EXPERIMENTAL K-CALIBRATION OF ELLIPTIC SURFACE CRACKS UNDER BENDING

The geometrical correction function in the expression for K has been determined experimentally by a compliance technique for elliptical surface cracks in bar-shaped specimens under pure bending at R = -1. Although the investigation did not allow one to distinguish between K-values at the surface and at the bottom of the crack it was possible to resolve the different behaviour of the crack opening in the tensile and the compressive portions of the loading cycle. The results show good agreement with literature data determined by FE analysis for tensile loading. For loading at negative R-ratios the determined correction function should be used with an additional parameter. It seems feasible to apply this function to different negative R-ratios.