Effect of layer thickness of prepreg on static and dynamic flexural properties of continuous carbon fiber reinforced polyamide 6

Abstract

The effect of layer thickness of prepreg on the static and dynamic flexural properties of quasi-isotropic carbon fiber reinforced polyamide 6 laminates were investigated. The layer thickness of each ply was set to 40, 80 and 120 µm by using thin-ply prepreg with a thickness of about 40 µm made by tow-spreading technology. Four-point flexural tests were carried out to evaluate the static flexural properties of the laminated materials. The results showed that the flexural strength and modulus did not change much as the layer thickness change. The delamination at interlaminar was interestingly inhibited with decrease of layer thickness. Charpy impact strength evaluated as the dynamic flexural properties was affected by the layer thickness depending on the impact direction. In the impact test where the applied load was parallel to the laminates (edgewise test), the Charpy impact strength was almost unaffected by the layer thickness change. In contrast, Charpy impact strength increased with increasing layer thickness where the applied load was normal to the laminates (flatwise test). In the observation of the fracture appearance after edgewise test, the fiber fractures were observed independent of the layer thickness. Meanwhile, the occurrence of the cracking and delamination at interlaminar were effectively suppressed with decrease of layer thickness in the specimen after flatwise test. The delamination at interlaminar progressed in the in-plane direction with increasing layer thickness, resulting in large-scale delamination. As a result, a large amount of fracture energy could be absorbed. In conclusion, the layer thickness of the laminate is an important material design factor for controlling the impact properties of the composite materials.