Creep mechanism and creep constitutive model of aluminum silicate short-fiber-reinforced magnesium matrix composite

By the constant stress tensile creep test method, creep tests were performed on aluminum silicate short fiber-reinforced AZ91D magnesium matrix composite with volume fraction of 30% and its matrix alloy AZ91D under different temperatures and stresses. The results indicate that the composite and the matrix have the same true stress exponent and true activation energy for creep, which are 3 and 144.63 kJ/mol, respectively. The creep of the composite is controlled by the creep of its matrix, which is mainly the controlling of viscous slip of dislocation, and the controlling of grain boundary slippage as a supplement. The creep constitutive model obtained from the experiment data can well describe the creep deformation pattern of the composite.

BASIC SOLUTION FOR THE THREE-PHASE COMPOSITE CONSTITUTIVE MODEL IN ANTIPLANE PIEZOELECTRICITY

A basic solution in series form for the three-phase composite cylindrical model in antiplane piezoelectricity subjected to the action of a singularity in the intermediate matrix region is presented. The solution is obtained through the complex potential approach in conjunction with the techniques of analytical continuation, singularity analysis, Laurent series expansion in an annular region and Cauchy integral formulae, etc. Based on the complex potentials obtained, explicit expressions for the distribution of stress and electric displacement in the three regions are also derived.

ARC INTERFACE CRACK IN A THREE-PHASE PIEZOELECTRIC COMPOSITE CONSTITUTIVE MODEL

An in-depth investigation is made on the problem of an arc-shapedinterface insulating crack in a three-phase concentric circularcylindrical piezoelectric composite constitutive model. An exactsolution in series form is derived by employing the complex variablemethod. In addition, the distribution of physical quantities such asstresses, strains, electric displacements and electric fields in thewhole field and along the interface is also presented.

Mechanical behaviors of backfill-rock composites: Physical shear test and back-analysis

The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence.For exposing the shear failure mechanism of backfill-rock composites,we conducted shear tests on backfill-rock composites under three constant normal loads,compared with the unfilled rock.To investigate the macro-and meso-failure characteristics of the samples in the shear tests,the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring.In parallel with the experimental test,the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process.Based on the damage mechanics and statistics,a novel shear constitutive model was proposed to describe mechanical behavior.The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve,i.e.the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill.Moreover,the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages,i.e.the shear failure of the specimens experienced:stage I:stress concentration;stage II:crack propagation;stage III:crack coalescence;stage IV:shearing friction.The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfillrock composites.Based on damage mechanics and statistics,a shear constitutive model was proposed to describe the shear fracture characteristics of specimens,especially the bimodal phenomenon.Finally,the micro-and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results.The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.

Comparative Study on Constitutive Models to Predict Flow Stress of Fe-Cr-Ni Preform Reinforced Al-Si-Cu-Ni-Mg Composite

The isothermal compression tests were carried out on Gleeble-3500 thermal-mechanical simulation machine in a temperature range of 298-473 K and strain rate range of 0.001-10 s^-1. The experimental results show that the flow stress data are negatively correlated with temperature for temperature softening, and the strain rates sensitivity of this composite increases with elevating temperature. Based on the experimental data, Johnson-Cook, modified Johnson-Cook and Arrhenius constitutive models were established. The accuracy of these three constitutive models was analyzed and compared. The results show that the values predicted by Johnson-Cook model could not agree well with the experimental values. The prediction accuracy of Arrhenius model is higher than that of Johnson-Cook model but lower than that of the Modified Johnson-Cook model.

A uniaxial tensile constitutive equation of high-ductility cementitious composites

In order to establish the constitutive relationship of high-ductility cementitious composites(HDCCs)under uniaxial tensile load and to guide the structural design of HDCCs,based on the analysis of the existing uniaxial tensile constitutive relationship and ideal elastoplastic linear strain-hardening model,a bilinear tensile constitutive equation of HDCCs was proposed.The points of nominal initial cracking and nominal maximum stress were adopted as control points of the line segment,and the constitutive relationship of HDCCs was established.Five series of uniaxial tensile stress-strain curves of HDCCs were combined to perform an experimental application of the constitutive equation,along with an analysis of the key parameters.The experimental results confirm the ability of the constitutive equation to overcome the problem of insufficient or excessive redundancy of existing models in terms of calculation bearing capacity.Specifically,the measured maximum stress value is larger than the nominal value,and the ratio between the two values ranges from 1.08 to 1.22.Additionally,the tensile strain at the softening point obtained by fitting a straight line with the valley points of the strain-hardening stage curve is greater than or equal to the tensile strain at the measured maximum stress point and the ratio of the fitted values to the measured values ranges from 1.00 to 1.19.

One-dimensional Incremental Constitutive Relation of SMA Wire Reinforced Smart Composites with Damages

A new Martensitic transformation kinetic model for shape memory alloy （SMA） is proposed based on the phenomenological description of the Martensitic transformation heat flow-temperature curve and on the linear relationship between the partial derivatives of Martensite fraction and of Gbbis free energy with respect to the temperature. A meso-mechanical model is developed to describe the longitudinal stiffness reduction and thermo-dilatation variation of the composites caused by fiber breaking or fiber peeling off the base material. One-dimensional incremental constitutive relation is then established for SMA wire reinforced smart composites with damages by introducing three parameters to respectively describe the extent of fiber breaking, fiber peeling off the base material and interface weakening. The results presented herein may provide a theoretical basis for further studying on SMA smart composites with damages.

Dynamic mechanical behavior and nonlinear hyper-viscoelastic constitutive model of SiO_(2) particle-reinforced silicone rubber composite:experimental and numerical investigation

SiO_(2)-particle reinforced silicon rubber composite(SP-RSRC)is a widely utilized material that offers shock absorption protection to various engineering structures in impact environments.This paper presents a comprehensive investigation of the mechanical behavior of SP-RSRC under various strain rates,employing a combination of experimental,theoretical,and numerical analyses.Firstly,quasi-static and dynamic compression tests were performed on SP-RSRC utilizing a universal testing machine and split Hopkinson pressure bar(SHPB)apparatus.Nonlinear stress-strain relationships of SP-RSRC were obtained for strain rates ranging from 1×10^(−3) to 3065 s^(−1).The results indicated that the composite showed evident strain rate sensitivity,along with nonlinearity.Then,a nonlinear visco-hyperelastic constitutive model was developed,consisting of a hyperelastic component utilizing the 3rd-order Ogden energy function and a viscous component employing a rate-dependent relaxation time scheme.The model accurately characterized the dynamic mechanical response of SP-RSRC,effectively mitigating the challenge of calibrating an excessive number of material parameters inherent in conventional viscoelastic models.Furthermore,the simplified rubber material(SRM)model,integrated within the LS-DYNA software,was chosen to depict the mechanical properties of SP-RSRC in numerical simulations.The parameters of the SRM model were further calibrated based on the strain-stress relationships of SP-RSRC,as predicted by the developed nonlinear visco-hyperelastic constitutive model.Finally,an inverse ballistic experiment using a single-stage air gun was conducted for SP-RSRC.Numerical simulations of SHPB experiments and the inverse ballistic experiment were then performed,and the reliability of the calibrated SRM model was verified by comparing the results of experiments and numerical simulations.This study offers a valuable reference for the utilization of SP-RSRC in the realm of impact protection.

Damage evolution model of strain hardening cementitious composites under the uniaxial stress state

The deformation and damage behaviors of strain hardening cementitious composites （SHCC） under the uniaxial stress state were investigated in this paper. Two ductile failure-based constitutive models were introduced to describe the uniaxial tension and compression properties of SHCC only using a few parameters. The computation method of model parameters was developed to ease the simulation procedures. Damage evolution of the SHCC was simulated by the formulation of continuum damage mechanics subsequently. The results show that the proposed models fit the stress-strain curves reasonably well, and the damage variables show different growth rules under uniaxial tension and compression. It is concluded that the proposed method can not only simply simulate the constitutive behavior of SHCC with the reasonable accuracy but also capture the characteristic of material degradation.

Hot deformation behavior and microstructure evolution of Be/2024Al composites

The high temperature compression test of Be/2024Al composites with 62wt%Be was conducted at 500–575℃ and strain rate of0.003–0.1 s^(-1).The strain-compensated Arrhenius model and modified Johnson–Cook model were introduced to predict the hot deformation behavior of Be/2024Al composites.The result shows that the activation energy of Be/2024Al composites was 363.364 k J·mol^(-1).Compared with composites reinforced with traditional ceramics,Be/2024Al composites can be deformed with ultra-high content of reinforcement,attributing to the deformable property of Be particles.The average relative error of the two models shows that modified Johnson–Cook model was more suitable for low temperature condition while strain-compensated Arrhenius model was more suitable for high temperature condition.The processing map was generated and a hot extrusion experiment was conducted according to the map.A comparation of the microstructure of Be/2024Al composites before and after extrusion shows that the Be particle deformed coordinately with the matrix and elongated at the extrusion direction.

Compression behavior and constitutive model establishment of fly ash cenosphere/polyurethane aluminum alloy syntactic foam

The aluminum matrix syntactic foam was fabricated by pressure infiltration technique,and the filling material is syntactic foam material with fly ash cenosphere as the main component and polyurethane foam as the binder.Split Hopkinson pressure bar(SHPB)dynamic compression and quasi-static tests were carried out to examine the compressive response of syntactic foam in this study.Then the dynamic constitutive model was established.Results show that the compressive stress-strain curve of syntactic aluminum foam is similar to that of other metallic foam materials:both kinds of aluminum matrix syntactic foams have strain rate effect,and the syntactic foam has higher compressive strength and energy absorption than the same density aluminum foams.However,due to the different sizes of cenospheres,the dynamic compression results of two kinds of syntactic foams are different,and the energy absorption effect of syntactic foam with small size under dynamic impact is the best.In the range of strain rate and density studied experimentally,the curves of constitutive model fit well with the curves of experimental data.

Application of interpolated double network model for carbon nanotube composites in electrothermal shape memory behaviors

Multi-wall carbon nanotube filled shape memory polymer composite(MWCNT/SMC)possessed enhanced modulus,strength,and electric conductivity,as well as excellent electrothermal shape memory properties,showing wide design scenarios and engineering application prospects.The thermoelectrically triggered shape memory process contains complex multi-physical mechanisms,especially when coupled with finite deformation rooted on micro-mechanisms.A multi-physical finite deformation model is necessary to get a deep understanding on the coupled electro-thermomechanical properties of electrothermal shape memory composites(ESMCs),beneficial to its design and wide application.Taking into consideration of micro-physical mechanisms of the MWCNTs interacting with double-chain networks,a finite deformation theoretical model is developed in this work based on two superimposed network chains of physically crosslinked network formed among MWCNTs and the chemically crosslinked network.An intact crosslinked chemical network is considered featuring with entropic-hyperelastic properties,superimposed with a physically crosslinked network where percolation theory is based on electric conductivity and electric-heating mechanisms.The model is calibrated by experiments and used for shape recoveries triggered by heating and electric fields.It captures the coupled electro-thermomechanical behavior of ESMCs and provides design guidelines for MWCNTs filled shape memory polymers.

ON THE DESCRIPTION OF ANISOTROPIC DAMAGE IN COMPOSITE LAMINATES

A general anisotropic damage theory of cracked laminates is formulated here.The deformation of composite laminates is composed of matrix elastic strains,pseudo-elastic damage strains due to cracking and permanent damage strains due to interlaminar slip.The surface of damage initiation is constructed accord- ing to the concept of linear elastic fracture mechanics for the virgin material.After the initial damage,a pesudo-elastic damage can be used to describe the damage behaviour if interlaminar slip is negligible.Damage evolution,load induced anisotropy and interlaminar-intralaminar interaction for composite laminates are exam- ined;the latter can perturb the normality structure of damage strain rate.Explicit expressions are given for pseudo-elastic (or secant) moduli of the damaging composite laminates,under a non-interacting assumption imposed on the cracks between different families.

基于双模量理论的连续配筋混凝土复合式路面沥青层表损伤分析及Top-Down开裂控制

基于连续介质损伤力学和双模量理论,建立单一模量和双模量2种疲劳损伤本构,采用数值模拟的方法,对2种疲劳损伤本构模型进行了简单分析对比,并采用双模量损伤本构分析沥青层(AC)厚度、模量、拉压模量比以及AC层与连续配筋水泥混凝土层(CRC)摩擦系数4个因素对沥青层表面损伤的影响,在单因素分析的基础上通过响应面法对CRC+AC复合式路面抗Top-Down开裂性能进行优化设计。研究表明:AC层在单模量下的最大压应力比双模量下大0.1MPa,但AC层在单模量下几乎未产生拉应力,而双模量下的最大拉应力为0.08MPa;单因素分析得到AC层厚度、模量、拉压模量比、层间摩擦系数推荐最大取值分别为8cm、1700MPa、0.8、7;3个参数中,对AC层表面疲劳损伤度综合影响从大到小的组合为:AC层厚度和拉压模量比,AC层拉模量和拉压模量比,AC层厚度和拉模量;针对不同拉模量的AC层材料提出了不同AC层厚度下的拉压模量比控制标准。

考虑组构演化的砂砾土弹塑性本构模型

考虑组构演化效应对于真实、准确地描述无黏性土在循环加载过程中的宏观力学行为具有重要意义。在砂砾土单调加载条件下构建的非线性剪胀方程的基础上,引入反映其循环荷载条件下剪胀阶段组构演化的剪胀内变量,基于广义塑性理论框架建立了反映砂砾土静力及液化全过程力学特性的弹塑性本构模型。对比考虑组构演化效应前后砂砾土液化变形、应力路径和超孔隙水压力发展规律,说明了组构演化效应对于模拟砂砾土液化响应的重要影响。通过开展一系列砂砾土静、动力大型三轴试验并结合相关文献试验结果对模型性能进行了验证。结果表明该模型总体上能够合理反映砂砾土在静力排水条件下应力-应变-体变特性以及在液化过程中超孔隙水压力的累积与消散、应力路径演化和液化变形发展情况,可为砂砾土工程数值模拟提供有力的本构工具。

海水干湿循环作用下UHTCC动态压缩性能试验研究

为研究应变率和海水干湿循环周期对超高韧性水泥基复合材料(UHTCC)动态压缩性能的影响,采用直径75 mm的分离式霍普金森压杆系统对0~120 d海水干湿循环作用后的UHTCC试件开展动态压缩试验.通过改进ZWT非线性黏弹性本构模型,提出了一种考虑海水干湿循环作用的UHTCC试件的动态本构模型.结果表明,UHTCC试件的动态抗压强度增强因子随着干湿循环周期的增加逐渐减小.在同一冲击气压下,随着干湿循环周期的增加,UHTCC试件的峰值应力和耗能先增大后减小,并分别在60和90 d时达到峰值.在相同干湿循环周期下,UHTCC试件的峰值应力、动态抗压强度增强因子和耗能均随应变率的增大而增大,表现出明显的应变率效应.改进的动态本构模型能够较好地描述海水干湿循环作用下UHTCC试件的动态压缩应力-应变关系.

Constitutive modelling of composite laminates under uniaxial compression

A nonlinear constitutive model for a single lamina is proposed for the failure analysis of composite laminates. In the material model, both fiber and matrix are assumed to behave elasticplastically and the in-plane shear is assumed to behave nonlinearly with a variable shear parameter.The damage onset for individual lamina is detected by a mixed failure criterion, composed of the Tsai-Wu criterion and the maximum stress criterion. After damage takes place within the lamina,the fiber and in-plane shear are assumed to exhibit brittle behavior, and the matrix is assumed to exhibit degrading behavior. The proposed nonlinear material model is tested against experimental data of composite laminates subjected to uniaxial compressive loads, and good agreement is obtained.

Constitutive model of ferroelectric composites with a viscoelastic and dielectric relaxation matrix Ⅰ——Theory

Based on micromechanics and Laplace transformation, a constitutive model of ferroelectric composites with a linear elastic and linear dielectric matrix is developed and extended to the ferroelectric composites with a viscoelastic and dielectric relaxation matrix. Thus, a constitutive model for ferroelectric composites with a viscoelastic and dielectric relaxation matrix has been set up.

Modeling and mesoscopic damage constitutive relation of brittle short-fiber-reinforced composites

Aimed at brittle composites reinforced by randomly distributed short-fibers with a relatively large aspect ratio, stiffness modulus and strength, a mesoscopic material model was proposed. Based on the statistical description,damage mechanisms, damage-induced anisotropy, damage rate effect and stress redistribution, the constitutive relation were derived. By taking glass fiber reinforced polypropylene polymers as an example, the effect of initial orientation distribution of fibers, damage-induced anisotropy, and damage-rate effect on macro-behaviors of composites were quantitatively analyzed. The theoretical predictions compared favorably with the experimental results.

A dynamic constitutive model of ultra high toughness cementitious composites

In this study,an explicit dynamic constitutive model was established for ultra high toughness cementitious composites(UHTCCs).The model,based on the Holmquist–Johnson–Cook(HJC)model,includes tensile and compressive damage evolution,hydrostatic pressure,strain rate,and the Lode angle effect.The proposed model was embedded in LS-DYNA software and then comprehensive tests were carried on a hexahedral brick element formulation under uniaxial,biaxial,and triaxial stress states to verify its rationality through comparisons with results determined by the HJC and Karagozian&Case(K&C)models.Finally,the proposed model was used to simulate the damage caused to UHTCC targets subjected to blast by embedded explosive and projectile penetration,and predictions were compared with corresponding experimental results.The results of the numerical simulations showed that our proposed model was more accurate than the HJC model in predicting the size of the crater,penetration depth,and the distribution of cracks inside the target following the blast or high-speed impact loading.