Fundamental study on initiation condition of creep crack growth.

Abstract

The initiation condition of creep crack growth was studied by using the crack energy density ε as the creep crack parameter. That is, the creep tests of CT specimens of Al alloy were carried out by varying the level of load and the corresponding values of crack energy densities were evaluated by finite element analyses based on the εj-integral, which is path independent without any restriction on constitutive equations. The characteristics of crack energy densities at the initiation times of creep crack growth were discussed, and the initiation condition, in terms of crack energy density, was considered. The results are as follows : (1) The critical value expressed by total crack energy density ε( = ε0+ +ε(cr) +ε0+ : elasto-plastic contribution at the time of load setting, ε(cr) : additional part caused by creep deformation) depends on the level of ε0+. On the other hand, (2) the critical value expressed by ε(cr) seems to be nearly independent of the level of ε0+. Therefore, (3) ε(cr) may be used as a useful parameter for the evaluation of the initiation condition of creep crack growth.