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Title: Development of improved numerical techniques for high strain rate deformation behaviour of titanium alloys
Author: Cousins, Benjamin Thomas Spencer
ISNI:       0000 0004 6496 313X
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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Within the aerospace industry, the reduction of costs associated with operation, manufacture and development of gas turbine engines is a primary objective. Component and assembly design optimisations can satisfy weight reductions which correspond to operational and manufacturing cost reductions. Development cost can be reduced by implementing additional numerical validation stages as an alternative to experimental validation alone. Therefore, the overarching purpose of this research is the development of a computationally efficient constitutive modelling tool, which predicts the macroscopic deformation and failure of fan system components and assemblies during dynamic and highly non-linear thermo-mechanical loading. At the macroscopic scale a series of physical deformation and failure phenomena have been identified from the literature which are necessary for accurate representation of the dynamic behaviour of Ti-6Al-4V. Across the surveyed literature these capabilities have not been implemented together within a single constitutive framework prior to the commencement of this research. Experimental support provides validation data for the subsequent constitutive modelling activities, whilst also demonstrating the importance of strain-rate sensitivity, tension-compression asymmetry and anisotropic behaviour associated with texture orientation in Ti-6Al-4V. Numerical studies were also conducted to develop a robust procedure for rapid assimilation of uni-axial experimental data within constitutive benchmarking models, for development purposes. Further parametric studies of sub-component plate impact benchmarks revealed several limitations within the commercially available solutions. These limitations are related to mesh sensitivity and damage evolution. A technique has been proposed which couples damage evolution and imposes a directional length-scale. This provides enhanced mesh insensitivity and damage evolution rate control. However, a single damage evolution mechanism was demonstrated to be insufficient when representing shear damage mechanisms in uni-axial and multi-axial loading regimes. Therefore, an additional damage mechanism has been developed and coupled with the mesh sensitivity and localisation technique. The resulting cumulative and competitive damage evolution and localisation capabilities reflect the localisation characteristics observed in the literature. The variability of alloy manufacture and the subsequent macroscopically observed behaviour remain a limitation within an isotropic framework. This has motivated the development of both asymmetric and anisotropic formulations, integrated within the newly proposed multi-mode damage localisation framework. The ability of the newly implemented non-isotropic framework successfully provides both asymmetric yielding and hardening capabilities and anisotropic evolution. These developments have been demonstrated against experimentally obtained results for validation and calibration purposes. Together these capabilities allow for accurate representation of a wide range of macroscopically observable phenomena based upon micro mechanical mechanisms.
Supervisor: Petrinic, Nik Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Constitutive Modelling ; High Strain Rate