Adhesive Porosity Analysis of Composite Adhesive Joints using Ultrasonic Guided Waves.

Adhesively bonded composite joints can develop voids and porosity during fabrication, leading to stress concentration and a reduced load-carrying capacity. Hence, adhesive porosity analysis during the fabrication is crucial to ensure the required quality and reliability. Ultrasonic guided wave-based techniques without advanced signal processing often provide low-resolution imaging and can be ineffective for detecting small-size defects. This paper proposes a damage imaging process for adhesive porosity analysis of bonded composite plates using ultrasonic guided waves measured by scanning laser Doppler vibrometer. To implement this approach, a piezoelectric transducer is mounted on the composite joint specimen to generate ultrasonic guided waves, which are measured over a densely sampled area. The signals obtained from the scan are processed using the proposed signal processing in different domains. Through the utilization of filter banks in frequency and wavenumber domains, along with the root-mean-square calculation of filtered signals, damage images of the adhesive region are obtained. It has been observed that different filters provide information related to different void sizes. Combining all the images reconstructed by filters, a final image is obtained which contains damages of various sizes. The images obtained by the proposed method are verified by radiography results and the porosity analysis is presented. The results indicate that the proposed methodology can detect the pores with the smallest detectable pore area of 2.41 mm², corresponding to a radius of 0.88 mm, with an overall tendency to overestimate the pore size by an average of 11 percent.