Impact-Acoustic Evaluation Method of Internal Crack in Rubber Composite Structure

The main objective of this work is to investigate the impact acoustic method as a means of nondestructive testing (NDT) for internal cracks in a rubber composite structure, such as that found in a tire. As demonstrated in this dissertation, this approach is an effective and economical alternative to the current NDT methods for tires casing integrity inspection. There are two separate aspects of the impact acoustic signals considered in this work: the impact force signal and the resultant acoustic signal. First, a contact dynamics model is developed based on the Hertz’s impact theory and modified for rubber composite materials. The model generates prediction of major impact dynamics quantities, which are theoretically proven to be sensitive to the existence of internal structural cracks. For the purpose of applying the impact acoustic method for tire casing integrity inspection, models are developed for simplified tire structures, which are a cubic shape comprised of rubber compound material without reinforcements. The prepared cubic rubber samples are designed to roughly approximate the profile of the sectional tire casing and the cracks embedded at the belt edge in the shoulder area. The rationality of the simplification is explained both theoretically and experimentally. Based on comprehensive theoretical analysis of the impact acoustic signals, several direct and indirect experimental features are identified that are equivalent to the theoretical dynamic quantities, thus correlated to the presence of internal crack. The experimental discriminators can be extracted from either impact force signal or acoustic time- and frequency-domain signal. They are verified as promising indicators of internal crack in both simplified cubic rubber structures and complicated tire casings. Integration of the experimentally extracted discriminators helps to mitigate the deficiencies and noise caused by relying heavily on a single discriminator, while providing an integrated index identifying the damage conditions with good accuracy and robustness