An infrared thermoelastic stress analysis investigation of single lap shear joints in continuous and woven carbon/fiber epoxy composites

A full-field thermoelastic stress analysis infrared method is used to study the damage initiation and progression in prepreg uni-tape and woven carbon fiber/epoxy composite single lap joints. Two loading schemes are studied to detect the damage initiation in these joints. In the first scheme the loading is monotonically increased with cyclic loading performed at the holding times. In the second scheme, the loading is increased gradually and then decreased, followed by cyclic loading at the holding time. The thermoelastic stress analysis infrared measurements show that both methods are capable of predicting the onset of damage at the bonded joint. The observed measurements indicate non self-similar crack growth or non-uniform crack extension along the bondline. Microstructural analysis is performed at the locations where damage is believed to have occurred for specimens extracted before final failure. The investigation confirms the capability of this method to capture early stages of damage in bonded joints.