A stress criterion for crack growth

A stress criterion for crack growth was developed from test results with 7075-T6 aluminum-sheet specimens containing transverse machined cracks. Stress distributions near the crack tip were obtained using strain gages and by reducing the strain data to stresses with the aid of Reuss plasticity theory. These distributions indicated the biaxial nature of stress at the crack tip, the high stress gradients a short distance from the tip, and the variation in stress-concentration factor with crack length. Crack growth was found to occur when the effective stress at the crack root reached the engineering ultimate strength.