Abstract
The effect of ionomer thickness on mode Ⅱ interlaminar fracture toughness was investigated for ionomer - interleaved CF / epoxy laminates. Laminates were fabricated with Toho UT500 / 111 prepregs. Ethylene based ionomer, which forms the toughened interphase at the ionomer / base lamina interfaces, was used as an interleaf material. Thickness of ionomer film was selected as 25,100 and 200 μm. Mode Ⅱ fracture toughness tests were carried out using end notched flexure specimens. Fracture toughness values were much improved by interleaving the ionomer films. The fracture toughness values increased linearly with increasing the ionomer thickness. This thickness effect of the ionomer interleaf differs from that under mode I loading where the presence of ionomer is more effective than the increase in its thickness. Microscopic observation revealed that the main crack path was inside the toughened interphase and at its interfaces. Plastic deformation of the ionomer expanded through the whole ionomer region in the thickness direction. Difference in the thickness effect on fracture toughness between under mode I and Ⅱ loadings were discussed from the view point of the size of the plastically deformed region.
