Prediction of unstable crack length in aluminium alloys

A method was set down for predicting the unstable length of a crack in a flat sheet of aluminium alloy subjected to a steady tensile stress. The basis of the method was to take the work done to failure in the 'neck' region of a tensile test specimen and apply it, with a suitable constraint factor, to the flat sheet to give the work rate required to propagate the crack. Experimental evidence is produced in support of the method.