ELASTIC-PLASTIC FRACTURE-MECHANICS ASSESSMENT OF LOW CONSTRAINT ALUMINUM TEST SPECIMENS

Recent studies have shown that the near crack-tip stress field at a gi ven J value is dependent on geometry. This dependence has been linked to the degree of constraint in the geometry, with low constraint geome tries losing J dominance at very low deformation levels. New approache s centred on the use of a two-parameter description (e.g. J-T and J-Q) of the crack-tip stress-strain state have emerged. However, there is a serious lack of experimental and numerical results for low constrain t geometries to quantify the T-stress and Q-value in the literature. T his paper describes details of an experimental and numerical program c arried out on low and high constraint geometries (CCT and TPB) fabrica ted from an aluminium alloy. The results show that the experimental an d numerical fracture toughness values (J,) agree within +/-10 percent. The T-stress and Q-value two-parameter methodologies are successful a t indexing the fracture toughness, ordering the data into a systematic trend of decreasing fracture toughness with increasing T or Q, albeit with some scatter. This allows the use of practical two-parameter fai lure criteria, in the form of J-T and J-Q loci, to predict the behavio ur of cracked components, without the conservatism associated with the use of high constraint test geometries.