Method for predicting crack size using amplitude change in titanium alloy under bending vibration

The natural frequency of a material decreases owing to the presence of cracks. Thus, when a crack initiates in a material under vibration, the amplitude of the vibration changes with the crack propagation. In this study, we investigated a method for predicting crack size using the amplitude change in a plate specimen of a titanium alloy under bending vibration. The bending displacement amplitudes were measured using high-speed camera images of the specimens. The crack sizes were measured using optical microscopy images of plastic replicas of the specimen surfaces that were obtained after interrupting tests at specified intervals. By using the relationship between the total area of the cracks and bending displacement amplitude for tests at two different vibration frequencies as well as the relationship between the vibration frequency and bending displacement amplitude for an undamaged specimen, the bending displacement amplitude at any vibration frequency can be monitored to predict the total area of the cracks.