Pulsed electromagnetic NDE for defect detection and characterisation in composites

Carbon fibre reinforced plastic (CFRP) materials are widely used in aircraft and wind turbine blades due to the low weight and high strength. Surface cracks, impact damage and delaminations are the most common defects for CFRP composites. In this paper, a pulsed eddy current (PEC) stimulated thermography is developed to detect and characterise these three types of defects from the heating patterns. In addition, different heating patterns and transient temperature responses enable defect classification using principal component analysis (PCA). Through feature extract from transient response, the physical properties such as electrical and thermal conductivity can be extracted and presented. In this paper, in addition to different defect characterisation, quantitative non-destructive evaluation for impact damage of composite has been investigated. The relationships between electrical and thermal conductivity distribution and impact energy from 4J to 12J are achieved through numerical modelling and experimental study. It has found that as impact energy increases (not large enough to generate surface crack), electrical conductivity in the impact area decreases, and, thermal conductivity increases.