Defect detection capability of pulsed transient thermography

Abstract

Pulsed thermography is gaining wide acceptance in the aerospace, automotive and power generation industries, owing to its quickness of inspection, repeatability and sensitivity. Recently, advancement in pulsed thermographic data processing has been made by Thermal Wave Imaging Inc (TWI) in USA. A technique called thermographic signal reconstruction (TSR) has been devised. By approximating the raw data sequence with logarithmic polynomial function, this technique produces three types of images, namely: the synthetic image and first and second time derivative images. These images facilitate detection of smaller and/or deeper defects, which are undetectable on the raw data sequence. In this work, qualitative and quantitative assessments of the TSR images have been conducted using aluminium, CFRP and GFRP composites and mild steel samples. Results have validated the significant enhancement of the TSR process. A quantitative study performed using CFRP composite has shown that an improvement of 60% in detection depth has achieved for defects greater than 4 mm diameter. Defects have been imaged at depths greater than 5 mm in composites.