The fracture resistance of layered DRA materials: Influence of laminae thickness

The effect of changes in laminae thickness on the fracture toughness of layered discontinuously reinforced aluminum (DRA) materials tested in the crack divider orientation was studied. Toughness was measured on monolithic DRA materials and layered DRA materials consisting of two layers of DRA materials and one layer of monolithic aluminum. The fracture toughness of the individual DRA laminae was not significantly affected by changes in thickness over the thickness regime presently used in the layered DRA materials, consisting of alternating layers of DRA and a monolithic aluminum alloy. The initiation toughness of the layered DRA materials was found to be independent of both the DRA layer thickness and the aluminum ligament thickness, but greater than that of a monolithic DRA material. The crack growth resistance of the layered DRA materials was evaluated and was found to increase proportionally with the aluminum ligament thickness. The toughness improvements possible in layered DRA materials are summarized while the effects of changes in laminae thickness on the subsequent toughness are discussed via a consideration of the effects of constrained plasticity on the flow and fracture of the constituents.