带裂纹的椭圆孔口问题的应力分析

断裂现象与材料和结构中的孔洞、缺口或裂纹等缺陷密切相关,这是因为缺陷附近的应力集中明显.该文利用复变方法,通过保角映射研究了带裂纹的椭圆孔洞的平面弹性问题,给出了应力强度因子的解析解.并由此计算了两互相垂直的裂纹问题.     

应用数字图像相关方法测量含缺陷试样的全场变形

利用数字图像相关方法测量表面带孔洞、裂纹、缺口等缺陷试样的全场变形是许多实际测量任务中经常遇到的问题.就此问题,本文阐述了一种先对要避免计算的缺陷区域进行标记,在随后进行的相关计算中直接避免这些标记区域的方法.在已计算得到全场位移的情况下,文中提出了基于局部位移场最小二乘拟合的方法来计算区域边界、孔洞、裂纹或缺口附近等区域应变.最后对单侧边带半圆缺口试样的单向疲劳拉伸实验的计算结果充分显示本文方法的有效性和可靠性.     

缺口疲劳裂纹形成的J积分分析

进行了循环载荷的缺口顶端局部应变和形变功密度的循环J 积分分析和实验标定,证实:缺口顶端形变功密度依赖于循环J 积分和缺口半径ρ之比,即:△J/ρ=α_c△W_0通过对缺口疲劳裂纹形成过程的分析,并依据上述关系和光滑试样应变疲劳关系N_(?)(△W)~(?)=c,提出了予测缺口疲劳裂纹形成寿命的公式:N_i(△J/α_cρ)~β=c_n进行了各种缺口试样,在各种载荷条件的疲劳裂纹形成实验,结果证明,对不同应力比R 的载荷,在各种形变程度:从线弹性至全面屈服,疲劳裂纹形成寿命N_i 和△J/α_cρ均满足此关系式.分析比较了△J/α_cρ和缺口疲劳领域的另两个常用参量△K/ρ~(1/2)和1/2△ε之间的关系,△J/α_cρ较后两者有更广泛的适用性.     

孔洞裂纹问题的一种数值方法

研究孔洞与裂纹的相互作用问题,通过把适于单一裂纹的Bueckner原理扩充到含有多孔洞多裂纹的一般体系,将原问题分解为承受远处载荷不含裂纹不含孔洞的均匀问题,和在远处不承受载荷但在裂纹面上和孔洞表面上承受面力的多孔洞多裂纹问题.于是,以应力强度因子作为参量的问题可以通过考虑后者来解决,而利用笔者提出的杂交位移不连续法,这种多孔洞多裂纹问题是容易数值求解的.算例说明该数值方法对分析平面弹性介质中孔洞与裂纹的相互作用既简单又有效.     

应用数字图像相关方法测量含缺陷试样的全场变形

利用数字图像相关方法测量表面带孔洞、裂纹、缺口等缺陷试样的全场变形是许多实际测量任务中经常遇到的问题。就此问题，本文阐述了一种先对要避免计算的缺陷区域进行标记，在随后进行的相关计算中直接避免这些标记区域的方法。在已计算得到全场位移的情况下，文中提出了基于局部位移场最小二乘拟合的方法来计算区域边界、孔洞、裂纹或缺口附近等区域应变。最后对单侧边带半圆缺口试样的单向疲劳拉伸实验的计算结果充分显示本文方法的有效性和可靠性。     

平面弹性介质多孔多裂纹问题的一种数值方法

提出了平面弹性介质中多孔洞多裂纹相互作用问题的一种数值计算方 法. 通过把适于单一裂纹的Bueckner原理扩充到含有多孔洞多裂纹的一般体系，将原问题 分解为承受远处载荷不含裂纹不含孔洞的均匀问题，和在远处不承受载荷但在裂纹面上和孔 洞表面上承受面力的多孔洞多裂纹问题. 于是，以应力强度因子作为参量的问题可以通过考 虑后者(多孔洞多裂纹问题)来解决，而利用提出的杂交位移不连续法，这种多孔 洞多裂纹问题是容易数值求解的. 算例说明该数值方法对分析平面弹性介质中多孔洞多裂纹 相互作用的问题既简单又有效.     

J积分方法预测缺口疲劳裂纹形成的研究

对承受循环载荷的缺口试样,其缺口顶端形变功密度依赖于循环J积分和缺口半径ρ之比,即:△J=α_cρ△W_0依据缺口疲劳裂纹形成过程及光滑试样应变疲劳的形变功密度与疲劳寿命的关系N_f(△W)~r=C,导出并由实验证实了缺口疲劳裂纹形成寿命的预测公式:N_i(△J/α_cρ)~β=C_n。根据这一关系式,可以较准确地预测大范围屈服及全面屈服条件下缺口疲劳裂纹形成寿命。     

缺口短疲劳裂纹扩展的弹塑性断裂力学

前言缺口试件疲劳有许多不同于光滑试件疲劳的特征,其中最主要的就表现在疲劳裂纹扩展方面.在循环载荷作用下,缺口试件应变分布是不均匀的,缺口顶端往往存在一循环塑性应变区,在其周围是弹性应变区.一般来说,微裂纹在缺口顶端形成;其Ⅰ阶段传播周次很短,缺口试件疲劳寿命主要由短裂纹在缺口塑性应变区传播周次及裂纹在弹性应变区传播周次两部分组成.短裂 ...     

韧性断裂裂纹尖端的物理特征和力学行为

本文综述了金属材料发生韧性断裂的裂尖钝化,孔洞成核和长大,孔洞-孔洞或孔洞-裂尖汇合导致裂纹扩展的物理特征,和描述这些特征的本构理论及物理模型。      

CRACK INTERACTING WITH AN INDIVIDUAL INCLUSION BY THE FRACTURE CRITERION OF CONFIGURATIONAL FORCE

基于构型力概念提出一种可判断裂纹起裂以及裂纹扩展方向的新断裂准则.该准则假设当构型合力值达到一个临界值时裂纹开始扩展,而裂纹扩展的方向则为构型合力的矢量方向.基于此断裂准则,本文开发构型力的有限元计算方法,实现对裂纹扩展的数值模拟,并着重对工程中常见的含孔洞/夹杂结构的裂纹扩展问题展开研究.研究结果表明,基于构型力的裂纹扩展准则可以很好地预测裂纹与孔/夹杂的干涉作用,其数值模拟结果与实验结果相符,从而验证了该裂纹扩展模拟方法的有效性.通过对裂纹和夹杂（圆孔、软夹杂、硬夹杂）干涉问题的数值模拟表明,裂纹前端夹杂对裂纹的扩展具有重要影响.裂纹的扩展方向与裂纹和夹杂的相对位置、以及夹杂类型密切相关.软夹杂和圆孔会吸引裂纹向其扩展,而硬夹杂会排斥裂纹扩展,裂纹在扩展过程中会绕开硬夹杂.当裂纹与夹杂夹角较小时,夹杂对裂纹扩展的影响作用明显,当夹角较大时,夹杂对裂纹扩展的影响较小;特别当裂纹与夹杂夹角为45°时,软夹杂和圆孔可能会抑制裂纹的扩展,使裂纹扩展发生止裂.研究结果有助于认清含孔洞/夹杂结构中的裂纹扩展或止裂问题,对于工程中的断裂问题具有重要指导意义.     

缝水压力和裂缝面接触条件对重力坝裂缝扩展影响

基于多边形比例边界有限元模拟了重力坝裂缝扩展过程,综合考虑了坝-库水-地基相互作用、裂缝面接触和缝水压力的影响。其中该接触模型能够有效防止裂缝面的相互嵌入;该缝水模型除能考虑裂缝面开合速度、缝隙宽度和水流形态对缝水压力分布的影响,还可基于连续性条件模拟缝内水体流动和空化的现象。以Koyna坝裂缝扩展为例,研究了裂缝面接触条件和缝水压力对计算结果的影响。结果显示,考虑接触的影响,震损较为严重。而与假定为常水压力分布的情况相比,实际的缝水压力分布形式对结果影响较为复杂。在裂缝张开时,减小了裂缝扩展的可能,而在裂缝闭合时正好与之相反。     

三维冲击荷载弹塑性弯曲裂纹张开位移

主要研究冲击载荷作用下的三维弹塑性弯曲裂纹尖端的张开位移问题．综合考虑了冲击作用应力,三维塑性区域边界上正应力与剪应力,利用二阶摄动方法计算了三维弹塑性弯曲裂纹尖端的张开位移．用数值解法计算出三维弹塑性弯曲裂纹尖端张开位移,作图分析了三维弹塑性弯曲裂纹尖端张开位移与三维裂纹体几何尺寸之间的变化关系．三维弹塑性弯曲裂纹尖端张开位移随着三维裂纹体厚度的增大而减小,随着三维裂纹体厚度的均匀增大,三维弹塑性弯曲裂纹尖端张开位移尺寸不断减小,减小的幅度越来越小,最终趋于平面应变状态下的弹塑性弯曲裂纹尖端张开位移尺寸．当三维裂纹体几何尺寸相同时,三维弯曲裂纹尖端动态张开位移随外部冲击载荷的不断增大而逐渐增大,三维弯曲裂纹尖端动态张开位移随动荷系数的增大而迅速增大,建立了一个计算三维弹塑性弯曲裂纹尖端动态张开位移的崭新理论模型．     

Coupled modeling of damage growth and permeability variation in brittle rocks

This paper presents a coupled model for anisotropic damage and permeability evolution by using a micro–macro approach. The damage state is represented by a second order tensor. The evolution of damage is determined from a crack propagation criterion. The free enthalpy function of cracked material is obtained by using micromechanical considerations. It is assumed that cracks exhibit normal aperture which is coupled with the crack growth due to asperities of crack faces. By using Darcy’s law for macroscopic fluid flow and assuming laminar flow in microcracks, the overall permeability of the RVE is obtained by a volume averaging procedure taking into account crack aperture in each orientation.     

Intergranular strain evolution near fatigue crack tips in polycrystalline metals

The deformation field near a steady fatigue crack includes a plastic zone in front of the crack tip and a plastic wake behind it, and the magnitude, distribution, and history of the residual strain along the crack path depend on the stress multiaxiality, material properties, and history of stress intensity factor and crack growth rate. An in situ, full-field, non-destructive measurement of lattice strain (which relies on the intergranular interactions of the inhomogeneous deformation fields in neighboring grains) by neutron diffraction techniques has been performed for the fatigue test of a Ni-based superalloy compact tension specimen. These microscopic grain level measurements provided unprecedented information on the fatigue growth mechanisms. A two-scale model is developed to predict the lattice strain evolution near fatigue crack tips in polycrystalline materials. An irreversible, hysteretic cohesive interface model is adopted to simulate a steady fatigue crack, which allows us to generate the stress/strain distribution and history near the fatigue crack tip. The continuum deformation history is used as inputs for the micromechanical analysis of lattice strain evolution using the slip-based crystal plasticity model, thus making a mechanistic connection between macro- and micro-strains. Predictions from perfect grain-boundary simulations exhibit the same lattice strain distributions as in neutron diffraction measurements, except for discrepancies near the crack tip within about one-tenth of the plastic zone size. By considering the intergranular damage, which leads to vanishing intergranular strains as damage proceeds, we find a significantly improved agreement between predicted and measured lattice strains inside the fatigue process zone. Consequently, the intergranular damage near fatigue crack tip is concluded to be responsible for fatigue crack growth.     

干态下车轮材料表面疲劳裂纹萌生试验研究

利用WR-1轮轨滚动磨损试验机,结合安定极限理论研究了干态下影响车轮材料表面疲劳裂纹萌生与扩展的因素,探究了表面疲劳损伤形成机理和演变规律.结果表明:随垂向力、横向力和冲角增大,表面疲劳裂纹越容易萌生扩展;冲角对表面疲劳裂纹的萌生与扩展起着重要作用,大冲角下斜线状表面疲劳裂纹萌生扩展明显;只有横向力而不存在冲角时,试样表面不会出现斜线状表面疲劳损伤;车轮试样在周期性循环载荷作用下在表面先形成塑性流动,然后沿轮轨表面切向力方向扩展成斜线状的表面疲劳起皮剥落损伤;垂向力是影响表面裂纹萌生时间的重要因素之一.     

A Piezoelectric Technique for Evaluation of Crack Closure

The ability of the piezoelectric materials to work as sensors and actuators was employed in a technique for monitoring the degree of crack closure and to detect the crack opening load. The technique is demonstrated through experiments with a cracked beam. It consists in exciting the specimen with a piezoelectric actuator and recording the electromechanical response of piezoelectric sensors placed near the crack mouth, while applying a bending moment to open the crack. The sensors in the neighborhood of the crack present a reduction in the amplitude response signal due to the progressive decrease of the dynamic strains near the crack, as the bending load causes the crack to open, reducing the contact between the surfaces of the fatigue crack and the load transmission through the contact area. The results show that the method has a high sensitivity to the state of crack closure, allowing for the direct determination of the crack opening load.     

压电切口张开角和深度对其尖端力电损伤场的影响

基于三维各向异性压电损伤本构理论,导出了广义平面应力问题的损伤本构方程,并据此分析了压电薄板板边V形切口尖端附近的力电损伤,研究了切口张开角和深度对切口尖端力电损伤的影响规律．结果发现：和张开角对切口尖端损伤的影响相比,深度的影响更为明显;在张开角对切口尖端力损伤的影响规律方面,压电材料与一般弹塑性材料存在明显差异,原因在于压电切口尖端力电载荷比会随着深度的改变发生很大变化;不同深度下张开角与切口尖端力、电损伤关系曲线随着张开角的增大由发散逐渐会聚,不同张开角下深度与切口尖端力、电损伤关系曲线随着切口加深由会聚逐渐发散,并且电损伤曲线表现得更为明显．     

Seismic behavior of insulated hollow-brick cavity walls using quasi-static experimentation

This paper focuses on an experimental investigation of different types of insulated hollow-brick cavity walls, i.e., walls with a door opening, with a window opening and without any opening, characterized with different tie bar arrangements, subjected to slowly applied cyclic loads. The cracking and damage patterns, strength and stiffness degradation and deterioration, energy dissipation capacity and hysteretic feature are analyzed. Based on the experimental results, the formulae of calculation for the cracking load and the ultimate load of cavity wall are mathematically established. The evaluation equation of strength and stiffness degradation of walls is presented and its parameters are numerically given from regression results. The original characteristic curves of recovery force-displacement of actual specimens under cyclic loads are discussed, and then a standard recovery force-displacement model is suggested with convenient forms for implementation.     

Operator-split damage-plasticity applied to groove forming in food can lids

This paper presents a numerical–experimental analysis of damage engineering applied to a well-known industrial problem. Many food cans are manually opened by raising a tab on the lid, thus initiating a crack, which is propagated along a circumferential groove. The influence of the groove geometry and depth on the opening force and the resistance against premature opening is investigated for some packaging materials, by making use of dedicated experimental techniques and an operator-split damage-plasticity framework. Attention is focused on a small part of the groove at a location halfway the circular crack-path, 90⁰ from the crack initiation point. First, the groove manufacturing is analyzed by pressing a punch into a thin sheet of the material. Grooved specimens are loaded in tension, simulating the internal pressure during sterilization, and in shear, simulating the opening. Experiments have been carried out using a miniaturized tensile/compression stage located in the objective field of an optical microscope. For the computational analysis, an operator-split damage-plasticity model is proposed, where ductile damage is easily operated in conjunction with standard plasticity models. Simulations are done within a geometrically non-linear context, using a hypo-elasto-plastic material model with non-linear hardening and a contact algorithm to simulate the contact bodies in the groove forming process. An arbitrary–Lagrange–Euler (ALE) technique and adaptive remeshing are used to assure mesh quality during the large deformation process. The operator-split procedure used for the solution of the governing equations, allows to make easy use of a non-local damage operator as an extra feature within a commercial FEM package. Experimental results reveal that a reduction up to 20% for the opening force with unchanged pre-opening resistance can be reached with the use of an asymmetric punch for the groove forming. Numerical and experimental results are in good agreement. Simulations show that the industrial process of can lid production can be optimized considerably by controlling damage evolution in the first stage of the process.     

基于裂纹诱导弦挠度的梁开闭裂纹损伤识别

考虑裂纹缝隙效应,建立了Euler-Bernoulli梁中开闭裂纹位置、深度和初始张开角等损伤参数的识别方法．首先,基于梁中开闭裂纹的等效单向扭转弹簧模型,给出了开闭裂纹Euler-Bernoulli梁静力弯曲挠度的显式闭合解．在此基础上,证明了裂纹诱导弦挠度函数由分段三次多项式组成,并基于其构造特征,建立了基于测量挠度的梁中开闭裂纹位置、裂纹等效扭转弹簧柔度、裂纹初始张开角和裂纹上下侧属性等参数的数值识别方法．最后,通过数值实验考察了挠度测量误差和裂纹位置等对裂纹识别结果的影响,结果表明：裂纹位置、裂纹等效扭转弹簧柔度和裂纹初始张开角等的识别误差随挠度测量误差增大而增大,但裂纹识别结果具有较强的鲁棒性,在工程实际中具有一定的应用前景．