ABSTRACT

Two original methods using lock-in thermography with a laser excitation are proposed for the estimation without contact of open crack depths in metal. The first uses a modulated punctual thermal source and is well suited for the study of complicated structures. In the second, a continuous moving thermal source allows to scan homogeneous structures. Each method relies on the heat diffusion modifications induced by a crack located in the thermal diffusion area of the synchronised heat source. The thermal signature of the crack is extracted to the amplitude of surface temperature images for various modulation frequencies or various scanning speeds of the thermal source. The thermal signatures are analysed according to a length representative of the thermal diffusion length to give a local evaluation of the crack depth. The obtained results demonstrate the potentiality of active lock-in thermography as a contactless measurement tool for the evaluation of crack depths up to 3 mm.

摘要

提出了两种使用锁定热成像和激光激发的原始方法进行估算，而无需接触金属中的开放裂纹深度。第一种使用调制的点温热源，非常适合于复杂结构的研究。第二，连续移动的热源可以扫描均匀的结构。每种方法都依赖于由位于同步热源的热扩散区域中的裂缝引起的热扩散修正。对于热源的各种调制频率或各种扫描速度，将裂纹的热特征提取为表面温度图像的振幅。根据代表热扩散长度的长度来分析热特征，以对裂纹深度进行局部评估。