A stochastic jump and deterministic dynamics model of impact failure evolution with rate effect

Motivated by the observation of the rate effect on material failure, a model of nonlinear and nonlocal evolution is developed, that includes both stochastic and dynamic effects. In phase space a transitional region prevails, which distinguishes the failure behavior from a globally stable one to that of catastrophic. Several probability functions are found to characterize the distinctive features of evolution due to different degrees of nucleation, growth and coalescence rates. The results may provide a better understanding of material failure

Development of the Molecule Statistical Thermodynamics (MST) Parallel Simulation Package

固体力学的发展逐渐深入到了微纳米尺度，为了研究微纳米尺度材料的力学行为，除了传统的理论分析和实验测量手段外，发展可靠而又高效的计算方法成为了当前微纳米力学研究的热点之一。分子统计热力学方法（Molecule Statistical Thermodynamics，简称MST）是一种新的基于原子表象的分子模拟方法。与传统的基于牛顿运动方程的分子动力学方法（MolecularDynamics，简称MD）相比，MST基于对体系Helmholtz自由能的极小化，适用于分析材料在有限温度下的准静态行为，具有更高的计算效率。本文介绍了MST方法的理论基础，以及由此而开发的MST并行计算软件。在此基础上，采用MST程序模拟了单晶纳米铜体系，显示其计算时间随体系原子数目成线性关系，并对MST并行程序的计算效率进行了讨论

损伤断裂的确定性随机行为和对初始位形的敏感性

我们以恒定载荷下的一排平行纤维或平板试件为原型;考察材料内部的损伤断裂的演化行为.用包含N个键的一维链为模型;模拟这个演化过程(图1).为澄清不同类型的复

损伤断裂图型演化的统计描述

本文采用动力学演化与随机跃迁并存的模型;研究损伤断裂图型的演化规律。根据演化的终态;损伤演化可分为整体稳定(GS)和演化引起剧变(EIC)两种模式;后者联系于断裂现象。本文引入统计描述;并指出;即使微损伤的连接规律是确定性的;无序介质中断裂的出现亦应以概率分布函数描写

从“哥伦比亚”号悲剧看多尺度力学问题

航空航天安全蕴含着大量的涉及多个物理层次的多尺度力学问题.多尺度力学问题对现有的力学概念和理论是一个巨大的挑战.以铝合金层裂和岩石脆性破坏为典型案例,讨论了多尺度力学问题的特点、难点以及可能的处理方法,说明合理表征和处理多尺度问题的跨尺度耦合及跨尺度敏感性是解决多尺度问题的关键

微裂纹串级连接及临界破坏

对一铝合金材料层裂过程的实验研究发现;当损伤累积到一定程度时;受损材料的残余强度突然丧失;表现出临界破坏现象。层裂表面具有分形特征;其分形断面的形成归因于大量微裂纹的串级连接。据此提出了一重正化群弱面模型;并对损伤演化后期的临界破坏现象进行了初步的分析和探讨

Long-Range Stress Redistribution Resulting From Damage in Heterogeneous Media

It has been shown in CA simulations and data analysis of earthquakes that declustered or characteristic large earthquakes may occur with long-range stress redistribution. In order to understand long-range stress redistribution, we propose a linear-elastic but heterogeneous-brittle model. The stress redistribution in the heterogeneous-brittle medium implies a longer-range interaction than that in an elastic medium. Therefore, it is surmised that the longer-range stress redistribution resulting from damage in heterogeneous media may be a plausible mechanism governing main shocks

Self-healing of fractured one dimensional brittle nanostructures

Recent experiments have shown that fractured GaAs nanowires can heal spontaneously inside a transmission electron microscope. Here we perform molecular-dynamics simulations to investigate the atomic mechanism of this self-healing process. As the distance between two fracture surfaces becomes less than 1.0 nm, a strong surface attraction is generated by the electrostatic interaction, which results in Ga–As re-bonding at the fracture site and restoration of the nanowire. The results suggest that self-healing might be prevalent in ultrathin one-dimensional nanostructures under near vacuum conditions

Self-healing in fractured GaAs nanowires

Molecular dynamics simulations are performed to investigate a spontaneous self-healing process in fractured GaAs nanowires with a zinc blende structure. The results show that such self-healing can indeed occur via rebonding of Ga and As atoms across the fracture surfaces, but it can be strongly influenced by several factors, including wire size, number of healing cycles, temperature, fracture morphology, oriented attachment and atomic diffusion. For example, it is found that the self-healing capacity is reduced by 46% as the lateral dimension of the wire increases from 2.3 to 9.2 nm, and by 64% after 24 repeated cycles of fracture and healing. Other factors influencing the self-healing behavior are also discussed

Statistical modeling of damage evolution in spallation

In order to understand the mechanism of the incipient spallation in rolled metals, a one dimensional statistical mode1 on evolution of microcracks in spallation was proposed. The crack length appears to be the fundamental variable in the statistical description. Two dynamic processes, crack nucleation and growth, were involved in the model of damage evolution. A simplified case was examined and preliminary correlation to experimental observations of spallation was made.</span