Using finite element to estimate vibration energy loss by cracks in thermosonic phenomenon under chaotic and non-chaotic vibrations

Abstract

Thermosonic tests are capable of detecting surface defects such as fatigue cracks. The mechanism of its operation is based on the stimulation of structural vibration of the test piece which generates detectable displacements between crack surfaces. The main problem with using a thermosonic test is the uncertainty caused by chaotic and non-reproducible vibrations of the test piece. Consequently, the study of effective parameters such as, for example, the frequency and amplitude of vibration, crack size, vibration damping around the crack, and acoustical chaos could play a major role in improving this method to make it a highly reliable non-destructive test. In this study, an algorithm has been used to estimate the wasted vibration energy caused by extra damping due to the presence of cracks in the sample. Initially, the validity of the discussed algorithm is studied and findings compared with the results of other experimental studies available in the literature. Subsequently, a simulation process of the thermosonic test in a beam in two conditions of chaotic and non-chaotic vibrations take place. Then, findings are compared with the desired algorithm. Results indicate that in a non-chaotic vibration condition, the measured wasted energy by the algorithm is confirmed by the results obtained from the finite element. However, in a chaotic vibration condition, when the crack size is large enough, there is considerable difference between the results of the finite element method and the algorithm. This difference is due to the occurrence of acoustic chaos while stimulating the test piece. The used algorithm was unable to predict this.