Influence of the free surface on the thermal stresses in unidirectional composites

Thermal stresses in a continuous carbon fiber reinforced polymer matrix composite are determined using the finite element method (FEM) and 3-D FEM models. The zone close to the free surface (the end zone) and the zone far from the free surface (the inner zone) are analyzed. These two zones have substantially different stress characteristics. The analysis of the end zone revealed significant radial and hoop stress concentrations. These concentrations are sensitive to meshing indicating the stress singularity localized at the free surface on the fiber/matrix interface. Qualitative investigations of the effect of meshing on the stress concentration permits determination of the order of singularity which, in general, depends on the composite parameters. It is shown that this order is mostly effected by the transverse Young's modulus and the Poisson's ratio of the fiber. (C) 1997 Elsevier Science Limited.