On assumptions associated with Δ Keff and their implications on FCG predictions

Abstract

In this paper, an assessment of commonly used assumptions associated with Δ K eff and their implications on FCG predictions in light of existing experimental and numerical data is presented. In particular, the following assumptions are examined: (1). Δ K eff fully describes cyclic stresses and strains at the crack-tip vicinity. (2). K op can be determined experimentally or numerically with certain accuracy. (3). Overload alters K op but not K max and associated σ max at the crack-tip ‘process zone’. (4). Contact of crack faces curtails the crack driving force in terms of Δ K eff. The analysis indicates that there is insufficient support to justify the above assumptions. In contrary, the analysis demonstrates that a two-parameter fatigue crack driving force in terms of Δ K and K max, which accounts for both applied and the internal stresses should be used in FCG analyses and predictions.