Polyamide Carbon Fibre Filled Composite Ageing Characterization in Conventional Automotive Fluids

Abstract

The use of carbon fibre-reinforced plastic technology is steadily gaining traction in the modern automotive industry as a lightweight alternative to conventional materials. The versatile chemical resistance of polyamide resins combined with the high strength properties of carbon fibre filler content aims to meet this growing need in the industry. By employing a number of accelerated and amplified ageing techniques, this work hopes to assess the resilience of carbon fibre-reinforced polyamide composites in a variety of foreseeable chemical, temperature, moisture, and stress environments. The resins included in this characterization study include polyamide-6 (PA6) and polyamide-6,6 (PA6/6). The carbon fibre-reinforced composite specimens are subject to long term immersion in commercial automotive fluids at room and elevated temperatures. Results show that the mechanical properties of both polyamide resins are sensitive to windshield washer fluid exposure, regardless of temperature. The significant drop in glass transition temperature and greater elongation at break confirmed a plasticization effect. The Young’s modulus and tensile strength experienced a loss of approximately 40% at saturation. Elevated temperatures resulted in increased fluid sorption rates of antifreeze and E-20 gasoline into the PA6 composite specimens. Likewise, a corresponding drop in PA6 composite mechanical properties was noted for the antifreeze and E-20 gasoline at elevated temperatures. The mechanical properties of the PA6/6 composite were largely retained in all tested automotive fluids, except windshield washer fluid, at elevated temperatures. The effect of absorbed fluid on mechanical properties tended to increase with higher fibre loadings for the PA6/6 composite and lower fibre loadings for the PA6 composite. Finally, a single parameter acoustic emission testing technique was employed to assess internal damage of stressed PA6 composite specimens exposed to different temperature and humidity levels. However, there was no discernible correlation between environmental stress conditions and internal damage for short term exposure times.