Abstract: According to the prediction problem of crack growth of mechanical structures, a crack growth rate model of a V-notched beam by using the decrease ratio of modal frequency was investigated. The experimental system for a V- notched beam was designed, and the modal frequency test and the crack growth test were carried out for 4 specimens. Factors that affect the behavior of the crack growth were discussed by analyzing the experimental results. And the equation of crack growth rate of a V-notched beam was fitted by the Paris model, the relation between the decrease ratio of the modal frequency and the stress intensity factor (SIF) was discussed. Combing the relation of the decrease ratio of the modal frequency， the crack depth and the loading cyclic numbers, the crack growth rate model was proposed by using the decrease ratio of the modal frequency in the end. Results indicate that the crack growth rate of the V-notched beam increases with the increasing of the decrease ratio of the first modal frequency monotonically. And also, the amplitude of the SIF increases with the increasing of the decrease ratio of the first modal frequency monotonically. The predicted crack growth rate is agreement with the experimental results basically. The proposed crack growth rate model will help the monitoring of the crack growth of a beam.

Key words: Crack growth;Rate model;Notched beam;Modal frequency;Stress intensity factor

摘要： 针对机械结构裂纹扩展预测问题，研究了基于模态频率下降率的V型缺口梁裂纹扩展速率模型。设计了V型缺口梁的疲劳裂纹扩展实验系统，完成了4个试件的模态频率和裂纹扩展实验测试。基于实验结果，讨论了影响V型缺口梁裂纹扩展行为的因素，应用Pairs模型拟合了V型缺口梁的裂纹扩展速率方程，探讨了模态频率下降率与应力强度因子的关系。结合模态频率下降率与裂纹扩展长度及循环加载次数的关系，建立了基于模态频率下降率的裂纹扩展速率模型。结果表明，V型缺口梁的裂纹扩展速率随模态频率下降率增加单调递增，裂纹尖端的应力强度因子幅值也随模态频率下降率增加单调递增，基于模型预测的裂纹扩展速率与实验结果基本吻合。所提出的基于模态频率的裂纹扩展速率模型有助于梁的裂纹扩展监测。

关键词: 裂纹扩展;速率模型;缺口梁;模态频率;应力强度因子