Long-term creep behaviour of E-glass/epoxy composite: Time-temperature superposition principle

Abstract

Creep behaviour of an epoxy matrix composite with a similar arrangement of composites used in a root joint of a wind turbine blade is investigated in this research. The vacuum infusion process was used to manufacture the composite. Due to the linearity of the viscoelastic behaviour of the composite, the time-temperature superposition principle (TTSP) is applied by using an activation energy shifting method to predict long-term creep behaviour. The activation energy (ΔH) is determined to be 281 kJ mol⁻¹. The calculated shift factor in generating the master curve at the reference temperature of 20°C is 4.75 for a 50°C-creep curve and 7.3 for a 70°C-creep curve. Under operating conditions of the root joint, namely at 20°C/40 MPa, the creep compliance is determined to be 0.63 × 10⁻¹² Pa⁻¹ within 27.8 h (10⁵ s) and increases to 8.6 × 10⁻¹² Pa⁻¹ within 10 years (10^8.5 s). The creep compliance master curves at 20°C/40, 100 and 300 MPa within 1157 days (10⁸ s) are determined to be 7.1 × 10⁻¹², 12.5 × 10⁻¹² and 18.3 × 10⁻¹² Pa⁻¹, respectively. Scanning electron microscopy examination shows cusps, scarps and pull-out of fibres.