The Physical Mechanisms Responsible for the Weathering of Epoxy Resins and Glass Fibre Reinforced Expoxy Resins

摘要

The application and development of a number of optical techniques designed to obtain experimental measurements of the internal stress fields present in the matrix phase of epoxy resin based composites is described. The stress fields arise from curing and during the swelling that accompanies water uptake. One experiment enables the radial and tangential components of the stress field present around an individual fibre to be measured using an oblique incidence photoelastic method. Another, particularizing interlaminar swelling, uses thin plate elasticity theory to calculate stresses from the deformation of a microscope cover slip bonded to a unidirectional composite which is immersed in water at room temperature. The third exploits the photoelasticity present in and around short fibres allowing direct comparison of the loss of load transfer between commercially drawn fibres with laboratory grades of different glass fibres exposed to warm water. Computer models have been developed which are capable of accepting the data to give a realistic analysis of states of internal stress anticipated to occur during service. Stress analysis using polarized light has been simplified by representing the changing state of polarization by the Poincare sphere construction. A finite element approach, employed for modelling the stress field normal to the fibre, treats the fibre as purely elastic and the resin matrix as elastoplastic. (Author)