Influence of thermally induced microstress and microstructural randomness on transverse strength of unidirectional composites

Abstract

An investigation is performed into the interaction between thermally and mechanically induced stresses and their relation to failure in a unidirectional composite under transverse tension and longitudinal shear. Multiple realizations of periodic unit cells with randomly positioned fibers are used. It is found that for microstructures with close fiber spacing, thermally induced stresses from cooling after cure tend to relieve the critical mechanically induced stress in the matrix for transverse tensile load, while they tend to worsen the critical stress for microstructures with space between fibers. Matrix strength properties are obtained through the solution of an inverse problem and are then used to perform progressive failure analyses at various temperatures. These analyses indicate that for random microstructures with closely spaced fibers, cooling after cure tends to increase the transverse tensile strength of the unidirectional composite, while cooling tends to weaken models using a hexagonal microstructure.