Closed crack sizing using a standard pulse echo method and a transient thermal solicitation

Closed crack sizing using conventional linear ultrasonic methods is hindered by the transmission of waves through local contacts between crack lips. Nonlinear acoustic methods, while offering potential solutions, often require complex experimental protocols and restrictive conditions. This study presents a novel approach that enhances conventional NDT by applying transient local cooling to closed cracks. The resulting thermal diffusion temporarily opens the closed portions of the crack, enabling accurate depth measurement using a standard pulse echo technique during this transient state. The method's effectiveness is demonstrated on fatigue cracks in both laboratory samples and industrial low-alloy steel parts. The results demonstrate significant improvements in crack detection and sizing, making it a promising, cost-effective solution for various industries, including nuclear energy and naval.