عنوان مقاله [English]
Due to the natural inconsistency of the mechanical and thermal properties of fiber and matrix, residual stresses are introduced during the curing process of fibrous polymer composites. Considering a high Youngs modulus and the negative coefficient of thermal expansion (CTE) of carbon nanofibers (CNFs), the addition of CNFs into the matrix makes its properties closer to reinforcement, and this reduces residual stress in laminated polymer composites. In this research, a novel method to decrease the deformed shape of cross ply un-symmetric laminated composites, by adding vapour grown carbon nanofiber, is proposed. To this end, first, using thermo mechanical analysis (TMA) and tensile test methods, the coefficient of thermal expansion and the Youngs modulus of vapour grown carbon nanofiber reinforced epoxy are measured. The characterizations showed a significant decrease in the coefficient of thermal expansion and a slight increase in the Youngs modulus of the matrix. Then, using the sonication technique, as well as the hand layup method, vapour grown carbon nanofiber/carbon fiber/epoxy cross ply laminated composites are fabricated in different vapour grown carbon nanofiber weight loadings, and the percentages of deformations are measured carefully. The results show that adding 1 wt of vapour grown carbon nanofiber to the composites can reduce the out of plane deformation of un-symmetric laminates up to 48%. Finally, the finite element method and the classical lamination theory (CLT) are used to validate the experimental observations. The results of this comparison show good agreement between the modeling and the experimental results. The results indicate that the addition of low contents of CNF causes the coefficient of thermal expansion of the matrix to decrease and the matrix Youngs modulus to increase, which, in turn, leads to a considerable reduction in micro and macro thermal residual stresses. This reduction will decrease the unwanted deformed shape of the cross ply un-symmetric laminated composites.