Characterisation of the torsional behaviour of titanium metal matrix composite shafts

Titanium Metal Matrix Composites (TiMMC) have been gaining momentum in the aerospace applications in the past two decades. The advantages of TiMMC include superior stiffness-ta-weight and strength-ta-weight ratios, compared to conventional aerospace steels. The low pressure shaft in the aeroengine is one of the components that could benefit from the superior material properties of TiMMC. Potentially, the use of TiMMC could provide a combination of higher torque density (higher torque for a given diameter) and lower weight for these shafts. However, little has been done to investigate the torsional behaviour of TiMMC shafts. This thesis investigates the torsional behaviour of TiMMC shafts with different fibre orientations, through experimental tests. A material database was established for the TiMMC system used for each fibre orientation. Further to that, a comprehensive failure investigation was carried out on the tested specimens in order to understand the failure mechanisms. Samples from the fractured specimens were polished and etched to study their microstructure and internal features. Numerical models were developed to predict the global orthotropic elastic material properties of TiMMC using the unit cell concept. The material properties were then used in the tube models which predict the shear moduli for different fibre orientations. The results were validated with the experimental test results. To minnimise weight, aeroengine shafts aim to have thin walls, which could result in buckling instability. Numerical models were therefore developed, to investigate the buckling behaviour of TiMMC shafts. Hill's potential fun ction in ABAQUS was used, which define the anisotropic yield behaviour, using user-defined stress ratios. As a result of this research, the understanding of the torsional behaviour of TiMMC has been strengthened.EThOS - Electronic Theses Online ServiceGBUnited Kingdo