Hygrothermal ageing effects on failure behaviour of fibre-reinforced polymer composite materials under in-situ SEM testing
Indraneel R. Chowdhury, P. Sampath Rao, Noel P. O’Dowd, A.J. Comer
Abstract
This study aims to analyse the effects of hygrothermal ageing on mechanical properties, weight gain phenomena, and failure mechanisms of non-crimp fabric (NCF) based fibre-reinforced polymer (FRP) epoxy composites following immersion in two different aqueous media – deionised water and seawater at 35 °C until complete saturation. A comparative analysis has been performed between the effect of hygrothermal ageing on moisture absorption characteristics, flexural properties, and corresponding failure mechanisms of NCF basalt FRP and NCF E-glass FRP composites with similar fibre-volume fraction of approx. 54 %. Specimens were tested in-situ using a JEOL JSM-5600 scanning electron microscope (SEM) fitted with a 3-point bend test fixture. Overall, NCF basalt FRP composites demonstrated relatively lower moisture absorption characteristics than NCF E-glass FRP composites in deionised water and seawater. For both NCF basalt and NCF E-glass, moisture ageing significantly affected the flexural strength of composites. NCF basalt FRP demonstrated a reduction of approx. 30–35 % in flexural strength while for NCF E-glass, the reduction in flexural strength was relatively higher ranging to approx. 35–40 %. Flexural modulus of NCF basalt FRP was not significantly affected while for NCF E-glass, a reduction in flexural modulus by approx. 15 % was observed. However, during in-situ SEM testing, the failure mechanisms of moisture-aged NCF basalt and NCF E-glass FRP composites were similar, where failure initiated in the form of fibre/matrix debonding in the 90° sub-ply at the bottom ply on the tension side, but final failure took place due to fibre kinking in the 0° sub-ply of the top ply on the compression side. • Non-crimp fabric (NCF) based fiber-reinforced polymer (FRP) composite materials (both NCF basalt and NCF E-glass) immersed in deionised water demonstrated lower moisture content and diffusion coefficient than NCF FRP composites immersed in seawater. • Moisture absorption of NCF E-glass FRP composites was relatively higher than NCF basalt FRP composites immersed in each aqueous media. • In-situ scanning electron microscopy (SEM) based mechanical testing technique helped in real-time monitoring of failure propagation in FRP composite materials. • Damage in NCF FRP composites under 3-point bend loading initiated in the form of fiber/matrix debonding on the tension side, but final failure took place due to fiber kinking on the compression side.