Automatic Measurement of Fatigue Crack Length by a D.C. Electrical Potential Difference Method

Abstract

Mainly because of the complicate loading pattern, the recent estimation of fatigue crack growth in ship structures is still insufficient. So, the accurate and efficient measurement of crack length under the complicate loading pattern are needed. In the present study, a measurement system for fatigue crack length in a dynamic state, applied a D.C. electrical potential difference method (EPD method) was developed. Using this system, some crack length measuring were carried out under a dynamic loading condition. Usually, the measurment of crack length using EPD method are held under a static state or a quasi-static state, avoiding effects of the crack tip openning and closing, the plastic zone generation at the crack tip etc.. However, it was found that the crack length measurement in a dynamic state is possible with sufficient accuracy even under a condition in which the delayed retardation effects appear.