Fatigue Crack Closure in Residual Stress Bearing Materials

M. R. Hill, Jihwi Kim, S. Daniewicz, S. Dean
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引用次数: 10

Abstract

During fatigue crack growth, the two opposing faces of a fatigue crack can make physical contact while unloading from a maximum level of cyclic load, so that the crack tip state at the minimum cyclic load depends on the host geometry, material properties, and loading history. Although significant work has been performed in order to examine the effects of crack face contact, often called crack closure, under variations of applied loading history, little work has been done to understand the details of crack closure in materials that contain bulk residual stress fields. For an elastic material, variations of applied load history create changes in the crack tip behavior that are directly related to the current levels of cyclic stress, with no effect of prior loading. For an elastic-plastic material, variations of the applied load history cause the crack tip behavior to depend on the current and former loading cycles, because of plastic deformation in the crack wake. In an elastic material with bulk residual stress, crack closure occurs because the strain fields locked into the material, which are the source of the residual stress, alter the shape of the crack faces, so that the details of closure depend on the residual stress field and crack geometry. Residual stresses might therefore affect fatigue crack growth in two distinct ways: first, by combining with applied loads to affect the stress intensity factor (at the current crack size), and second, by altering crack closure. We emphasize that the effect of bulk residual stresses on crack closure described here is an elastic effect, which distinguishes it from the more commonly discussed forms of closure, such as arise from plasticity or roughness. The paper describes a means to forecast crack closure due to bulk residual stress fields and assesses schemes to account for its effects on fatigue crack growth.
残余应力承载材料的疲劳裂纹闭合
在疲劳裂纹扩展过程中,疲劳裂纹的两个相对面可以在最大循环载荷卸载时发生物理接触,因此在最小循环载荷下裂纹尖端的状态取决于宿主的几何形状、材料特性和加载历史。尽管为了检验裂纹面接触(通常称为裂纹闭合)在不同加载历史下的影响已经进行了大量的工作,但对于包含大块残余应力场的材料的裂纹闭合细节的了解却很少。对于弹性材料,施加载荷历史的变化会产生裂纹尖端行为的变化,这与当前的循环应力水平直接相关,而不受先前载荷的影响。对于弹塑性材料,由于裂纹尾迹中的塑性变形,施加载荷历史的变化导致裂纹尖端的行为取决于当前和以前的加载循环。在具有大量残余应力的弹性材料中,由于锁定在材料中的应变场(残余应力的来源)改变了裂纹面形状,因此裂纹闭合的细节取决于残余应力场和裂纹几何形状,从而导致裂纹闭合。因此,残余应力可能以两种不同的方式影响疲劳裂纹的扩展:第一,通过与施加的载荷结合来影响应力强度因子(在当前裂纹尺寸下),第二,通过改变裂纹闭合。我们强调,这里描述的体积残余应力对裂纹闭合的影响是一种弹性效应,这与更常见的讨论形式的闭合(如由塑性或粗糙度引起的闭合)区别开来。本文介绍了一种预测由于大块残余应力场而导致裂纹闭合的方法,并评估了考虑其对疲劳裂纹扩展影响的方案。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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