1 Department of Wind Energy, Technical University of Denmark2 Composites and Materials Mechanics, Department of Wind Energy, Technical University of Denmark
The main objective of this experimental investigation was to evaluate the changes from accelerated ageing on selected properties of carbon fibre/polyamide 6 composites based on hybrid yarns. In this study, two types of mechanical tests were performed to measure the environmental influence on the material properties. They are three-point bending to measure the flexural strength and stiffness, and short beam three-point bending to measure the interlaminar shear strength. The 10-mm-thick quasi-isotropic carbon fibre/polyamide 6 composites with 52% volume fraction of carbon fibre to be tested were manufactured by autoclave consolidation. The test samples were dried, and subsequently exposed to 60 and 100% relative humidity at different lengths of time up to 2500 h, followed by drying at 23 and 50% relative humidity. Few samples were additionally completely dried at 70 in vacuum for 21 months. Tests were also performed on as manufactured and dried material at low temperature (–45) and high temperature (115). The measured mechanical properties decreased with exposure time at 60 and 100% relative humidity. Both the bending stiffness and the strength degrade to a level of about 65%, whereas interlaminar shear strength drops to about 87% of the property values of the unexposed (initially dried) material. The bending stiffness and strength at −45 are about 87% of the properties at room temperature, whereas at 115 the stiffness drops to 75% and the strength drops to 60% of the properties at room temperature. The interlaminar shear strength values also drop to about 75% at both −45 and 115. Extreme temperatures and long-time exposure to humidity of quasi-isotropic carbon fibre/polyamide 6 laminates can thus reduce the bending stiffness and strength by up to 35% and the interlaminar shear strength by up to 25%.
Journal of Composite Materials, 2014, Vol 48, Issue 21, p. 2551-2565