Investigations on the Influence of High Pressures on the Curing Behaviour and Material Properties of Composite Structures for the Development of a Material Model

Abstract

Former investigations have shown, that high pressure influences the cure behaviour and mechanical properties of epoxy resins. Simulation approaches for manufacturing processes of composite parts developed so far do not consider pressure dependency, since process pressure is generally low. In recent developments, curing of epoxy resin under high pressure occurs, for example during the high-pressure resin transfer moulding (HP-RTM) process. In this study, a model approach is presented, which considers the effect of pressure by augmenting an existing simulation approach using free-volume theory. It could be demonstrated, that a description of the material properties based on the fractional free volume is possible and thus the pressure dependency could be brought into the process simulation via free volume, in theory. In order to verify the practical relevance, experimental investigations were conducted to confirm an effect of pressure on dielectric properties, conversion and glass transition temperature of epoxy resins. An increase of process pressure leads to a higher final degree of cure, glass transition temperature and ion viscosity. The influence of high pressure on mechanical properties, such as elastic modulus or fracture stress could not be proven conducting tensile tests.