Experimental Investigation on Impact Damage Detection in CFRP Pipes using Low-power Ultrasonic Thermography with Sweep Excitation

The growing demand for carbon fiber reinforced polymer (CFRP) pipes in industry and their susceptibility to impact damage have led to great focus on damage detection in these structures. This paper proposes a method for detecting impact damage in CFRP pipes using low-power ultrasonic thermography with sweep excitation. The bottom of ultrasonic transducer was designed into a curved surface to improve its coupling to the composite pipes. In accordance with the attributes of local defect resonance (LDR), the frequency band was ascertained by analyzing the displacement spectrum at the site of impact damage. The LDR frequencies were further validated from the thermal responses of ultrasonic thermography inspection and finite element analysis of the specimen eigenfrequencies. Finally, the method was used to detect various impact damage on CFRP pipes. Since the LDR frequency at the defect is covered by the frequency range of the narrowband sweep excitation, impact damages can be efficiently activated, resulting in an obvious temperature rise.