有机玻璃在高应变率下的损伤型非线性粘弹性本构关系及破坏准则

对两种有机玻璃高应变率下的大变形和破坏行为进行了实验研究,通过改进文献[2]本构关系的非线性弹性项并引入损伤参量,建立了一个适用于更大变形范围、能描述应力平台及本构失稳的损伤型非线性粘弹性本构方程。相应地,从临界损伤量概念出发,提出以应变和应变率为控制变量的破坏准则。不论是本构关系还是破坏准则,理论计算均与试验结果吻合良好。     

有机玻璃在高应变率下的损伤型非线性粘弹性本构关系及破坏准则

对两种有机玻璃高应变率下的大变形和破坏行为进行了实验研究,通过改进文献[2]本构关系的非线性弹性项并引入损伤参量,建立了一个适用于更大变形范围、能描述“应力平台”及“本构失稳”的损伤型非线性粘弹性本构方程。相应地,从临界损伤量概念出发,提出以应变和应变率为控制变量的破坏准则。不论是本构关系还是破坏准则,理论计算均与试验结果吻合良好。     

混凝土黏塑性动力损伤本构关系

从静力弹塑性损伤本构关系的基本框架出发, 综合考虑塑性应变与损伤 演化的率敏感性, 建立了能够较为全面地描述混凝土在动力加载条件下非线性性能的混凝土 黏塑性动力损伤本构模型. 为了考虑塑性应变的率敏感性, 基于Perzyna理论推导了有效应 力空间黏塑性力学基本公式, 采用改进的Perzyna型动力演化方程, 将损伤静力演化方程推 广到动力加载情形. 基于并联弹簧模型, 从概率论的角度推导给出了一维损伤静力演化方程, 并基于能量等效应变的基本概念将其推广到多维损伤演化. 利用数值模拟, 计算得到了 混凝土在不同应变率下的应力应变全曲线, 同时得到了一维动力提高因子和二维动力强度包 络图, 数值结果与试验结果的对比表明了该模型的有效性.     

高应变率下计及损伤演化的材料动态本构行为

材料在高速变形过程中常常伴有不同形式的内部缺陷或微损伤的演化。大量的实验观察表明,损伤演化同时依赖于应变、应变率和温度,而且高应变率和低温之间有某种等价性。由此基于热激活机制,提出了同时依赖于应变率和应变的微损伤演化律,及相应的计及损伤弱化效应的率型本构关系。以聚丙烯/尼龙（PP/PA）共混高聚物为例,具体研究了其计及损伤演化的ZWT本构关系,并区分其率相关的本构响应及率相关的损伤演化响应。     

混凝土单轴受拉的非局部本构模型

混凝土受拉本构行为存在很强的局部软化现象,使得单轴受拉试验无法给出应力-应变关系,而只能给出应力-位移关系。本文根据内变量理论和等效应变假设建立了基于真实应变的混凝土单轴受力本构方程,并根据Weibull分布可以描述混凝土等脆性材料断裂过程的试验现象,建立了关于弹性应变的损伤演化规律。然后,通过假设平均应变与真实弹性应变的函数关系,在应力-平均应变的本构关系中采用平均弹性应变以描述其非局部行为,而在材料的损伤演化规律中采用真实弹性应变以描述其局部行为,由此建立了单轴受拉荷载条件下的非局部本构模型。最后,对一个单调受拉试验和一个反复受拉试验的仿真结果表明所提出的非局部本构模型可以准确地模拟试验结果。     

内爆炸加载条件下圆筒的膨胀、破裂规律研究

以经典热粘塑性本构关系 (John Cook本构关系和Powerlaw本构关系 )为基础 ,建立了更适当表征材料特征的新的、解耦的本构关系。采用SHPB(分离式霍普金森杆 )技术测定了常用弹箭材料 35CrMnSiA的不同应变率下的应力、应变关系 ,并采用拟合的方法确定了本构方程中的材料常数。与高速摄影技术测得的径向位移函数及圆筒材料的损伤演化方程相结合 ,建立了控制内爆炸加载圆筒膨胀 ,直至破裂的完备方程组 ,完成了内爆炸加载圆筒问题的数值模拟 ,计算结果与以往有关箭弹材料圆筒膨胀的实验结果符合较好。     

热粘塑性体的积分－微分型本构关系

应用　　　关于应力是五维偏应变空间变形历史的泛函的概念和Ｖａｌａｎｉｓ有关内＊时理论的描述，本文提出，对热粘塑性体，应力可设为应变、应变率和温度历史的泛函；并应用Ｍｉｌｌｅｒ和其它一些作者有关内变量演化方程的描述，由此建立了热粘塑性体的积分－微分到本构方程．这一积分－微分型本构关系大体和Ｍｉｌｌｅｒ微分型模型等价．对１０２０钢的单轴本构响应进行了数值模拟，和Ｔａｎａｋａ与Ｍｉｌｌｅｒ的分析及一些实验结果符合较好．     

热粘塑性体的积分—微分型本构关系

应用ИЛЪЮШИН关于应力是五维偏应变空间变形历史的泛函的概念和Ｖａｌａｎｉｓ有关内时理论的描述，本文提出，对热粘塑性体，应力可设为应变、应变率和温度历史泛；并应用Ｍｉｌｌｅｒ和其它一些作者有关内变量演化方程的描述，由此建立了热粘塑性体的积分－微分型本构方程这一积分－微分型本构关系大体和Ｍｉｌｌｅｒ微分型模型等价。对１０２０钢的单轴本构响应进行了数值模拟，和Ｔａｎａｋａ与Ｍｉｌｌｅｒ的分析及一些实     

考虑损伤的弹—粘塑性本构方程

采用Ｐｅｒｚｙｎａ过应力本构框架，引入塑性损伤在饱和强化率相关介质中的动态演化规律，建立了考虑损伤的弹－粘塑性本构方程，修正了Ｅｆｔｉｓ等人将Ｐｅｒｚｙｎａ方程推广时采用不一致的基体强化模式推演损伤演化方程和本构关系这一矛盾。详细计算了黄铜的初始屈服强度及率相关屈了面，给出了动态单轴拉伸数值结果并与实验进行了比较，结果符合很好。     

真三轴应力状态下岩石损伤本构模型

从岩石微元破坏服从Weibull 随机分布的特点出发,建立了真三轴应力状态下岩石损伤软化统计本构关系;根据应力应变关系的几何条件,建立了本构模型参数与岩石变形过程中应力应变曲线特征参量的理论关系,从而增强了模型的适应性;最后通过试验实测数据验证了模型的合理性.     

A void nucleation and growth based damage framework to model failure initiation ahead of a sharp notch in irradiated bcc materials

A continuum damage framework is developed and coupled with an existing crystal plasticity framework, to model failure initiation in irradiated bcc polycrystalline materials at intermediate temperatures. Constitutive equations for vacancy generation due to inelastic deformation, void nucleation due to vacancy condensation, and diffusion-assisted void growth are developed. The framework is used to simulate failure initiation at dislocation channel interfaces and grain boundaries ahead of a sharp notch. Evolution of the microstructure is considered in terms of the evolution of inelastic deformation, vacancy concentration, and void number density and radius. Evolution of the damage, i.e., volume fraction of the voids, is studied as a function of applied deformation. Effects of strain rate and temperature on failure initiation are also studied. The framework is used to compute the fracture toughness of irradiated specimens for various loading histories and notch geometries. Crack growth resistance of the irradiated specimens are computed and compared to that of virgin specimens. Results are compared to available experimental data.     

The evolution of voids in the plasticity strain hardening gradient materials

The main aim of this paper is to opens out the meso-mechanism of void growth and coalescence in the matrix materials with graded strain-hardening exponent distribution. For this end, detailed finite element computations of a representative cylindrical cell containing a spherical void have been carried out. According to the FE analyses, significant effects of the strain-hardening exponent gradient (SEG) in the matrix on the void growth and coalescence are revealed: (1) In the homogeneous materials, the void growth and coalescence are slightly dependent on the strain-hardening exponent, however, the SEG distribution in the matrix can increase remarkably the void growth rate and decrease seriously the void coalescence strain. (2) The critical void shapes in the homogeneous materials are mainly governed by the macroscopic stress triaxiality, but due to earlier plastic flow localization in the softer matrix layer, the SEG distribution in the matrix has very significant effects on the deformed void shapes, especially when the stress triaxiality is lower. (3) When the triaxial stress levels are lower, in the homogeneous materials, the shape change mode of the void evolution is dominate so the void growth rate is very low; however, the SEG distribution in the matrix can bring the volume change mode out, as a result of increasing the void growth rate. (4) Comparisons of the numerical results with the existing damage model indicate that the classic damage model cannot give satisfying prediction to the void growth in both the homogeneous strain-hardening matrix and the SEG materials. On the basis of large numbers of numerical computations, a new damage model, which can uniformly describe the void growing in the homogeneous and plasticity gradient materials, is suggested. A mass of element computations have validated that the new damage model can give satisfying agreement with the FE results of cell model.     

Effect of stress triaxiality on porosity evolution in notched bars: Quantitative agreement between a recent dilatational model and X-ray tomography data

In this paper, it is shown that a micromechanically motivated macroscopic model can predict with accuracy the role of the stress state on void evolution in engineering materials. Specifically, a recent criterion that accounts for the influence of all stress invariants on the dilatational response of porous metals is used to predict porosity evolution and strength reduction in aluminum alloy AA 6016-T4. A very good quantitative agreement between the simulation results and X-ray tomography damage measurements in specimens of different notch acuities is obtained. In contrast to existing models, the void volume fraction evolution correlates very well with the X-ray data for all stress triaxialities.     

伴随微孔洞生长的裂纹弹塑性定常扩展

裂纹在韧性材料中扩展时,将们随着微孔洞的萌生和生长,孔洞的萌生和深化将直接影响着材料的总体断裂韧性和强度,以往的研究主要集中在将裂纹的扩展刻划为微孔洞的萌生、生长和汇合这样一个过程。从传统的断裂过程区模型出发研究微孔洞的萌生和生长对材料总体断裂韧性的影响,通过采用Ｇｕｒｓｏｎ模型,建立塑性增量本构关系,然后针对定常扩展情况直接进行分析,孔洞对材料断裂韧性的影响由本构关系刻划,而在孔洞汇合模型中,上     

微孔洞生长对板材拉伸过程中变形局部化的影响

本文在作者提出的含孔洞材料下限本构方程的基础上，采用了初始缺陷带模型对微孔洞生长及分布对板材拉伸过程中变形局部影响进行了，分析着重研究了细观损演化规律对变形局部化模式及临界应变的影响，并成功预测了ＡＩＳＩ４３４０钢板材拉伸试件变形局部化换稳为及失稳方向。     

A self-consistent analysis for coupled elastoplastic damage problems

Based on irreversible thermodynamics and internal state variable theory, the volume-averaged Clausius-Duhem inequality is presented. In contrast to former investigations on damage-elastoplasticity, our evalustions are founded on the volume-averaged field equations of the analyzed elements and the self-consistent method. Hence, our results not only include the influence of void shapes but also consider the interaction among voids. Further, previous work about coupled elastoplastic damage problems only takes into account small initial void volume fractions. Our work, however, will be able to deal with elastoplastic damage problems with larger initial void volume fractions. Project supported by the National Natural Science Foundation of China (19762002) and Natural Science Foundation of Jiangxi in China     

基于M积分的脆性材料微缺陷等效损伤面积/体积表征

随着脆性材料在工程中的广泛应用,对脆性材料中微缺陷进行统一的损伤水平标定,具有重要的科学研究和工程应用价值. 本研究提出一种基于M积分的材料等效损伤面积/体积标定方法, 以具有相同M积分值的圆孔面积或球孔体积来标定 复杂微缺陷构型的损伤水平,从而实现不同类型微缺陷真实损伤水平的统一表征. 首先,基于Lagrangian能量密度函数推导 了M积分定义式,并简述了M积分的物理意义,基于域积分方法实现二维/三维M积分的数值计算. 随后,提出了基 于M积分的材料缺陷等效损伤面积/体积标定方法,以圆孔面积/球孔体积来标定复杂微缺陷材料系统的损伤水平. 最后, 针对单轴拉伸载荷作用下的二维/三维脆性体含不同缺陷构型,具体计算了椭圆孔、裂纹以及双裂纹、双孔洞、裂纹和孔洞干 涉等复杂缺陷构型情况下的等效损伤面积/体积,并详细分析了缺陷之间的干涉效应及影响因素. 本研究旨在基于M积分等 效方法量化脆性材料中各类微缺陷造成的损伤程度,实现损伤等级标定,有益于工程材料及结构的损伤容限设计及完整性评估.      

A microscopic damage model considering the change of void shape and application in the void closing

A microscopic damage model of ellipsoidal body containing ellipsoidal void for nonlinear matrix materials is developed under a particular coordinate. The change of void shape is considered in this model. The viscous restrained equation obtained from the model is affected by stress ∑_(ij), void volume fraction f, material strain rate exponent m as well as the void shape. Gurson's equation is modified from the numerical solution. The modified equation is suitable for the case of nonlinear matrix materials and changeable voids. Lastly, the model is used to analyze the closing process of voids.     

Volume-weighted mixture theory for granular materials

In the present work we treat granular materials as mixtures composed of a solid and a surrounding void continuum, proposing then a continuum thermodynamic theory for it. In contrast to the common mass-weighted balance equations of mass, momentum, energy and entropy for mixtures, the volume-weighted balance equations and the associated jump conditions of the corresponding physical quantities are derived in terms of volume-weighted field quantities here. The evolution equations of volume fractions, volume-weighted velocity, energy, and entropy are presented and explained in detail. By virtue of the second law of thermodynamics, three dissipative mechanisms are considered which are specialized for a simple set of linear constitutive equations. The derived theory is applied to the analysis of reversible and irreversible compaction of cohesionless granular particles when a vertical oscillation is exerted on the system. In this analysis, a hypothesis for the existence of a characteristic depth within the granular material in its closely compacted state is proposed to model the reversible compaction.