Shear ligament phenomena in Al–Si alloys

Abstract

Fracture problems in Al–Si alloys involve mixed mode (shear and opening) displacements in the aluminium matrix along the crack surface. Subject to such displacements, fracture must be influenced by the non-planarity of microcracks which depends on many factors including particle and slip orientation. Instead of producing brittle cracks along silicon particles clusters, a number of shear bands are formed in the aluminium matrix ligaments between microcracks. Shear ligaments, which are ligamentlike structures connected between microcracks, were observed on the tensile specimens. They undergo ductile fracture by shearing and enhance fracture toughness. This toughness was estimated by a micromechanical model. The amount of toughening depends on the ligament length, a ligament toughness parameter representing the work to fracture, the area fraction of the ligament, and the area fraction of frictional contact.