A simplified fatigue characterization of defective CFRP laminates with infrared thermography

Fiber misalignment and out-of-plane waviness are defects encountered in composite material laminates. These defects are particularly prone to occur when adapting the laminate to angular or complex geometries. Using these defective laminates in aerospace applications can undermine their structural integrity and impact their mechanical properties. This work involves a study of applying infrared thermography techniques to estimate the fatigue limit based on the energy dissipated during tensile testing. Defect-free CFRP laminates and laminates with several out-of-plane waviness distributed along the sample and through the thickness are tested at various stress levels. Estimation of their fatigue limit using thermography is performed, and the results show a significant agreement to those obtained through S-N curves, with less than 2% error for defect-free specimens and 13% for defective ones. A reduction in mechanical properties and service life is observed in the material with defects compared to defect-free material, with a decrease of 16% of the ultimate strength and 40% of the fatigue limit. The study supports the application of thermography as a simple and rapid technique to detect and locate this type of defect and characterize the fatigue limit of the CFRP laminate.