Micro-mechanical model of thermal expansion/contraction for damaged fiber reinforced composites

Considering damages of matrix micro-cracks and fiber/matrix debonding, the thermal expansion/contraction theoretical model of fiber reinforced composite (FRC) was developed by using micro-mechanical method. In the model, differences of opening and closing conditions of micro-cracks in different orientations, both in matrix and fiber/matrix interface corresponding to heating and cooling and their effects on average coefficient of thermal expansion/contraction (CTE/CTC) were explored. The model has also taken the ununiformity of stresses in micro-scale into account. Micro finite element model was built to validate the theoretical model. The results reveal that CTE and CTC of damaged FRC are not identical and their discrepancy depends on damage modes. The matrix micro-crack damage could promote transverse CTE of FRC higher than nondestructive material's and decrease transverse CTC lower than nondestructive material's, however it has little effect on longitudinal CTE/CTC. Fiber/matrix interface debonding could bring notable reduction of longitudinal CTC, but be ignorable to transverse CTC.