corrosion cracking process of reinforced mortar specimen

To better study the non-uniform corrosion cracking process of reinforced mortar specimens, the numerical simulation has been carried out from the perspective of meso-mechanics. By applying X-ray CT technology to extract the distribution of pores, a reinforced mortar model was established, containing large pores and mortar matrix. An elastoplastic damage constitutive model of mortar was proposed based on parallel spring theory, by which the differences between tensile and compressive damage are considered. Combined with Digital Volume Correlation (DVC) technology, the non-uniform corrosion expansion displacement field of the reinforcement surface was obtained as load, and was applied in the numerical simulation. Using the finite element analysis software ABAQUS, the whole non-uniform corrosion cracking process of reinforced mortar was simulated. The damage development process of this numerical model was then verified by the DVC calculation results at specific times. In addition, the differences between the damage development of reinforced mortar model under non-uniform and uniform corrosion displacement loads are discussed.

A microscopic elasto-plastic damage model for characterizing transverse responses of unidirectional fiber-reinforced polymer composites

Abstract A phenomenological-based micromechanical method, comprising the coupling of the matrix constitutive model and the cohesive zone (CZM) model at fiber-matrix interfaces, is presented to investigate the mechanical behaviors of unidirectional (UD) fiber-reinforced polymer (FRP) composites subjected to transverse tension and compression. The key point of this method is the establishment of a novel elasto-plastic damage constitutive model using a fracture plane based yield criterion. Both plastic deformation and progressive failure procedure is incorporated in the implicit simulation. Special focus is given to the determination of the input values of constituent material properties, suggesting that directly using the macroscopic matrix properties to characterize the mechanical responses at the microscale level may bring large discrepancies in homogenized stress-strain responses of UD composites. A parametrical study is also carried out to calibrate cohesive parameters. The numerical results, in good agreement with experimental measurements, clearly reveal the damage scenarios and the dominant failure mechanisms. It can be concluded that the debonding of the fiber-matrix interfaces is responsible for the ultimate transverse tensile strength, while compression failure is governed by two possible modes, i.e. matrix compressive failure if matrix failure firstly occurs, and matrix tensile and interface debonding failure when debonding initiates first. Besides, the distribution of fracture plane angles in matrix is examined to further validate the predictive capacity of the proposed model.

Stress-seepage-damage coupling modelling method for tunnel in rich water region

PurposeThis paper aims at the problem of surrounding rock excavation damage zone of tunneling in the rich water region, this paper aims to propose a new seepage-stress-damage coupling model and studied the numerical algorithm. This reflects the characteristics of rock damage evolution, accompanied by plastic flow deformation and multi-field interaction.Design/methodology/approachFirst of all, rock elastoplastic damage constitutive model based on the Drucker–Prager criterion is established, the fully implicit return mapping algorithm is adopted to realize the numerical solution. Second, based on the relation between damage variation and permeability coefficient, the rock stress-seepage-damage model and multi-field coupling solving iterative method are presented. Finally, using the C++ language compiled the corresponding programs and simulated tunnel engineering in the rich water region.FindingsResults show that difference evolution-based back analysis inversed damage parameters well, at the same time the established coupling model and calculating program have more advantages than general conventional methods. Multiple field coupling effects should be more considered for the design of tunnel support.Originality/valueThe proposed method provides an effective numerical simulation method for the construction of the tunnel and other geotechnical engineering involved underground water problems.

An elastoplastic damage constitutive model of concrete considering the effects of dehydration and pore pressure at high temperatures

Pore pressure and thermal dehydration of concrete are two major factors which affect the spalling of concrete at high temperatures. Thermal dehydration can cause deterioration of concrete properties and promote the development of micro cracks in the skeleton of concrete. Pore pressure will also be influenced by dehydration when the hydrated water enters the micro pores. In the current study, a framework of elastoplastic damage constitutive model is developed to described the mechanical behaviour of concrete and pore pressure at high temperatures. Both load induced damage and thermal dehydrated damage are considered. The thermal dehydrated damage is temperature related, which reflects the impact of temperature on concrete properties. A model of pore pressure is developed by considering the influence of thermal dehydration and damage related permeability. The pore pressure field associated with vapor, liquid water and dry air is predicted and compared with experimental results.

Study on structural failure mechanism of explosive separation device based on the damage constitutive model

The explosion separation device is the critical factor to ensure the effective separation of the payload and the launch vehicle. The rationality of the structural strength is usually assessed by the real explosion separation test. The separation of components in the deformation and damage is difficult to be obtained. The traditional method, based on the elasto-plastic constitutive, is also unable to simulate the damage of each component in the separation. The traditional strength check can be calculated by the elasto-plastic constitutive relation for large deformation, while the damage simulation can only be obtained by the progressive damage fracture. The metal material dynamic damage constitutive is applied based on the ABAQUES to simulate the damage and failure of the explosion separation. Then the finite element model of the explosion separation device can be established based on the elasto-plastic damage constitutive model, and the process of the ground test of the explosive separation device can be reproduced by the simulation of the corresponding FEM model. And then the weakness of the explosive separation device is finally determined by the calculation results. The experimental results are consistent with the simulation, which confirms the accuracy of the proposed method. The solution idea provides a reference basis for the product design and dynamic damage simulation.

Constitutive modeling of steel fiber-reinforced concrete

Experimental studies within the previous years showed that the behavior of concrete is improved by adding steel fibers. Due to bridging effect, steel fibers in a concrete matrix prevent crack propagation under static loads. This phenomenon increases the load-bearing capacity of steel fiber-reinforced concrete, specifically after the peak load. In contrast to similar studies, in this study the effect of fibers on steel fiber-reinforced concrete is directly described based on uniaxial compressive and tensile stress–strain curves. For this purpose, the effect of fiber on the stress variations is extracted from the difference between steel fiber-reinforced concrete and its corresponding concrete matrix uniaxial stress–strain curves. These differential stress curves were extracted from 103 experimental specimens, collected from the literature. Then, some equations were developed for them with appropriate accuracy, using genetic programming technique. These equations were only based on primary specifications of fibers and concrete matrix. In the next stage, an elastoplastic damage constitutive model initially developed for plain concrete was modified, using the developed steel fiber-reinforced concrete modeling equations. The proposed model was implemented in a finite element analysis software and successfully simulated the steel fiber-reinforced concrete behavior subjected to uniaxial and flexural experiments.

Mechanical behavior of low-rank bituminous coal under compression: An experimental and numerical study

The mechanical behavior of coal has an important influence on coal reservoir stimulation and the dynamic change of coal reservoir permeability during coalbed methane (CBM) production. Generally, coal is regarded as an elastic-brittle material, which is reasonable when the surrounding stress is small. However, with the increasing depth of CBM exploitation, the in-situ stress increases continuously, so the coal will inevitably show some plastic behavior. In this work, the typical low-rank bituminous coal from the Baode CBM block on the eastern margin of the Ordos Basin was selected to carry out uniaxial and triaxial compression tests under various confining pressures (Pc) for further investigation of mechanical behavior. The results show that, as a complex porous material, the coal samples have a series of deformation responses during the loading process, which can be classified into four phases. Both the yield stress (σy) and the peak stress (σpeak) increase nonlinearly as Pc increases. Additionally, with increasing Pc, the elastic modulus (E) increases at a decreasing rate, while the Poisson's ratio (ν) decreases at a decreasing rate. Moreover, a change from volumetric compressibility to dilatancy in the coal was clearly observed in the tests, and the stress at the onset of dilation (σd) is also significantly influenced by Pc. Finally, based on irreversible thermodynamics and empirical support, a coupled elastoplastic damage constitutive model for low-rank bituminous coal was established by introducing the non-associated plastic flow laws and the damage evolution rules; the numerical simulation result of the model is in good agreement with the experimental measurements. This model can be used for further investigation of the mechanical properties of coal reservoirs under different in-situ stress conditions during the exploitation of CBM.

Formation mechanism and characterization of shear band in high-speed cutting Inconel718

Nickel-based alloy Inconel718 is one kind of complex alloy with multiple components. There is complex cutting deformation (shear localization of material) in high-speed cutting process. The chip shows a serrated shape. Through analyzing the chip morphology, the change of microstructure and development of shear band is analyzed, and the formation mechanism of the shear band is revealed. Based on the formation mechanism of shear band, the coupled elastoplastic-damage constitutive model is proposed to describe the shear stress during the cutting process. The shear band width has been determined by micrographic observations and theoretical model calculation. The experimental and theoretical results show that the shear band width in chip formation decreases linearly with an increase in the cutting speed.

Experimental and modeling investigation on the dynamic response of granite after high-temperature treatment under different pressures

In this work, the dynamic compressive mechanical properties of Beishan granite are investigated under the condition of uniaxial load and confined pressure, respectively. The purpose of this investigation is to study the effect of hydrostatic pressure and pre-heating temperature on the strength property and failure of such material. The investigation is carried out with the use of a large-diameter split-Hopkinson pressure bar (SHPB), which is equipped with an active confining device. The dynamic stress–strain behaviors of the granite samples under different confined conditions are obtained with a pre-heating temperature ranging from 25 to 800°C. We analyzed the temperature-dependent variation of the peak stress, peak strain and elastic modulus of the material under selected values of confined pressure. It is observed that the uniaxial compressive behavior of Beishan granite under unconfined pressure is strongly dependent on the pre-heating temperature. The values of the peak stress and the elastic modulus both decrease as the pre-heating temperature increases, while the value of the peak strain increases with the rise of pre-heating temperature, indicating a characteristic change from elastic-brittle to elastic–plastic. Under confined pressure, the strength of the material can be greatly improved, and higher pre-heating temperature tends to bring down the value of the strength. With the confined configuration, the strengthening of the peak stress is not significantly associated with the value of the confined pressure; instead the dependence on the strain rate becomes more remarkable. For the temperature effect, the value of the peak stress can be linearly correlated with the temperature level through comparative analysis. Moreover, the elastic modulus of the material can be associated with the temperature by a functional form, known as the temperature shift factor. Finally, an elastoplastic-damage constitutive model is established to predict the dynamic mechanical behavior of the material after high-temperature treatment under different confined pressures.

A Nonlinear Damage Model of Hardening-Softening Materials

In this paper, an elastoplastic-damage constitutive model is presented. The formulation is cast within the framework of continuum damage mechanics (CDM) by means of the internal variable theory of thermodynamics. The damage is assumed as a tensor type variable and its evolution is developed based on the energy equivalence hypothesis. In order to discriminate the plastic and damage deformation, two surfaces named as plastic and damage are introduced. The damage surface has been developed so that it can model the nonlinear variation of damage. The details of the model besides its implicit integration algorithm are presented. The model is implemented as a user-defined subroutine user-defined material (UMAT) in the abaqus/standard finite element program for numerical simulation purposes. In the regard of investigating the capability of model, the shear and tensile tests are experimentally conducted, and corresponding results are compared with those predicted numerically. These comparisons are also accomplished for several experiments available in the literature. Satisfactory agreement between experiments and numerical predictions provided by the model implies the capability of the model to predict the plastic deformation as well as damage evolution in the materials.

An anisotropic elastoplastic damage constitutive model for 3D needled C/C-SiC composites

This paper established a combined elastoplastic damage model to analyze the nonlinear mechanical behavior of 3D needled C/C-SiC composites. Inelastic deformation and stiffness degradation of the composite were characterized by the plasticity and damage theories. An innovative plastic potential function containing variable parameters was proposed to consider particularly the anisotropy of plastic deformation in each material direction. Based on the Weibull statistical distribution of the material strength, an exponential damage state function was established to characterize stiffness degradation for the composite in each material direction. Parameters of this constitutive model were determined from experiments data. It can be found that the nonlinear stress-strain curves for the composite under off-axis tensile and shear loadings can be accurately described by the model. The yield and damage surfaces of the composite were also studied. Finally, the constitutive model was validated by analyzing the mechanical behavior of a composite plate containing a center-hole subjected to tensile load.