Detection of vibration induced fatigue crack propagation using a hybrid method

Abstract

This paper demonstrates a simple technique to detect vibration-induced fatigue cracks using a hybrid method by vibration and acoustic emission techniques. A thin aluminum plate of 6082-T6 was excited using a vibration shaker to achieve a bending mode where the maximum stress exhibited at the plate mid-span. To simulate crack formation, a sharp notch was created. This systematic setup allows mode I crack propagation through plate thickness. The development of cracks over time changed the natural frequency of the plate which leads to the reduction of vibration amplitudes. This experimental technique facilitates the identification of acoustic emission waves during the onset of damage in the presence of noise due to dynamic motion. The effect of crack development on Lamb waves was investigated. The acoustic emission signals were cross-correlated with a Gaussian window of a central frequency of 250kHz. The results show a reduction in the fundamental wave A0, whilst an increase in S0 wave amplitudes at some stages during crack extension. The current experimental work can be an alternative technique for vibration-induced fatigue test evaluation.