Transverse behaviour of a unidirectional composite (glass fibre reinforced unsaturated polyester). Part I. Influence of fibre packing geometry

Abstract

A micromechanical investigation of the transverse creep behaviour of unidirectionally reinforced glass fibre composites with an unsaturated polyester as matrix is presented. A previously established nonlinear viscoelastic model of the deformational behaviour of the unsaturated polyester matrix is used in the numerical calculations. The matrix model includes effects of physical ageing of the resin and, in its general 3D-formulation, is able to describe time-dependent lateral contraction. The latter has been modelled by adopting two distinct constants: a creep contraction ratio and an instantaneous elastic Poisson's ratio. The 3D-model has been implemented into a finite element (FEM) package. The excellent agreement obtained between the FEM calculations and experimentally obtained strains for various model (uniaxial and multiaxial) loading situations lends confidence to the ability of the model to describe the time-dependent behaviour of the unsaturated polyester under general 3D loading situations [Zhang, Ernst, Brouwer, 1997. A Study of Nonlinear Viscoelasticity, Part 2. 3D Theory. Mech. Mater. 26, 167–195]. The model predictions are compared with experimentally obtained transverse strains of filament wound tubes, loaded in transverse tension. It is shown that the fibre packing geometry plays a dominant role in the model prediction results. The traditionally adopted packing geometries do not meet the requirements in practice. The rectangular packing geometry for instance lacks transverse isotropy, which is unrealistic for the composite considered. The hexagonal packing geometry exhibits poor accuracy in predicting the global strain response, which is ascribed to the inability of this packing geometry to deal with the experimentally observed inhomogeneous distribution of fibres in the transverse plane of the composite. To eliminate these shortcomings, new geometries are presented. They show good agreement with experimental data and moreover reveal a detailed stress and strain distribution and redistribution over time on a local level.