On the stress and strain fields ahead of a stationary crack in creeping solids

A set of finite-element calculations has been performed to assess the validity of several commonly used crack tip parameters for creeping solids. Three specimen geometries, single- and double-edge notched, and centre cracked plate have been studied, all using mode I loading under plane-strain conditions. The variation in the steady-state C∗ field with test geometry, the time required to reach steady state, and the stress-strain fields which develop ahead of the crack during the transition to steady state are determined. The results obtained during this transition period are used to derive a new crack tip parameter—a modified amplitude of the HRR field which equals C∗ once a steady state is achieved. A method of estimating this parameter is also developed, which does not require finite-element analysis. The results have significant implications for the interpretation of accelerated laboratory crack growth tests and their application to structural assessment.