孔洞材料动态破碎的细观机理

采用Ｃ－Ｈ－Ｊ动态微孔长大细观模型研究孔洞材料中的动态破碎的细观机理，导出了微孔动态演化方程及动态破碎尺寸与材料孔隙度的关系，利用本文给出的动态破碎的细观机制可对破甲弹的破甲机理给出合理的解释。     

金属材料动态延性损伤的细观描述

本文系统地回顾了高加载率下金属材料延性损伤的细观研究现状,对现有的各种动态延性损伤模型进行了评述。针对现有的工作所存在的问题,指出了今后这些方面有潜力的研究方向。     

塑性损伤的发展与应用

本文介绍了塑性损伤的机制和建立塑性损伤模型的一般方法;系统地分析比较了基于连续介质力学、细观力学、连续损伤力学等多种损伤理论,推导了它们之间的内在联系;综述了三轴度、应变路径、组织等对塑性损伤的影响,重点阐述了损伤-塑性流变的耦合分析;还介绍了电阻测量、统计与定量表征、有限元等塑性损伤的分析方法;并且分析了目前塑性损伤...     

混凝土材料的粘塑性损伤统一本构模型

发展了只适用于金属类材料的粘塑性统一本构理论,借助经典塑性理论的基本法则,建立了无屈服面和无破坏面的混凝土材料的粘塑性损伤统一本构模型。放弃了传统统一本构模型的静水压不影响非弹性变形和无非弹性体积膨胀的基本假设;发展了间断的经典塑性乘子,使其为连续函数,并提出了相应的构造方法,拓展定义了其物理意义。数值模拟显示,此本构模型能够模拟混凝土材料的率相关性质、在压缩载荷作用下的体积膨胀现象和由损伤引起的应力软化和刚度退化现象。     

颗粒增强复合材料刚塑性细观损伤本构模型的验证

验证已建立的刚性颗粒增强复合材料刚塑性细观损伤本构理论的合理性和可靠性。将上述本构理论的数值计算结果与SiC颗粒增强的铝基复合材料单轴拉伸实验结果进行比较。结果表明:由此本构模型得到的应力-应变理论曲线与拉伸实验所得的应力-应变曲线基本吻合,从而验证了该本构模型的合理性和可靠性。因此已建立的刚塑性细观损伤本构模型可用于数值计算,在一定程度上可预测颗粒增强复合材料的力学特性。在此基础上对大、小颗粒增强复合材料的延展性、空洞和颗粒体积分数演化规律等作了讨论。      

硬聚氯乙烯的粘塑性本构模型与裂纹扩展行为

建立材料的粘塑性本构模型,进行粘塑性裂纹扩展试验,是开展聚合物粘塑性裂纹扩展问题研究的基础.采用恒定应变速率的方法,对硬聚氯乙烯进行低应变速率下的拉伸试验,确定各应变速率下应力与应变的关系曲线.实验数据表明,该材料的力学性能对应变速率有依赖性,与时间相关,是典型的粘塑性材料.根据实验测得的不同应变速率下应力-应变关系的曲线族,对实验数据进行多元回归分析,确定有关的材料常数,建立了硬聚氯乙烯材料Bailey-Norton公式形式的粘塑性本构模型.进行硬聚氯乙烯的粘塑性裂纹扩展试验研究,得到了裂纹长度增量与时间的关系.     

海冰的粘塑性蠕变模型

本文将粘塑性理论用于海冰荷载分析,并将现有的一维蠕变方程推广到二维形式,采用非线性有限元方法计算了作用在一单桩结构上的最大静冰力。     

深开挖中粘弹—粘塑性土体稳定的数值分析

本文探讨软土地基中喷锚网支护开挖性能粘弹－粘塑性有限元分析方法，采用西源流变模型编制了模拟基坑开挖全过程的有限元程序，并对实际工程进行了分析。     

金属基复合材料细观损伤机制与宏观性质关系的研究

通过将作者发展的广义自洽有限元迭代平均化方法同用于描述金属塑性损伤的Gurson本构模型相结合, 对SiC 增强A l₅₄₅₆的细观损伤机制与其宏观性质的关系进行了参数研究。金属基体的细观损伤机制包括两种形式, 增强相与金属基体之间界面的脱开及基体内孔洞的成核、长大与汇合。结果表明, 界面的脱开增大了金属基复合材料的塑性, 但导致了增强相增强作用的降低。      

延性材料动态破碎机理及初始损伤效应

运用Ｐｅｒｚｙｎａ的粘塑性过应力本构模型，分析了延性材料动态破碎的细观机理，给出了破碎尺寸与材料孔隙度的关系。此外。研究了初始损伤度对材料动态碎的是影响。结果表明，在初始损伤较小时，破碎尺寸随机隙度增加而减小；而当初始损伤较大时，破碎尺寸随孔隙度增加而增大。这反映出材料的破碎是一个时间盯关过程或累积过程。     

An Endochronic Viscoplastic Approach for Materials with Different Behavior in Tension and Compression

To describe viscoplastic materials with different behavior intension and compression via the example of filled PTFE(Polytetrafluorethylen), an endochronic viscoplastic materialmodel is proposed. The approach is based on a rheological modelwithout an elastic range, using a rate-independent elastoplasticelement with an endochronic flow rule and a nonlinear elastic lawin parallel connection with a nonlinear Maxwell model. The SDE(strength differential effect) due to different experimentalresults in tension and compression tests is described by twointernal variables and their evolution equations. Numericalsimulations show that the model can describe the short and longtime material behavior of filled PTFE under isothermal loading inboth, tension and compression.     

A CDM Approach of Ductile Damage with Plastic Compressibility

The paper proposes a modified formalism of continuum damage mechanics in order to describe plastic compressibility in the context of ductile damage. The model uses two damage state variables, one of them playing role of porosity in micromechanics based approaches like Gurson’s model. Various versions of the model are determined and compared with Gurson’s model, in terms of the constitutive responses for various loading conditions, as well as for simple structural examples like a free and a clamped plate under plane strain, and an axisymmetric notched bar under tension. The classical CDM is also applied and some advantages of the proposed approach are underlined.     

等温淬火球墨铸铁滚动磨损与损伤性能

利用不同热处理方式和球化工艺,获得两种显微组织和不同硬度的等温淬火球墨铸铁(Austempered Ductile Iron,ADI)材料,利用MMS-2A微机控制摩擦磨损试验机对比研究了两种等温淬火球墨铸铁材料、车轮材料与U71Mn钢轨匹配时的滚动磨损与损伤性能。结果表明:ADI材料与U71Mn钢轨匹配时的摩擦因数明显小于车轮材料;由于ADI材料具有自润滑效果导致其磨损率明显小于车轮材料,ADI材料的自润滑性能也降低了对摩副U71Mn钢轨的磨损率,其中含有较大球状石墨和较少残余奥氏体的ADI2材料和对摩副U71Mn钢轨的磨损率最小;ADI材料的磨损机制主要表现为轻微疲劳磨损,对摩副U71Mn钢轨的磨损机制主要表现为黏着和轻微疲劳磨损,而轮轨材料匹配时的塑性流动层显著,损伤以表面疲劳裂纹和剥层损伤为主。     

The Influence of a Surface Coating on the High-rate Fragmentation of a Ductile Material

A bifurcation analysis of a layered ductile structural element undergoing homogeneous, high-rate extension is presented. Formation of multiple strain localization sites provides a precursor to ductile fragmentation, and the objective of the analysis is to investigate the effect of an added surface layer on resistance of the structural element to fragmentation. The analysis shows that, in addition to dissipating plastic work, the outer layer can increase the total energy dissipation prior to fragmentation by increasing bifurcation strain. The analysis also shows that the strain hardening exponent of the outer layer plays an important role in increasing the bifurcation strain; higher values of hardening exponent result in higher bifurcation strain. Strength and density of the outer layer play a secondary role in increasing bifurcation strain. Once a material with a high hardening exponent is chosen for the outer material, its strength plays an important role in increasing the total dissipated energy. The analysis also reveals that, for certain combinations of strength and hardening exponent of the outer layer, the sandwich structure can dissipate more energy than a homogeneous core structure of the same total thickness and length. This is so even when the outer layer is weaker than the core. Energy dissipated per unit mass can be significantly improved by choosing a softer outer layer which displays high-strain hardening. Thus, the bifurcation analysis presented here provides a quantitative guideline for material selection in designing layered structures optimized for resistance to fragmentation.     

Damage analysis of laminated composites using a new coupled micro‐meso approach

In this study, the simplicity and strong physical meaning of micromechanics approach and capability of mesomechanics approach for damage analysis of structures with complex loadings are employed to develop a new micro‐meso approach. For this purpose, a new micromechanics model is developed to predict the matrix cracking initiation and evolution in laminated composites. These damage initiation and evolution are replaced with the damage criteria and flow rule in the continuum damage approach, respectively. The results of this procedure are used in the FEM damage analyses of laminated composites to predict constitutive response of layered composites. It is shown that, the predicted stress distribution and strain energy in a lamina unit cell are in good agreement with the finite element results. Furthermore, it is shown that the predicted stress–strain behaviours are in good agreement with the available experimental results for various laminates with different lay‐ups.