A Multiscale Constitutive Model for Metal Forming of Dual Phase Titanium Alloys by Incorporating Inherent Deformation and Failure Mechanisms

Ductile metals undergo a considerable amount of plastic deformation before failure. Void nucleation, growth and coalescence is the mechanism of failure in such metals. 𝛼 – 𝛽 titanium alloys are ductile in nature and are widely used for their unique set of properties such as specific strength, fracture toughness, corrosion resistance and resistance to fatigue failures. Voids in these alloys have been reported to nucleate on the phase boundaries between 𝛼 and 𝛽 phase. Based on the findings of crystal plasticity finite element method (CPFEM) investigations of the void growth at the interface of 𝛼 and 𝛽 phases, a void nucleation, growth, and coalescence model has been formulated. An existing singlephase crystal plasticity theory is extended to incorporate underlying physical mechanisms of deformation and failure in dual phase titanium alloys. Effects of various factors (stress triaxiality, Lode parameter, deformation state (equivalent stress), and phase boundary inclination) on void nucleation, growth and coalescence are used to formulate a phenomenological constitutive model while their interaction with a conventional crystal plasticity theory is established. An extensive parametric assessment of the model is carried out to quantify and understand the effects of the material parameters on the overall material response. Performance of the proposed model is then assessed and verified by comparing the results of the proposed model with the RVE study results. Application of the constitutive model for utilisation in the design and optimisation of the forming process of 𝛼 –𝛽 titanium alloy components is also demonstrated using experimental data.