Optimization of electrical-potential methods of measuring crack growth

Abstract

This paper describes an alternating-current electrical-potential system for measuring crack growth that is more sensitive than a corresponding direct-current system and which is capable of a discrimination in crack length of approximately 20 μm. It shows how the positions of the current supply and potential sensing leads can be optimized using two-dimensional finite-element and boundary integral equation methods. Both methods give calibrations which are in good agreement with optical measurements of crack growth and with measurements made using a graphitized electrical analogue paper technique. The boundary integral equation approach is shown to he the more efficient to use for a range of geometries, since it is only necessary to specify the shape of the boundary and redundant information at internal nodes need not be obtained.