Fracture of a Thin Laminated Foil

The micro-mechanisms of fracture in a laminate composed of an aluminium foil and a polyethene film are considered. The laminate as well as the freestanding layers were fracture mechanically tested. Inspection of the broken cross-sections shows that fracture occurs through necking, i.e., localised plastic deformation leading to a decreasing and eventually vanishing cross-section. This occurs ahead of the crack tip for both freestanding layers and the laminate. The plastic properties and a slip-line theory are successfully used to derive the work of failure. An accurate prediction of the fracture toughness is made for the aluminium foil and the laminate. Even though the toughness of the freestanding polyethene film could not be accurately determined by the theory, its role as a member of the laminate is predicted by the theory with great accuracy. It is shown that the load carrying capacity of the laminate is many times larger than the added load carried by the freestanding layers. The study further indicates that necking may be impeded which may increase the toughness several times. It is also shown how the laminate may be forced to produce multiple necking with a significantly improved toughness as a result.