Predicting Crack Location In Plate Using Nonlinear Vibro-Acoustics Method

Tan, Kok Sian (2018) Predicting Crack Location In Plate Using Nonlinear Vibro-Acoustics Method. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

The presence of damage such as a crack in a structure can be due to many reasons. The breakdown due to the presence of crack can arise in three (3) stages, namely the crack initiation, crack propagation and catastrophic overall failure. Therefore, a minor crack occurs in a very sensitive structure such as the aircraft which fails to be indicated or detected at the earlier stage can lead to a major failure in which can cause accident to happen. Hence, it is important to investigate the effect of natural frequency excitation in predicting the crack location in an aluminum plate using the nonlinear vibro-acoustics method as a model to the real scenario. The aluminum plate (AL-2024) with the size of (400mm x 150mm x 2mm) was used as the test specimen. The vibro-acoustics method is a method based on the fact that a high frequency ultrasonic wave propagates in the testing structure is modulated by the low frequency excitation. Besides that, the interaction between a high frequency vibration and a low frequency vibration results in nonlinear acoustic wave modulation. The nonlinear acoustic wave effects are closely related to the energy dissipation in materials or the nonlinear elasticity properties of the materials. Modal test analysis needs to be conducted to find the natural frequencies of the aluminum plate; the screening test and the Finite Element Analysis were applied to ensure the natural frequency obtained was correct. The low and high frequency waves were subjected simultaneously on the aluminum plate by using the mechanical shaker and PZT transducer respectively. The amplitude modulation intensity, R-values were used to determine the effectiveness of the frequency to predict the crack location in the aluminum plate. The knowledge of vibration mode shape needs to be used in order to predict the exact location of the crack in aluminum plate.

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