Theory of Fatigue for Brittle Flaws Originating from Residual Stress Concentrations
Theory of Fatigue for Brittle Flaws Originating from Residual Stress Concentrations
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残余应力集中脆性缺陷的疲劳理论
DOI：
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发表时间：
1983
期刊：
影响因子：
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通讯作者：
R. Cook
中科院分区：
文献类型：
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作者：
E. Fuller;B. Lawn;R. Cook
一个理论制定的一般疲劳响应的脆性缺陷，经历残余应力集中。本文以压痕裂纹为模型裂纹系统，建立了断裂力学基本方程，但其基本结果在陶瓷材料强度表征中具有更广泛的适用性。首先，通过将点接触或线接触缺陷的适当应力强度因子与幂律裂纹速度函数相结合，建立起疲劳微分方程。然后得到静态疲劳情况下的解析解。由此产生的寿命和破坏应力之间的关系示出具有完全相同的幂律形式的常规解决方案的格里菲斯（残余应力自由）缺陷。这种“等效性”被用作将结果扩展到动态疲劳的基础。这些解析解与数值对应的比较定义的理论程序的准确性的限制。然而，虽然形式的寿命关系保持不变，指数和系数的值显着不同的缺陷和无残余应力。因此，应用传统的疲劳理论来评估裂纹速度参数，而不适当地考虑临界缺陷的性质，会导致严重的错误。给出了将压痕缺陷的“视”速度参数直接转换为“真”速度参数的显式转换公式。这些结果的影响有关使用的压痕方法进行材料评价进行了讨论。
A theory is formulated for the general fatigue response of brittle flaws which experience residual stress concentrations. The indentation crack is taken as a model flaw system for the purpose of setting up the basic fracture mechanics equations, but the essential results are expected to have a wider range of applicability in the strength characterization of ceramics. A starting fatigue differential equation is first set up by combining an appropriate stress intensity factor for point- or line-contact flaws with a power-law crack velocity function. Analytical solutions are then obtained for the case of static fatigue. The resulting relation between lifetime and failure stress is shown to have exactly the same power-law form as the conventional solution for Griffith (residual-stress-free) flaws. This “equivalence” is used as a basis for extending the results to dynamic fatigue. A comparison of these analytical solutions with numerical counterparts defines the limits of accuracy of the theoretical procedure. However, while the form of the lifetime relation remains invariant, the values of the exponent and coefficient differ significantly for flaws with and without residual stress. Accordingly, the application of conventional fatigue theory to evaluate crack velocity parameters, without due regard for the nature of the critical flaw, can lead to serious errors. Explicit conversion formulas are given for transforming “apparent” velocity parameters for indentation flaws directly into “true” parameters. The implications of these results concerning the use of the indentation method for materials evaluation are discussed.