Stiffness degradation and fatigue damage evolution in treated ramie fibre-reinforced epoxy composites

• Surface modifications of ramie fibre by alkali treatment and analysis of the effect on the fibre. • Investigations of fatigue behaviour of Ramie/Epoxy natural fibre composites. • Analysis of fatigue damage growth mechanism of Ramie/Epoxy by monitoring residual stiffness. The service life of the engineering structures and materials depends on the cyclic loading applied or acting at different operating conditions. This study investigates the fatigue performance of Ramie fibre-reinforced epoxy composites at various stress levels (0.6, 0.7 and 0.8). The bidirectional Ramie fibre was treated with Potassium Hydroxide (KOH) to improve the surface characteristics and interfacial bonding with the epoxy matrix. The Ramie/Epoxy laminates were fabricated using the hand lay-up technique followed by the vacuum bagging technique. The effect of fibre treatment on Ramie fibre was studied by performing Fourier-transform infrared spectroscopy (FTIR) analysis and X-ray diffraction (XRD) on the untreated and treated fibres. The FTIR and XRD results showed the removal of hydroxyl groups and non-cellulosic amorphous materials from the fibre surface. The stress-strain curve was plotted to evaluate the mechanical behaviour of the composite, and the average tensile strength and modulus of the composite were noted to be 83.54±3.98 MPa. and 5.36 ± 0.15 GPa, respectively. During the digital image correlation analysis, the localized strain map along the loading direction revealed the failure region and the average Poisson's ratio of 0.40. The stiffness degradation and fatigue damage evolution were analyzed at different stress levels. The stiffness of the Ramie/Epoxy depended on the stress level, and a higher rate of degradation was observed at a stress level of 0.8. The failure surface morphology study using the scanning electron microscope (SEM) showed that the surface treatment had significantly improved the bonding between the fibre and matrix.