Fracture analysis of cracked Macadamia nutshells under contact load between two rigid plates

Fracture behaviour of Macadamia nutshells with an existing crack, compressed between two rigid plates, is investigated theoretically and numerically. In terms of a crack closure theory developed within a linearized shallow shell theory, the stress intensity factors for the cracked nutshells are determined over a range of crack lengths. Two typical crack configurations in a nutshell, defined as the vertical crack and the horizontal crack, respectively, with reference to the loading planes, are studied. The finite element analysis is carried out for comparison with the theoretical solutions, and it is shown that the shallow shell theory is valid only for a shallowness parameter up to 0.25. The linear variation of the stress intensity factor through the shell thickness, which is assumed in the shell theory, is confirmed by the finite element analysis. (C) 1999 Silsoe Research Institute.