Evaluation of thermal residual stresses of thin-walled laminated composite pipes to characterize the effects of mandrel materials and addition MWCNTs

This research focuses on finding the effects of the addition of multi-walled carbon nanotubes (MWCNTs) and using various mandrel materials on the ply-level thermal residual stresses of thin-walled laminated filament-wound composite pipes. To accomplish this objective, a few specimens were made by considering two various weight fractions, containing 0 and 3%, for MWCNTs and two various mandrel materials, containing aluminum and steel. This study employed the incremental hole drilling method using integral inverse solution for measuring the thermal residual stresses within the structure. This method contains simulation and experimental parts, which both were explained in details entirely. This paper presents analytical discussions and the experimental results to clarify achievements. The results confirmed that adding MWCNTs, as a thermal expansion compensator, to the epoxy matrix modifies the thermal behavior of the epoxy matrix and reduces the thermal residual stresses in the composite pipes. Also, the results show that the residual stresses are strongly affected by the mandrel thermal expansion coefficient. In this case, for example, the specimen manufactured by the steel mandrel experiences less residual stresses compared to which manufactured by the aluminum mandrel.