Abstract:

An experimental method is developed to predict crack growth, and ultimately failure, in a dynamically fatigued tensioned steel band. The transfer function across the double edge notched crack is measured. The band's modal response changes as the crack progresses, due to a change in the crack's equivalent compliance and a reduction in the remaining area of the material. The frequencies of the transfer function are tracked throughout the fatigue cycle, and the changes in frequencies are used in estimating crack growth and failure. A general trend shows that the resonance frequencies drop as the crack grows. When the material starts to approach failure, the frequencies stop dropping, and in some cases rise. This is an indication that failure can occur at any time. Just before failure, the modal frequencies drop rapidly, until the band breaks. Using the general trends in the change in the bar's frequency response it is possible to predict failure.