The carbon fiber reinforced polymer (CFRP) is widely used in aircraft and wind turbine blades because of their high strength and low weight. The CFRP is sensitive to impact damage and detecting damages in CFRP is important for ensuring the structural safety. This study is conducted to detect impact damages using eddy current pulsed thermography (ECPT). The impact damages were artificially produced by impact energies of 4J, 6J, 8J and 10J, respectively. The structural impact damages lead to non-uniform distribution of eddy current in CFRP excited by coil with high frequency alternating current. The eddy current can be represented by heat distribution according to Joule’s law. And the damages also influence the transmission of heat in the CFRP. The change of heat is represented by surface temperature recorded in the form of thermal image sequence by IR camera. Then defects are evaluated by analyzing the heat distribution and patterns in thermal images. In addition, due to the 4J energy is low, the damage size of the CFRP is small and cannot be observed directly from the original thermal images. In order to distinguish the small defects, a multi-resolution statistical analysis method, employing the wavelet transform combined with principal component analysis (PCA), is used to extract the defective characteristics of impact damage. Through this method, the information of thermal images has been improved to distinguish defects and the detectability of impact energy producing damage are also discussed

This paper reviews recent developments of eddy current pulsed thermography (ECPT) for material characterization and nondestructive evaluation (NDE). Due to the fact that line-coil-based ECPT, with the limitation of non-uniform heating and a restricted view, is not suitable for complex geometry structures evaluation, Helmholtz coils and ferrite-yoke-based excitation configurations of ECPT are proposed and compared. Simulations and experiments of new ECPT configurations considering the multi-physical-phenomenon of hysteresis losses, stray losses, and eddy current heating in conjunction with uniform induction magnetic field have been conducted and implemented for ferromagnetic and non-ferromagnetic materials. These configurations of ECPT for metallic material and defect characterization are discussed and compared with conventional line-coil configuration. The results indicate that the proposed ECPT excitation configurations can be applied for different shapes of samples such as turbine blade edges and rail tracks.

Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF).

The paper reports the design and implementation of magnetic Barkhausen noise (MBN) systems as well as its application and experiments for stress measurement on the rail track. Features of MBN signals including root mean square, average amplitude and pulse counts are calculated and analyzed, and a new feature the ratio of peak value and width at half maximum is introduced. All of these features of MBN signal decreases with the increase of compressive stress, but the feature of the ratio of peak value and width at half maximum has the fastest rate of decreasing against compressing stress which means that it has better sensitivity in stress measurement.