Early-stage fatigue evaluation of CFRP laminates using microscale lock-in thermography based on laser-spot-periodic-heating method

• Published in: Infrared physics & technology Vol. 126; p. 104323
• Main Authors: Fujita, Ryohei, Katsukura, Kotaro, Nagano, Hosei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2022
• Subjects: CFRP; Fatigue; Laser-spot-periodic-heating-method; Lock-in thermography; Non-destructive inspection; Thermal diffusivity; Fatigue; Non-destructive inspection; Thermal diffusivity; Lock-in thermography; Laser-spot-periodic-heating-method; CFRP
• ISSN: 1350-4495; 1879-0275
• DOI: 10.1016/j.infrared.2022.104323

•Early stages of fatigue loading on CFRP lead to the decrease of the effective thermal diffusivity De up to 17% compared with the undamaged sample.•Proposed De measurement model using the lock-in thermography has the capability to evaluate the fatigue condition of CFRP.
In this paper, the evaluation method of early-stage fatigue was proposed for carbon fiber reinforced plastic (CFRP) laminates based on a laser-spot-periodic-heating method using a lock-in thermography. The effective thermal diffusivity in the out-of-plane direction was measured from the periodic thermal response generated on the side surface of the CFRP. The validity of this method was demonstrated by evaluating the dependence of the effective thermal diffusivity against the fatigue load cycles. Fatigue tensile tests were conducted with load cycles of 103, 104, 105, and 106 for each sample. The side surface observation of the laminated sample using an optical microscope confirmed that these samples did not have transverse cracks therefore the samples were in the early stages of fatigue. The effective thermal diffusivity was calculated by fitting a heat conduction model to the measurement results. The theoretical curve matched well with the measured results. As a result, the effective thermal diffusivity tended to decrease with the number of loading cycles, indicating that this method has the capability to evaluate early-stage fatigue.