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

Abstract

In the Part II of this paper, two typical specimens, i.e. compact tension shear (CTS) specimen and single edge notched (SEN) specimen, are selected as the numerical cases to analyse the dominance of C*-integral for mixed I/II creep crack under extensive creep. C*-integrals under different loading angles are presented with the same loading level for CTS specimens and SEN specimens. The equivalent creep zone enlarges with the decrease of the loading angle, which implies that the lower creep mixity occupies the larger equivalent creep zone under the same loading level. A normalized stress function method based on the FE calculation is given to obtain the distribution functions of mixed I/II creep crack tip fields. The comparisons of the FE solutions and HRR field are made for CTS and SEN specimens with various crack depths, and it can be found that the loss dominance of C(t) becomes remarkable under those cases close to mode I loading. The Q-parameter computed with the tangential stress is found to be invalid to be used as the constraint parameter for mixed mode creep crack under the extensive creep regime because of the influence of blunting effect. The stress triaxiality along maximum tangential stress (MTS) direction is suitable to be selected as the constraint parameter for the mixed I/II creep crack tip field. The stress triaxiality is independent on the radial distance even in a wide range away from creep crack tip along the MTS direction.