Failure analysis under fatigue loading of glass fibre reinforced in-situ polymerizable thermoplastic and Bio-epoxy based Composites

• Tension-tension fatigue behavior of glass fiber composites based on the choice of thermoplastic or thermoset matrix materials are comparable. • A difference in stiffness reduction with respect to fatigue loading cycles based on the choice of matrix material was apparent. • Scanning electron microscopy and X-ray CT scan techniques employed extensively to study the failure behavior of the tested composites. • Distinct visual difference between failure modes of each lay-up configuration observed at the macro level. • Micro level failure mechanisms dependent on fiber-matrix interaction influence the fatigue behavior of the composites evaluated. This experimental study investigates the fracture and failure mechanisms of glass fiber reinforced polymer matrix composites fabricated using an in-situ polymerizable thermoplastic and a bio-based epoxy matrix subjected to tension-tension fatigue loading. For both material systems, fatigue tests resulted in linear S-N curves for the 0°, 90° and Quasi-Isotropic (QI) laminates and non-linear (power law) S-N curves for the ±45° and ±30° laminate configurations. However, the main focus of the study was on the failure mechanisms for both the low-cycle and high-cycle fatigue loading regimes. At the macro level, the effect of the different matrices on the characteristic failure mode was generally minimal with all lay-ups exhibiting distributed damage throughout the gauge region except for the 90° laminates where damage was highly localised. However, micro level analysis conducted using SEM and elemental composition analysis revealed significantly different failure mechanisms in the vicinity of the fibre matrix interface for the bio-epoxy (interfacial) and the thermoplastic (cohesive). Overall, both matrices show promise in terms of fatigue performance under benign laboratory conditions and as a stepping stone towards achieving more sustainable matrix options for offshore renewable energy structures in the future.