PRESSURE INFLUENCE DURING CURING ON THE MECHANICAL PROPERTIES OF EPOXY RESIN COMPOSITES AT HIGH STRAIN RATES

摘要

Fibre reinforced plastics are used in many applications due to their good strength to weight ratio. Carbon fibre reinforced plastics (CFRP) with epoxy resin matrix are often used in automotive applications. The crash behaviour and thus the behaviour of the composite at high strain rates is of great importance for this application. Composites are produced in automatable processes such as Resin Transfer Moulding (RTM) or in autoclave processes with prepregs, where the process pressures are increased. The influence of the process pressure on the curing behaviour and therefore on the material properties has, however, only been investigated to a limited extent in the literature. The aim of this work is to investigate if even a small pressure difference of 5 bar, which is common in the RTM process, leads to changes in material properties under high strain rates as occurring in the crash case in automotive engineering. Izod notched bar impact tests on epoxy resin specimens and tensile tests with high strain rates on CFRP are carried out. The notched bar impact tests show a significant increase of the notched bar impact strength with an increased pressure. The fracture surfaces also differ between the different pressure states. The specimens cured under increased pressure show significantly rougher fracture surfaces, which indicate a changed fracture behavior. During fracture, significantly more energy is absorbed. The tensile tests with a high strain rate show that the pressure influence also occurs in CFRP with fibres. A significantly higher energy absorption during fracture is determined here. This work shows that the process pressure during curing has a significant influence on the behaviour of CFRP under high strain rates. Therefore, it is possible to directly influence the properties under high strain rates by process parameters in the RTM process without adding viscosity increasing additives.