Sensitivity analysis of shearography on defect detection in graphite composites

• Main Author: Dhanaraj, Justin Anthony
• Other Authors: Murukeshan Vadakke Matham
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Materials::Composite materials
• Online Access: http://hdl.handle.net/10356/72970
• Institution: Nanyang Technological University

This project aims to investigate the capabilities of shearography against the traditional ultrasound C-scan technique in the defect detection of delaminations in composites. Shearography is an optical non-destructive testing (NDT) method employed to identify sub surface defects in composites. This method uses a coherent laser light source to measure the displacement derivatives of these defects. The specimen must undergo loading with the help of heat, vibration or other physical means to detect these defects. The defect reacts differently than the surrounding material to these loading methods. This difference gives rise to a mechanical change which the shearography system can measure and via subsequent image processing techniques relevant information relating to the defect can be obtained. Ultrasound is a conventional NDT technique that utilises sound waves to identify defects in structures. A frequency probe sends a sound wave through the specimen and gets reflected into the system where it shows up as a reflection peak. When the sound wave gets reflected by a defect, it loses energy and gets detected faster by the system where its resulting peak would be lower. Ultrasound consist of various scan types such as A, B and C. This project would focus on C-scans utilises tomography to help identify the defect area from the cross-section of the respective scan area. Composite materials represent the combination of materials that have enhanced properties than its constituent elements which make it desirable for usage. Defects in these materials can manifest either during the manufacturing process or after periodic usage. These defects significantly affect the reliability of these composite structures and pose a high safety risk regarding its respective application. However, the presence of defects can make it difficult to be detected by conventional non-destructive techniques (NDT) due to non-homogeneity of the combined materials. Adopting new NDT techniques is pertinent to ensure time efficiency and cost savings. This project uses ultrasonic C-scan inspection technique as a conventional NDT technique while adopting shearography as the new NDT technique. Shearography is still a relatively new technique and would require extensive research to better understand its capabilities against other traditional methods such as ultrasound. In this context, this project aims to establish a means of comparison between these two techniques to identify delaminations in graphite fiber reinforced polymer composites (GFRP). The results of this investigation will be crucial in conducting future experiments.