Thickness dependence of cracking resistance in thin aluminium p1ates

摘要

The influence of thickness on the fracture toughness of aluminium 6082T0 thin plates of l--6 mm thicknesses was investigated experimentally and numerically from tensile testing of cracked DENT specimens. The critical J-integral, Jc, critical CTOD, δcToDc, and essential work of fracture, We, are found to increase with thickness and to constitute equivalent measures of fracture toughness at small thickness. For larger thickness, Jc and δCTODc. increase non-linearly with thickness and reach a maximum for 5--6 mm thickness whereas We keeps increasing linear1y with thickness. This difference is related to a more progressive development of the necking zone in front of the crack tip when thickness increases: at large thickness, cracking initiates well before the neck has developed to its stationary value during propagation. We is more directly related to the steady-state crack growth resistance. A linear regression on the fracture toughness/thickness curve allows further separation of the two contributions of the essential work of fracture the necking work and the fracture work spent for damaging. The maximum of the stress triaxiality ratio is shown to constitute a pertinent parameter for characterising how constraint affects cracking initiation in the present context where out-of-plane constraint dominates in-plane constraint. It allows justifying the shape of the Jc/thickness relationship and results in the proposal of a 3D Jc/ thickness/triaxiality fracture locus.