A BOUNDARY-ELEMENT MODEL OF PLASTICITY-INDUCED FATIGUE-CRACK CLOSURE

This paper describes a plane stress boundary element model of plastici ty-induced fatigue crack closure. A simple Dugdale-type strip yield zo ne is used and quadratic programming techniques are employed to establ ish crack shape, stress and plastic deformation. The technique is extr emely effective and the model can be readily implemented on a personal computer. Predictions of crack closure behaviour are produced for cra cks growing under constant amplitude loading, and also following an ov erload or overload/underload cycle. These results are compared with an empirical R-ratio correction due to Walker and with experimental meas urements taken from the literature. The model is found to give good pr edictions of crack behaviour under constant amplitude loading. Predict ions for crack closure levels following an overload cycle give qualita tive agreement with experimental results; the differences observed may well be due to the different definition of crack closure in the exper iments.