Fatigue crack closure of a corner crack: A comparison of experimental results with finite element predictions

Plasticity induced corner crack closure has been examined for the case of a middle tension (MT) plate of 14 mm thick 2024-T351 aluminium alloy subjected to cyclic loading. The closure load has been found by comparing the strain just ahead of the crack tip with the far field strain as the specimen was loaded and then unloaded. Special crack detection strain gauges were placed in front of the crack tips on the bore surface and on the free surface to allow measurement of crack opening and closure stress as the crack propagates. The offset observation and slope variation methods were used to determine the crack opening and closure stress levels. A three-dimensional finite element closure model was developed for a corner crack emanating from a hole. Finite element analysis gives the displacement of each node around the crack for which the opening and closure load were evaluated. The fatigue crack closure stress levels from the finite element analysis were compared with the experimental results giving a good agreement.