THE EFFECT OF DISCONTINUOUS CRACK IN CREEP CRACK GROWTH TESTS

摘要

Discontinuous cracks ahead of the leading crack tip may be present in observedcertain creep crack growth tests as well as in components. In this work, a single crack of different dimensions and distance from the leading crack has been numerically modeled in a compact tension specimen using elastic, elastic-plastic and elastic-plastic-creep loading. In order to examine their effects on fracture mechanics parameters a sensitivity analysis was performed to determine the effects of size and distance of the secondary crack with respect to the main crack, t The elastic analysis shows that the compliance is insensitive small cracks ahead of the main crack. Limit load analyses, assuming an elastic-perfectly plastic material, show that the limit load decreases due to the presence of discontinuous cracks ahead of the main crack. Theload versus plastic load-line displacement response of the specimen was significantly influenced by discontinuous cracking. The J contour parameter and C~*-integral have been evaluated at the three crack tips and the average of all of them derived for the appropriate contours were compared with the valuesobtained from on ASTM E1820 and E1457. Whilst the average values of the contour integral are similar to the ASTM J and C~* values there is significant differences in J and C~* for the individual crack tip values. This need to be further evaluated in future work.