Tensile fracture of ultrafine grained aluminum 6061 sheets by asymmetric cryorolling for microforming

The size effect on the mechanism of fracture in ultrafine grained sheets is an unsolved problem in microforming. This paper describes a tensile test carried out to study the fracture behavior and the shear fracture angles of both rolled and aged ultrafine grained aluminum 6061 sheets produced by asymmetric cryorolling. A scanning electron microscope was used to observe the fracture surface. The finite element method was used to simulate the tensile test using the uncoupled Cockcroft-Latham and Tresca criteria and the coupled Gurson-Tvergaard-Needleman damage criterion. It was found that the shear fracture angle decreases gradually from 90 degrees to 64 degrees with an increasing number of passes. The results of simulations using the Gurson-Tvergaard-Needleman criterion show trends similar to the experimental ones. The paper also presents a discussion on the fracture mechanism and the size effect during the tensile test.