Coded Thermal Wave Imaging Based Defect Detection in Composites using Neural Networks

Industry 4.0 focuses on the deployment of artificial intelligence in various fields for automation of variety of industrial applications like aerospace, defence, material manufacturing, etc. Application of these principles to active thermography, facilitates automatic defect detection without human intervention and helps in automation in assessing the integrity and product quality. This paper employs artificial neural network (ANN) based classification post-processing modality for exploring subsurface anomalies with improved resolution and enhanced detectability. A modified bi-phase seven-bit barker coded thermal wave imaging is used to simulate the specimens. Experimentation has been carried over carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) specimens using artificially made flat bottom holes of various sizes and depths. A phase based theoretical model also developed for quantitative assessment of depth of the anomaly and experimentally cross verified with a maximum depth error of 3%. Additionally, subsurface anomalies are compared based on probability of detection (POD) and signal to noise ratio (SNR). ANN provides better visualization of defects with 96% probability of detection even for small aspect ratio in contrast to conventional post processing modalities.