Polymer-matrix composites carbon fibre characterisation and damage inspection using selectively heating thermography (SeHT) through electromagnetic induction

Polymer-matrix composites (PMCs) such as glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) are being increasingly used in fields of aerospace, renewable energy, civil and architecture. Damages such as broken fibre, impact and delamination are inevitable during either fabrication or lifetime of PMC structures or components. This work proposed selectively heating thermography (SeHT) through electromagnetic induction and infrared temperature measurement for CFRP characterisation and damage inspection. Broken carbon fibres can be easily identified through SeHT whilst inside delamination is difficult to be inspected due to negative influence of temperature gradient, lateral blur effect, and periodic structures. In order to solve this problem, cross correlation (CC) matched filtering algorithm was proposed to enhance the inspection results. Six CFRP laminate samples with impact damages from 2 to 12 J were tested to verify the proposed methods. The experimental studies show that SeHT is capable of characterising fibres and inspecting surface broken area, whilst CC phasegram is capable of inspecting inner delamination due to elimination of non-uniform heating effect and lateral blurring effect. The dependence of damage for CFRP sample on impact energy was also investigated. Through SeHT and CC matched filtering, characterisation and inspection for CFRP can be achieved.