Fatigue properties of aluminium foams at high numbers of cycles

Endurance fatigue experiments have been performed with two kinds of Al-Mg-S i foams and one AI-Si foam under fully reversed loading conditions using th e ultrasound fatigue testing method. Young's modulus of the foams is 3.9 GP a. Constant amplitude fatigue data show endurance limits on the basis of 10 (9) cycles between 1.1 and 1.4 MPa which is 16-23% of the plateau stress. L ifetimes exhibit a pronounced scatter, which is caused by the inhomogeneous structure of the foams. Fatigue damage is governed by the formation of cra cks, which preferentially initiate in the interior sections of cell walls a t initial defects, like precracks or holes. No strain localization and form ation of deformation bands was found. Fatigue crack growth preferentially f ollows areas of cell walls with a minimum wall thickness, and eventually ma y stop near cell-nodes. The cyclic properties of foams can be improved, if initial defects are small, if the mean cell sizes are reduced, and if a mor e homogeneous foam is obtained. (C) 2000 Elsevier Science S.A. All rights r eserved.