Abstract
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.
Highlights
The carbon fiber reinforced polymer (CFRP) composite can be defined as a combination of two or more materials with different ways
The Eddy current pulsed thermography (ECPT) and the proposed computation show the detectability of low energy impact damages up to 4 J impact visible damage after thermal images processing with proposed method combining wavelet transform and PCA
Even the surface of CFRP specimen has no plastic damage in low impact energy, the interior may have defects such as crack and fiber fracture which lead to mechanical properties such as compressive strength fallen dramatically
Summary
The carbon fiber reinforced polymer (CFRP) composite can be defined as a combination of two or more materials with different ways. This paper will investigate whether low energy impact damage detection can be detected using ECPT and different signal processing algorithms. A new method combining PCA and wavelet transform is proposed to process thermal image sequences of ECPT for impact damages evaluation of CFRP. The PCA method can reduce the dimensionality of datasets and transform the original measured data into new uncorrelated variables It can improve the ability of detecting the deep defects and micro defects. Integration of PCA and wavelet transform have optimal time-spatial scale feature and make up each other effectively to strengthen the detectability of small impact damage.
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