疲劳的基本方法综述与讨论

N. Dowling, S. Thangjitham
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引用次数: 28

摘要

本文综述了基于应力的、基于应变的和基于裂纹扩展的疲劳寿命预测方法,并试图提出一些选择和变化,这些方法可能会提高它们在本科教育中的包容性,并使实践工程师更经常地使用它们。对于基于应力的方法,重点应该转向使用实际部件的数据,并且应该认识到可能会发生低于通常疲劳极限的损伤。同时,修正的Goodman图对平均应力效应的评价应由其他方法代替。通过增加表面光洁度和尺寸的经验调整,可以扩大基于应变的方法在简单情况下的实用性。也可能需要降低应变寿命曲线的长寿命端,以获得与有限组件测试数据的一致性,从而产生特定组件的应变寿命曲线。由于缺乏一套广泛接受的材料常数来描述da/dN与ΔK曲线,因此阻碍了裂纹扩展方法的使用。建议用帕里斯型指数、相关系数和根据Walker方程表征对r比敏感性的第三个常数来表示中间增长率区域,以纠正这种情况。然后应该分别处理低增长率和高增长率区域的极限或渐近行为。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
An overview and discussion of basic methodology for fatigue
This paper broadly reviews the stress-based, strain-based, and crack growth approaches to fatigue life prediction, and it attempts to suggest some choices and variations of these that might enhance their inclusion in undergraduate education and their more routine use by practicing engineers. For the stress-based approach, emphasis should shift toward the use of data on actual components, and it should be recognized that damage below the usual fatigue limit may occur. Also, evaluation of mean stress effects by the modified Goodman diagram should be replaced by other methods. The usefulness of the strain-based approach for simple situations may be extended by adding empirical adjustments for surface finish and size. It may also be desirable to lower the long-life end of the strain-life curve to obtain agreement with limited component test data, producing a component-specific strain-life curve. Use of the crack growth approach is hampered by the lack of a widely accepted set of materials constants for describing da/dN versus ΔK curves. It is recommended that this situation be remedied by representing the intermediate growth rate region with a Paris-type exponent, an associated coefficient, and a third constant that characterizes the sensitivity to R-ratio according to the equation of Walker. Limits or asymptotic behavior for the low and high growth rate regions should then be handled separately.
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