Suitability of constraint and closure models for predicting crack growth in generic configurations

The effective stress intensity factor range ΔKeff is commonly considered to govern the fatigue crack growth and may be estimated through the crack opening stress Sop and the constraint factor α. In the literature closed-form expressions have been developed for estimating both variables in a center-cracked plate with elastic-perfectly plastic behavior subjected to remote uniform stresses. However, such expressions are frequently adopted regardless of geometry, material and loading and, moreover, α is often given a fixed value. The final objective is to assess the suitability of existing constraint and closure models for performing accurate crack-growth predictions in configurations that do not meet the original hypotheses. The region-II growth of a hole-edge crack is predicted in the 42CrMo4 steel by integrating crack growth laws calibrated with data from standard compact tension (CT) specimens. The results show overall better predictions by using the same constraint model for estimating α in both geometries, rather than by treating it as a fitting parameter in CT specimens. Unexpectedly, the predictions obtained at different stress ratios were, in general, more accurate by integrating a non-closure law based on ΔK and independent of Sop and α.

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