On assumptions associated with ΔKeff and their implications on FCG predictions

In this paper, an assessment of commonly used assumptions associated with ΔKeff and their implications on FCG predictions in light of existing experimental and numerical data is presented. In particular, the following assumptions are examined: (1). ΔKeff fully describes cyclic stresses and strains at the crack-tip vicinity. (2). Kop can be determined experimentally or numerically with certain accuracy. (3). Overload alters Kop but not Kmax and associated σmax at the crack-tip ‘process zone’. (4). Contact of crack faces curtails the crack driving force in terms of ΔKeff. 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 ΔK and Kmax, which accounts for both applied and the internal stresses should be used in FCG analyses and predictions.