The extensive use of carbon fiber-reinforced plastic (CFRP) composite materials in various industries has posed new challenges for conducting effective structural health monitoring and nondestructive evaluation techniques. Based on local defect resonance (LDR), the vibrothermography with narrowband sweep excitation is proposed to detect BVIDs in the CFRP composite. The response spectrum of displacement at the impact crater was collected by a laser Doppler vibrometer, which was used to determine the frequency range of narrowband sweep excitation. The frequency range was further validated by the analysis of local defect resonance for thermal responses, and the sweep duration was also optimized. Subsequently, the proposed vibrothermography was employed to detect BVIDs with varying severity. The impact damage could be efficiently activated and a significant temperature rise was generated in the defective areas, which enhances the temperature contrast of the thermal images and facilitates the quantification of defects.

Introduction

Carbon fiber reinforced polymer (CFRP) composite has excellent mechanical properties, such as high specific strength, low density, fatigue resistance, and corrosion resistance, making it widely used in various industrial fields [1]. However, the laminated structure of CFRP composites makes them susceptible to impact damage. Some of these impact damages are barely visible to the naked eye and often referred to as barely visible impact damage (BVID) [2]. The presence of BVID can degrade the mechanical properties of the material and lead to structural failure of the composite components, so a fast and effective inspecting technique is important to maintain the reliability of the composite structures. Due to the hidden nature of BVID, it is challenging for the commonly used conventional non-destructive testing (NDT) techniques.

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