纤维增强复合材料的破坏机理

纤维增强复合材料本身是一个非均匀各向异性力学结构。复合材料的研制、设计和使用都与力学密切相关。复合材料的破坏机理比金属材料复杂,不同组分的构成使其在加工中存在和使用中带来的缺陷比金属多。它的破坏机理与纤维、基体组分的性能,粘结强度,纤维铺设方向和顺序,工作条件等有关。需要采用有效的试验和分析方法,研究复合材料在不同      

纤维增强复合材料疲劳研究现状和发展

纤维增强复合材料的疲劳研究是一个很活跃的领域。本文根据近20年来国内外有关复合材料疲劳研究的论文和报告,综述了当前研究的四个方面问题:①复合材料疲劳性能研究及其影响因素;②疲劳损伤的形成和裂纹扩展;③疲劳损伤模型;④疲劳寿命估算。笔者还对当前复合材料疲劳研究的发展表述了己见。      

THE NEW CRITERIA OF ELASTIC AND FATIGUE FAILURE IN THE COMPONENT OF COMPLEX STRESS STATES

In this paper, a total criterion on elastic and fatigue failure in complex stress, that is, octahedral stress strength theory on dynamic and static states on the basis of studying modern and classic strength theories. At the same time, an analysis of an independent and fairly comprehensive theoretical system is set up. It gives generalized failure factor by 36 materials and computative theory of the 11 states of complex stresses on a point, and derives the operator equation on generalized allowable strength and a computative method for a total equation can be applied to dynamic and static states. It is illustrated that the method has a good exactness through computation of eight examples of engineering. Therefore, the author suggests applying it to engineering widely.     

An analysis of the shear failure of rigid-linear hardening beams under impulsive loading

A theoretical rigid-plastic analysis for the dynamic shear failure of beams under impulsive loading is presented when using a travelling plastic shear hinge model which takes into account material strain hardening. The maximum dynamic shear strain and shear strain-rate can be predicted in addition to the permanent transverse deflections and other parameters. The conditions for the three modes of shear failure, i.e., excess deflection failure, excess shear strain failure and adiabatic shear failure are analyzed. The special case of an infinitesimally small plastic zone is discussed and compared with Nonaka's solution for a rigid, perfectly plastic material. The results can also be generalized to examine the dynamic response of fibre-reinforced beams.     

脆性陶瓷靶高速侵彻/穿甲动力学的研究进展

近10年来, 有关陶瓷的材料特性和陶瓷及陶瓷复合靶的高速侵彻$\!/\!$穿甲动力学研究已成为国际冲击工程界的热点研究领域. 相关研究有着现实的军事需求和应用背景. 国内在该领域的研究工作相对较少. 本文着重给出陶瓷及陶瓷复合靶高速侵彻$\!/\!$穿甲动力学的国外研究现状.对陶瓷及陶瓷复合靶高速侵彻$\!/\!$穿甲的实验方法、作用机理和理论模型等进行综述, 介绍空腔膨胀模型在陶瓷侵彻力学中的应用以及脆性材料高速侵彻效应中的失效波效应. 文章最后给出近期可开展的工作建议.      

基于空间应用环境的光纤陀螺可靠性分析

根据光纤陀螺应用于空间应具有长寿命高可靠性的要求,对空间应用环境进行了分析,结合空间应用的环境,采用故障树分析的方法对数字闭环干涉式光纤陀螺进行了可靠性分析.根据可靠性分析的结果,找出了光纤陀螺的薄弱环节,并对重要且出现故障概率大的器件如光源和光纤环的故障机理进行了分析,提出了改进设计措施,并已应用在光纤陀螺产品的设计中.     

PROGRESSIVE FRACTURE MODELING OF THE FAILURE WAVE IN IMPACTED GLASS

The failure wave has been observed propagating in glass under impact loading since 1991. It is a continuous fracture zone which may be associated with the damage accumulation process during the propagation of shock waves. A progressive fracture model was proposed to describe the failure wave formation and propagation in shocked glass considering its heterogeneous meso-structures. The original and nucleated microcracks will expand along the pores and other defects with concomitant dilation when shock loading is below the Hugoniot Elastic Limit. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from the collapse of the original pores. Numerical simulation of the free surface velocity was performed and found in good agreement with planar impact experiments on K9 glass at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.     

FRP-混凝土界面剥离破坏过程并行数值模拟

采用材料真实破裂过程三维并行分析(RFPA~(3D)-Parallel)系统,对FRP-混凝土界面的粘结性能进行了三维并行数值试验研究,数值试验再现了FRP-混凝土构件的三维破裂过程演化过程,清晰地表明拉伸载荷作用下FRP-混凝土界面剥离破坏是一个细观损伤不断产生和宏观裂缝形成的渐进过程,FRP-混凝土结构损伤演化过程的声发射揭示了FRP-混凝土结构在外载荷作用下的损伤程度.FRP-混凝土结构在加载过程中的变形剥离破坏过程大致可以划分为弹性变形阶段、弹性软化阶段、弹性软化剥离阶段和软化剥离阶段.数值计算表明RFPA~(3DParallel并行数值模拟方法为FRP-混凝土结构界面剥离破坏过程和机理研究提供了一个很好的途径,同时也为研究FRP-混凝土工程结构等的损伤断裂机理提供了一个新的分析手段.     

5083H111铝合金宽应变率拉伸动态本构模型

结合5083H111铝合金较宽应变率范围2×10-4~4×102 s-1内的拉伸实验数据,揭示该铝合金的拉伸“V”型率效应特征,分析对数应变率敏感系数λ和切线模量E1的应变率和应变相关性,进而通过对Johnson-Cook模型的修正来建立合理描述5083H111铝合金较宽应变率范围内力学行为的动态拉伸本构模型.建立的动态本构模型中,流动应力包括应变率相关和应变相关两部分.该模型合理描述了5083H111铝合金的拉伸“V”型率效应特征,预测结果与实验结果较为一致.另外,结合破坏应变的对数应变率敏感系数β,得到了拉伸破坏应变预测方程,其预测结果也与实验结果基本一致.     

FIRST-PASSAGE FAILURE OF PREISACH HYSTERETIC SYSTEMS

The first-passage failure of a single-degree-of-freedom hysteretic system with non- local memory is investigated. The hysteretic behavior is described through a Preisach model with excitation selected as Gaussian white noise. First, the equivalent nonlinear non-hysteretic sys- tem with amplitude-dependent damping and stiffness coefficients is derived through generalized harmonic balance technique. Then, equivalent damping and stiffness coefficients are expressed as functions of system energy by using the relation of amplitude to system energy. The stochastic aver- aging of energy envelope is adopted to accept the averaged It5 stochastic differential equation with respect to system energy. The establishing and solving of the associated backward Kolmogorov equation yields the reliability function and probability density of first-passage time. The effects of system parameters on first-passage failure are investigated concisely and validated through Monte Carlo simulation.