  Ductile metals undergo a considerable amount of plastic deformation before
failure. Void nucleation, growth and coalescence is the mechanism of failure in
such metals. {\alpha}/{\beta} titanium alloys are ductile in nature and are
widely used for their unique set of properties like specific strength, fracture
toughness, corrosion resistance and resistance to fatigue failures. Voids in
these alloys were reported to nucleate on the phase boundaries between {\alpha}
and {\beta} phase. Based on the findings of crystal plasticity finite element
method (CPFEM) based investigation of the void growth at the interface of
{\alpha} and {\beta} phases [1], [2], a void nucleation, growth, and
coalescence model has been formulated. An existing single-phase 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
strain), and phase boundary inclination) on void nucleation, growth and
coalescence are used to formulate the 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 {\alpha}/{\beta} titanium alloy
components is also demonstrated using experimental data.
