Patankar Ravindra
Mechanical Engineering--Engineering Mechanics, Michigan Technological University, Houghton 49931, USA.
Risk Anal. 2003 Oct;23(5):929-36. doi: 10.1111/1539-6924.00370.
Statistical fatigue life of a ductile alloy specimen is traditionally divided into three stages, namely, crack nucleation, small crack growth, and large crack growth. Crack nucleation and small crack growth show a wide variation and hence a big spread on cycles versus crack length graph. Relatively, large crack growth shows a lesser variation. Therefore, different models are fitted to the different stages of the fatigue evolution process, thus treating different stages as different phenomena. With these independent models, it is impossible to predict one phenomenon based on the information available about the other phenomenon. Experimentally, it is easier to carry out crack length measurements of large cracks compared to nucleating cracks and small cracks. Thus, it is easier to collect statistical data for large crack growth compared to the painstaking effort it would take to collect statistical data for crack nucleation and small crack growth. This article presents a fracture mechanics-based stochastic model of fatigue crack growth in ductile alloys that are commonly encountered in mechanical structures and machine components. The model has been validated by Ray (1998) for crack propagation by various statistical fatigue data. Based on the model, this article proposes a technique to predict statistical information of fatigue crack nucleation and small crack growth properties that uses the statistical properties of large crack growth under constant amplitude stress excitation. The statistical properties of large crack growth under constant amplitude stress excitation can be obtained via experiments.
传统上，韧性合金试样的统计疲劳寿命分为三个阶段，即裂纹形核、小裂纹扩展和大裂纹扩展。裂纹形核和小裂纹扩展呈现出很大的变化，因此在循环次数与裂纹长度的关系图上分布很广。相对而言，大裂纹扩展的变化较小。因此，针对疲劳演化过程的不同阶段拟合了不同的模型，从而将不同阶段视为不同的现象。使用这些独立的模型，无法根据关于另一种现象的可用信息来预测一种现象。在实验上，与形核裂纹和小裂纹相比，测量大裂纹的裂纹长度更容易。因此，与收集裂纹形核和小裂纹扩展的统计数据所需的艰苦努力相比，收集大裂纹扩展的统计数据更容易。本文提出了一种基于断裂力学的韧性合金疲劳裂纹扩展随机模型，这种合金常见于机械结构和机器部件中。Ray（1998年）已通过各种统计疲劳数据对该模型的裂纹扩展进行了验证。基于该模型，本文提出了一种技术，用于预测疲劳裂纹形核和小裂纹扩展特性的统计信息，该技术利用恒幅应力激励下大裂纹扩展的统计特性。恒幅应力激励下大裂纹扩展的统计特性可通过实验获得。
