Experimental and numerical analysis of in- and out- of plane constraint effects on fracture parameters: Aluminium alloy 2024

Abstract

The influence of in- and out- of plane constraints on the behaviour of a crack under mode I loading conditions is studied. The independence of the stress intensity tensor, with respect to the specimen thickness B shows that under loss of constraint conditions higher order members of the Williams’ tensor expansion must be considered if the experimental results for increasing apparent fracture toughness resulting from decreasing specimen thickness are to be explained. This is achieved using the constraint curves that define the intensity field tensor along the crack propagation direction and can be alternative to the T-stress approach. This approach is then applied to crack instability assessment for program compact tension (CT — positive values of T-stress) and three point bending (3PB— from negative to positive values of T-stress) specimens with different thicknesses. The theoretical results are compared with experimental ones obtained from the research program on aluminium alloy 2024.