Volume or inside heating thermography using electromagnetic excitation for advanced composite materials

• Volume heating thermography was proposed for advanced composite materials.
• Physical principle of VHT and IHT for defect quantification was investigated.
• Three VHT methods in style of pulse and step analysis in time domain and phase analysis in frequency domain were built.
• The insert, impact and delamination in CFRP can be detected and characterised.

Conventional active thermography heats the surface of materials by using conductive thermal sources like hot water, convective thermal sources like air jet, or irradiative thermal sources like a flash lamp. Quantification and characterization methods are mainly built on heat conduction from surface to inner. Currently, electromagnetic induction, microwave and terahertz wave are increasingly used for heating advanced materials such as composites, polymers and biomaterials. Their heating principles and quantification methods vary widely from that of conventional surface heating thermography. This work presented volume heating thermography (VHT) and inside heating thermography (IHT) for advanced composite materials through these electromagnetic excitations. Physical principle of VHT/IHT for defect quantification has been investigated, and several specific VHT/IHT methods have been built in style of (square) pulse and step analysis in time domain and phase analysis in frequency domain, such as volume lock-in thermography. 1D solution, simulation involving 3D finite element model and experiments studies demonstrate that polytetrafluoroethylene insert, impact, and delamination in carbon fibre reinforced polymer can be qualitatively detected and characterised using proposed methods, especially in phasegram after eliminating non-uniform heating effect and periodic structures. VHT and IHT through electromagnetic induction, microwave and terahertz wave have a potential application on inspection and characterization of composites, polymers and biomaterials.