Method For Detecting Damage In CFRP-steel Structures Based On Electromagnetically Excitation Infrared Thermography

Almost all of service steel structures are subjected to damage due to external loads,excessive service,natural disaster,initial design defect etc.Apparently it is necessary to find out the damage and renovate it timely.Carbon fibre-reinforced plastics(CFRPs)are distinguished with their extremely high strength and rigidity and,compared with metals,present better characteristics with a lower weight.In recent years,there has been increasing interest in composite materials,and particularly in CFRPs,in the aerospace and renewable energy industries.Non-destructive testing and evaluation(NDT&E)is important to the safety and reliability in steel structures and equipment.Eddy current pulsed thermography(ECPT)is well established for non-destructive testing of electrical conductive materials,featuring the advantages of contactless,intuitive detecting and efficient heating.The concept of divergence characterization of the damage rate of carbon fibre-reinforced plastic(CFRP)-steel structures can be extended to ECPT thermal pattern characterization.It was found in this study that the use of ECPT technology on CFRP-steel structures generated a sizeable amount of valuable information for comprehensive material diagnostics.The model of the CFRP-glue-steel structures with damage was established using COMSOL Multiphysics? software,and quantitative non-destructive damage evaluation from the ECPT image areas was derived.The results of this proposed method illustrate that damaged areas are highly affected by available information about fibre texture.This proposed work can be applied for detection of impact induced damage and quantitative evaluation of CFRP structures.The main contents of the paper are as follows:(1)The relationship between divergence and transient thermal patterns can be identified and analysed by deploying mathematical models to analyse the information about fibre texture-like orientations,gaps and undulations in these multi-layered materials.The developed algorithm enabled the removal of information about fibre texture and the extraction of damage features.The model of the CFRP-glue-steel structures with damage was established using COMSOL Multiphysics? software,and quantitative non-destructive damage evaluation from the ECPT image areas was derived.The results of this proposed method illustrate that damaged areas are highly affected by available information about fibre texture.(2)A multi-layer discrete wavelets transform and RGB normalization method are proposed to reduce the effect of information about fibre texture-like orientations and background interference.(3)A novel image fusion method using multi-feature and peak region growing is proposed to calculate damage information.(4)The test platform and design different CFRP-steel structure with various damage are set up.It is verified that the multi-layer discrete wavelets transform and RGB normalization method,and the novel image fusion method using multi-feature and peak region growing are feasible to detect the damage in CFRP-steel structure.The results show that the fibre texture and damage feature can be separated by DWT.Because the eddy current induces pulsed heating that has the physical effects of eddy currents and thermal propagation,it can enable the derivation of additional material properties.This can lead to a comprehensive material characterization,which is important for 3D composites with complex anisotropic and inhomogeneous features such as fibre wrinkling and curved-surface structures.