Research on Evaluation of Stress-Intensity Factor by Means of A-C Potential Drop Technique

研究了一种基于a-c电位降技术的应力强度因子评价新方法。主要研究结果总结如下：对于二维静止表面裂纹，载荷变化引起的a-c电位差的增加与应力强度因子K_I的增加成正比关系。数量ROO<mu/sigma>被发现是一个有用的参数，以解释加载效应，其中sigma和mu分别是电导率和渗透率。数量ROO<mu/sigma>用gamma.3表示。线阻抗作为薄层沿半椭圆表面裂纹前缘引入。线路阻抗的性质由电流的频率和伽马的变化决定，并通过二维实验将其表示为K_I的函数。提出了一种利用线阻抗模型和电位降变化测量方法来评估三维表面裂纹K_I未知值的方法。通过算例验证了该方法的有效性，其中K_I的估计值与目前报道的弹性分析解吻合较好。考察了电流输入输出探头与电位测量探头之间的几何关系对测量负载变化引起的电位降变化的影响。1992年，研究人员和同事们获得了美国实验力学学会颁发的R.E.彼得森奖，以表彰他们有关目前研究计划的论文。同样在1993年，调查人员和一名同事获得了日本机械工程师学会颁发的JSME奖章。

The research has been performed to develop a new method based on a-c potential drop technique for evaluating stress-intensity factor. The main results are summarized as follows:1. An increment of a-c potential difference caused by a load change was found to have a proportional relationship with an increment of the stress-intensity factor, K_I, for 2-D stationary surface crack.2. The quantity ROO<mu/sigma> was found to be a useful parameter in order to explain the loading effect, where sigma and mu are the conductivity and the permeability, respectively. The quantity ROO<mu/sigma> was denoted by gamma.3. Line impedance was introduced as a thin layer along the front of the semielliptical surface crack. The property of line impedance was determined by a frequency of the current and the change in gamma, which was expressed as a function of K_I by a 2-D experiment.4. A method for evaluating the unknown value of K_I for a 3-D surface crack was proposed by utilizing the line impedance model and the measurements of the change in potential drop.5. The availability of the present method was verified by an example, where the evaluated value of K_I was confirmed to agree well with the solutions of elastic analyses reported so far.6. The effect of geometrical relationship between current input and output probes and potential measuring probes on the measurement of the change in potential drop due to the change in load was examined.In 1992, the investigators and co-workers received the R.E. Peterson Award from the Society for Experimental Mechanics (U.S.A.) for the paper concerned with the present research program. Also in 1993, the investigators and a co-worker received the JSME Medal from the Japan Society of Mechanical Engineers.