对共振频率法检测裂纹扩展量的研究

通过分析电磁共振式疲劳试验机的工作频率与试样柔度之间的关系,推导出相应的计算公式,并设计出利用微型计算机内部时钟信号检测频率的有关电路,测量精度优于0.05Hz.给出的两点标定法,使共振频率法简便易行.用共振频率法和显微镜目测法同时对三种钢材采用紧凑拉伸试样(CT 试样)进行了裂纹扩展速率 da/dN 的测试。两种裂纹检测方法的测试结果吻合很好,从而验证了共振频率法的可靠性和实用性。此种方法在试验数据的采集、处理自动化方面有优势,并且为在特殊环境下(如高温、腐蚀介质等)对裂纹的检测提供了较为简便、有效的手段。

Measurement of Growing Crack Length by Natural Frequency Method

The measurement of the growing crack length is important in fatigue crack growth rate testing.In order to measure the crack growth length automaticaly and without contact,the method of natural frequency has been thoroughly investigated in this paper. The relation of specimen compliance to nature frequency of High Frequency Vibrophore has been analyzed and the corresponding formulas have been derived.According to the requried accuracy of the crack length measurement,a circuit for detecting frequency using the clock signal of a personal computer has been designed.This circuit provids an accuracy which is better than 0.05Hz.The given method of two-point calibration makes the method of natural frequency easier to be used in practice.The fatigue crack growth rates da/dNof compact tension(CT)specimens made of three kinds of steel have been determined by means of both natural frequency and microscope methods.The results obtained from these two methods are in good agreement.This fact shows that the method of natural frequency is reliable and practical.The method can be used in collecting test date automatically and in special enviroments.