Model-assisted reliability assessment for adhesive bonding quality evaluation with ultrasonic NDT

This work proposes a cost-effective technique to evaluate the reliability of adhesive bonding quality assessment with ultrasonic NDT. Detectability of debonding defects and weak bonds in aluminum-epoxy single lap joints was estimated by the model-assisted probability of detection curves. For those adhesive joints containing three different bonding qualities –debonding at the interface, weak bond with release agent contamination, and weak bond due to faulty curing– numerical models were built. Ultrasonic wave propagation was simulated by using the semi-analytical finite element method via CIVA and validated with experimental investigations. In order to create a parametric study, uncertain parameters and their distribution were determined based on experiments and expertise. Ultrasonic signal responses in the time and frequency domain were analyzed as opposed to defect characteristic values. According to reliability analysis, it is shown that the detection probability of debonding is mostly based on the gate selection and ultrasonic echo amplitude, while weak bond detection requires a more delicate assessment. Frequency-based calculations can improve the detection reliability of weak bonds due to release agent contamination. Weak bonds caused by faulty curing can be detected via frequency domain maximum amplitude or the attenuation of the signal response.