An experimental and finite element investigation of fracture in aluminium thin plates

Abstract

Detailed strain and crack-opening measurements have been made on centre crack and double edge crack specimens of aluminium alloys L70 and L71 in plates 1.6 mm thick, using the Moire technique to measure strains in front of the instantaneous crack tip during stable crack growth. The specimen load-displacement curves were also monitored during stable crack growth, using a displacement-controlled loading machine, and fracture resistance (R-) curves calculated. A two-dimensional elastic-plastic finite element program was used in a numerical model of the experiments, with stable crack growth being simulated by relaxation of the nodal reactions ahead of the initial crack tip. The numerical models were used to calculate the energy changes occurring during crack growth and also the Rice J-integral. These parameters were then examined as possible fracture criteria, and a simple energy balance proved adequate in explaining the main features of stable and unstable crack growth. This result was confirmed by modelling fracture data on L70 obtained by other investigators.