An algorithm for evaluating crack closure from local compliance measurements

A numerical procedure for evaluating fatigue crack closure from load-local deformation data is presented. The local compliance is assumed to vary during the entire loading cycle, including the portion when the crack is fully open. The closure mechanism-related characteristic load levels are identified based on comparisons between the open crack compliance variations upon loading and unloading. This type of compliance analysis is conditioned by an appropriate smoothness of the measured data. Hence, the choice and optimization of the procedure for smoothing of the measured data. Hence, the choice and optimization of the procedure for smoothing the recorded signals is thoroughly addressed in this paper. The performance of the algorithm is evaluated from comparisons between the computed closure parameters and their reference values which have been previously shown to correlate the observed crack growth rate behaviour.