Delamination fracture toughness of continuous glass-fiber/epoxy composites for structural applications

This paper presents experimental results of delamination fracture toughness tests on glass-fiber/epoxy composites which are manufactured in a novel Compression Resin transfer molding (CRTM) process in comparison to the performance of a well-studied RTM reference process. The examined laminates are built out of six plies, with a plain weave fiber orientation. 90% of the fibers are in longitudinal direction and 10% are perpendicular woven in. The influence of the process regarding interlaminar fracture toughness is tested under pure mode I (DCB), pure mode II (ENF) and mixed mode loading (MMB). The aim of this study is to establish a semi-empirical criterion to derive the interlaminar fracture toughness of all mixed-mode ratios using the pure mode I or II loading fracture toughnesses. It has been found, that the materials performance for both processes are comparable, however the fracture behavior is strongly influenced by the fabric structure. The examination of the laminates polymer system showed a strong R-curve behavior for mode I and mode II loading. It was possible to establish a semi empirical criterion that shows good agreement with the experimental results.