Notes on further experiments on crack propagation in tensioned plates subjected to high intensity noise

Abstract

Sonically induced vibrations of structures, especially at high noise intensity levels, can initiate cracks in skins and ribs, or can propagate existing cracks which were caused by mechanical damage or other structural loads. Tests on simple stressed plates, with existing cracks, indicated that the propagation depends on noise intensity and spectrum, stress in the panel, geometrical parameters of the plate and the crack length. Assuming all parameters constant except for the intensity, the indications are that the rate of crack propagation is proportional to square of pressure (straight line relationship when crack propagation rate is plotted on a log scale against intensity in decibels) and the rate of crack propagation is approximately doubled for each 3 dB increase in noise intensity—the ratio varies from just below 2 for pre-buckling short cracks to almost 4 for postbuckling crack lengths, near the failing point. Tests also indicated that for very short crack lengths there was no propagation at all, even at high noise intensities. Increasing the thickness of the plate while keeping other parameters constant resulted in a slower rate of crack propagation below buckling crack length and then much faster crack propagation rates above this crack length.