The mode I crack growth resistance of metallic foams

A Dugdale-type cohesive zone model is used to predict the mode I crack grow th resistance (R-curve) of metallic foams, with the fracture process charac terised by an idealised traction-separation law that relates the crack surf ace traction to crack opening displacement. A quadratic yield function, inv olving the von Mises effective stress and mean stress, is used to account f or the plastic compressibility of metallic foams. Finite element calculatio ns are performed for the crack growth resistance under small scale yielding and small scale bridging in plane strain, with K-field boundary conditions . The following effects upon the fracture process are quantified: material hardening, bridging strength, T-stress (the non-singular stress acting para llel to the crack plane), and the shape of yield surface. To study the fail ure behaviour and notch sensitivity of metallic foams in the presence of la rge scale yielding, a study is made for panels embedded with either a centr e-crack or an open hole and subjected to tensile stressing. For the centre- cracked panel, a transition crack size is predicted for which the fracture response switches from net section yielding to elastic-brittle fracture. Li kewise, for a panel containing a centre-hole, a transition hole diameter ex ists for which the fracture response switches from net section yielding to a local maximum stress criterion at the edge of the hole. (C) 2001 Elsevier Science Ltd. All rights reserved.