Fatigue crack growth and delamination mechanisms of Ti/CFRP fibre metal laminates at high temperatures

Ti/CFRP (titanium/carbon fibre reinforced polymer) fibre metal laminates (FMLs) are composed of titanium sheets and carbon fibres reinforced PMR (polymerization of monomeric reactants) type polyimide resin. Due to the outstanding heat resistance of the material, it can be used in hypersonic aircraft applications. Fatigue cracks in the metal layer and delamination at metal/fibre interface may occur in long-term high-temperature use processes. However, the behaviour of the fatigue failure at high temperatures has not been investigated. A temperature-dependent equation has not been presented to predict the crack growth behaviour at high temperatures. In this study, to investigate the crack propagation and delamination behaviours, fatigue crack growth rate tests using tension-tension loads at 25 degrees C, 80 degrees C, 120 degrees C, and 150 degrees C were conducted in accordance with ASTM E647-15e1. The results indicated that the variation in fatigue crack growth rate could be described by a modified temperature-dependent Paris equation. Interfacial strength and tensile strength may influence fatigue failure at high temperatures. Hence, these strength values were also obtained to analyse the mechanism of fatigue behaviour. The delamination area increased exponentially with temperature due to the weakening of the Ti/CFRP interface, and delamination was invariably generated on the microcracks of the titanium layers.