Non-destructive testing of delamination defects in GFRP patches using step heating thermography

Composite materials are extensively used for repairs in the different industries, where their quality is monitored by nondestructive testing. Through this work, the functional role of step-heating thermography on the detection of delamination defects in multi-layer GFRP composite patches are investigated. Specimens prepared for testing were GFRP patches of different thicknesses (4 and 8 layer laminates) which were mounted on to the aluminum plates. In order to create interlaminar separation, kepton sheets of miscellaneous sizes were incorporated between the laminas, during the patch manufacturing. The defects were arranged at the edge and center of different layers, simultaneously. After applying of step heating by using of flash lamps to the manufactured samples, the factors affecting the defect identification (thermal intensity and size difference percentage) were investigated. The results showed that all defects in both 4 and 8 layer laminates were identified in the thermal images were the dimensional accuracy of the defect size was 30% higher in 8 layer patch due to the lesser reflection of heat to the IR camera.