Ultrasonic, shearography and thermography testing of heat damaged composite materials

Abstract

Composites are being utilised extensively in many industries today, ranging from aerospace and manufacturing to sports. Like all materials in an aircraft, composites can experience heat damage in-service resulting in delaminations and debonding. Eventually, the material will experience degradation in its strength properties and fatigue failure which can be catastrophic.

This report will study the effect of heat on a typical composite material and its resultant defects. Surface defects can be spotted by the human eye but internal damage can only be confirmed by other Non-Destructive Testing methods. Such methods employed in this report are Ultrasonic C-scan, Laser Shearography, and Active Thermography.

The typical composite material used is a Carbon Fibre Reinforced Polymer (CFRP) laminate plate, a variant of fibre composite most common in aircrafts. The lamina type used here is also different from the studies done by Haridas, Wai Chuen and Kah Kian. The laminate was also fabricated in a professional laboratory using the wet lay-up method coupled with hot press curing. The undamaged specimen was also tested, ensuring all defects measured afterwards are a result of the heat applied.

Heat damage is induced on the specimen with a heat gun used at temperatures ranging from 200°C to 350°C for specified time duration and for 3 cycles. The different methods would be used to determine the severity of heat damage after each heating cycle. Characteristics of defect areas and non-defect areas would be discussed. Results would be presented in this report with images and qualitative and quantitative analysis where applicable.

This study also aims to compare the external damage with the internal damage, and the ease and disadvantages of each procedure.