Mixed mode I/II crack initiation from U-notches in Al 7075-T6 thin plates by large-scale yielding regime

The main goal of the present research is to check to see if the recently proposed Equivalent Material Concept (EMC) can successfully be used together with the well-known brittle fracture criterion, namely the Averaged Strain Energy Density (ASED) criterion, for predicting crack initiation from U-shaped notches in ductile components under mixed mode I/II loading conditions and large-scale yielding regime. For this purpose, first, several tensile tests are carried out on a rectangular thin plate made of Al 7075-T6 and weakened by a centrally located inclined bean-shaped slit with two U-shaped ends of various tip radii, and the load-carrying capacity of the plate is experimentally measured. The experimental observations indicate that the maximum load that each plate could sustain is obtained at the onset of crack initiation from the notch border, which takes place by large amount of plasticity around the notch. Then, in order to avoid using elastic-plastic models for failure predictions, which are complex and time-consuming, the EMC is utilized to equate the considered Al 7075-T6 with a virtual brittle material, for which different fracture models in the context of the linear-elastic notch fracture mechanics (LENFM), like the Averaged Strain Energy Density (ASED) criterion, could be used. It is shown that the combined EMC-ASED criterion could successfully predict the failure loads of the tested U-notched Al 7075-T6 plates for various notch radii and different mode mixities.