Pulsed Air-Flow Thermography for Natural Crack Detection and Evaluation

Thermography is one of advanced non-destructive test and evaluation for imaging defects. This paper proposes pulsed air-flow thermography for sample surface crack detection and evaluation. The proposed approach combines the advantages of both convection heat transfer of air-flow and solid heat conduction. By controlling the pulse width, the heat waves of different frequencies can be modulated to penetrate materials with different thermal conductivity. And the cleaning degree of specimen surface can be improved by high-speed air-flow convection. The theoretical model and experimental facilities of air-flow thermography are presented. Meanwhile, the offline detection of rail surface defects and the dynamic test of the defects on the outer cylindrical surface of the turn-plate are completed. The offline experiments are conducted to identify the characteristics of the proposed method for the detection of artificial and natural cracks. And the dynamic experimental results show that the defects on the outer cylindrical surface of the turn-plate can be identified when the linear velocity at the edge of the turn-plate is 1.356km/h and 6.782km/h. The results demonstrate the proposed method on testing and evaluation for rail surface cracks is effective at the low speed.