Thermal pattern contrast diagnostic of microcracks with induction thermography for aircraft braking components

Reciprocating impact load leads to plastic deformation on the surface of the kinematic chains in aircraft brake system. As a result, this causes fatigue and various complex natural damages. Due to the complex surface conditions and the coexistence damages, it is extremely difficult to diagnose micro cracks by using conventional thermography inspection methods. In this paper, the Thermal Pattern Contrast (TPC) method is proposed for weak thermal signal detection using eddy current pulsed thermography (ECPT). In this process, the extraction and subsequent separation differentiate a maximum of the thermal spatial-transient pattern between defect and non-defect areas. Specifically, a successive optical flow (OF) is established to conduct a projection of the thermal diffusion. This directly gains the benefits of capturing the thermal propagation characteristics. It enables us to build the motion context connected between the local and the global thermal spatial pattern. Principal Component Analysis (PCA) is constructed to further mine the spatial-transient patterns to enhance the detectability and sensitivity in micro crack detection. Finally, experimental studies have been conducted on an artificial crack in a steel sample and on natural fatigue cracks in aircraft brake components in order to validate the proposed method.