EFFICIENT AND ACCURATE DETERMINATION OF MODE-I TYPE 3-D SURFACE CRACKBY MEASURING STRAIN AROUND THE CRACK ON THE IDEA OF THE BODY FORCE METHOD

In this study, the location and the size of a three-dimensional semi-e lliptical surface crack in a semiinfinite body are detected from data of strains measured around a region of the crack. Also the loading str ess at infinity is treated as an unknown parameter. The crack location , size and the loading stress are determined through the condition whi ch minimizes the square sum of residuals between measured strain distr ibutions and computed ones for an assumed crack. The body force method is used to calculate the strain field around the crack. In order to o btain the solution with short CPU time, the crack is represented by a set of force doublets, and the database of the magnitudes of force dou blets for various aspect ratios of the crack is utilized. The method o f gradient search is employed to find out an optimal set of parameters . The fact that the strain field around the surface crack is mainly do minated by the crack area is utilized in detecting the crack. Several inversion schemes are examined to obtain accurate results. Numerical s imulations are carried out and the results show that crack location, s hape and loading stress are determined efficiently with good accuracy.