Agboola, Babatunde Omogbolahan (2015-07). Development and Implementation of Configurational Forces based Constitutive Phase Field Models for Shape Memory Alloys. Doctoral Dissertation.
Thesis
Continuum thermodynamic constitutive phase field models are developed to simulate the rate dependent, thermomechanical response and precipitate formation in shape memory alloys (SMAs). The two models are based on the application of the balance of configurational forces, a scalar order parameter (a phase field) and atomic concentration to extend standard continuum thermodynamics approach. Constitutive field equations that capture the kinetics of solid-solid martensitic phase transition in SMA and the diffusion mediated precipitate formation in an elastic solid are developed. The coupled set of thermodynamically consistent field equations results from balance of configuration forces, balance of linear momentum, balance of energy and balance of atomic species mass. The field equations capture the kinetics of phase transition, deformation and elastic wave, heat transfer and atomic diffusion respectively. The first model is thermomechanical and is used to simulate the macroscopic response of SMA such as pseudoelasticity; transformation induced pseudo-creep, stress relaxation as well as the effect of cooling rate on mechanical and thermally induced phase transformation of SMA. The second model couples diffusion with elasticity to simulate growth and coarsening of precipitate and experimentally observed concentration depletion near the precipitates Results of the simulations of the macroscopic SMA response are in very good agreement with experimental observation. Simulations suggest that rate dependent and complex thermomechanical response of SMA are due to the interaction of an inherent time scale ( as well as length scale) of phase transformation, introduced through the balance of configurational forces, with other time scales. This work contributes to improved SMA modeling, scientific understanding and design. In particular, for aerospace application under stringent requirement and severe environmental conditions. Contribution of fundamental use of balance of configurational forces to extend continuum thermodynamic modeling is demonstrated. Results of the simulations of the macroscopic SMA response are in very good agreement with experimental observation. Simulations suggest that rate dependent and complex thermomechanical response of SMA are due to the interaction of an inherent time scale ( as well as length scale) of phase transformation, introduced through the balance of configurational forces, with other time scales. This work contributes to improved SMA modeling, scientific understanding and design. In particular, for aerospace application under stringent requirement and severe environmental conditions. Contribution of fundamental use of balance of configurational forces to extend continuum thermodynamic modeling is demonstrated.
