As mentioned before, residual stresses are generated due to mismatch of mechanical and thermal properties of fibres and matrix. It seems that residual stresses amplitude is more dependent on CTE of composite components. At a macro-mechanical level, expansion and contraction of different layers with different orientations is the major source of residual stresses. Especially, CTE of a uni-directional ply along the longitudinal direction is much lower than the CTE in the transverse direction, because of the thermal property difference of fibres along these directions. So during the curing and cooling processes, layout of layers with different CTE to each other, results in macro-residual stress induction in composites. In polymer composites, fibres have lower CTE in comparison with the matrix; and during the curing and cooling processes, the matrix has more contraction, therefore a compressive residual stress through fibres and a tensile stress through the matrix are generated at the micro-scale.