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

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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.