C(t) dominance of the mixed I/II creep crack: Part I. Transient creep

The mixed type crack is common to be found in engineering practices, however, the characteristics of mixed I/II creep crack tip fields have not been studied thoroughly. The aim of this part of the paper is to study the dominance of C(t)-integral for mixed I/II type creep crack tip field under transient creep. The boundary layer model is presented to investigate the dominance of C(t) under various mixed mode cases. For transient mixed mode creep crack under boundary layer model, C(t)-integral is related with the effective stress intensity factor (SIF). The near field of mixed creep crack tip field can be influenced by the remote T-stress greatly. The maximum tangential stress direction also can be influenced if the remote T-stress level is large enough. The loss dominance of the C(t) presents more remarkable under negative stress under transient creep. The relations of creep mixity factor with remote elastic mixity factor of the boundary layer model is also presented. The T-stress effects on the constraint parameter Q' and Q* are presented. The case that near the pure mode I case presents the most significant loss of constraint compared with the other mixed mode cases. The comparison between the sharp crack and blunted crack is made, and the sharpening effect is found be existed in the pure mode II case which reveals that the situation of mode II case may have a more severe damage process than that of mode I case.