THESIS
2019
xii, 81 pages : illustrations ; 30 cm
Abstract
For a better understanding of martensitic transformation, a novel phase field model is built
up to simulate the evolution of the microstructures in shape memory alloys. The model is set in
the energetic framework so that the kinetic equations and mechanical equilibrium equations are
defined to construct the constitutive model for symmetry-breaking phase transformation. The
proposed free energy density function involves the bulk elastic energy and interfacial energy.
The latter describes the energy of diffusive interfaces with a specific phase field ansatz. In order
to capture the effects of different interfacial energies of austenite-martensite interfaces on twin
boundaries, the order parameters are introduced in a hierarchical manner. Considering the
solution to crystallographi...[
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For a better understanding of martensitic transformation, a novel phase field model is built
up to simulate the evolution of the microstructures in shape memory alloys. The model is set in
the energetic framework so that the kinetic equations and mechanical equilibrium equations are
defined to construct the constitutive model for symmetry-breaking phase transformation. The
proposed free energy density function involves the bulk elastic energy and interfacial energy.
The latter describes the energy of diffusive interfaces with a specific phase field ansatz. In order
to capture the effects of different interfacial energies of austenite-martensite interfaces on twin
boundaries, the order parameters are introduced in a hierarchical manner. Considering the
solution to crystallographic equations of martensite, we propose a kinematic model for
transformation strain tensors. Besides, the bulk energy is given in a way to avoid the unphysical
shift of equilibrium state of order parameters. To make the phase field model capable of
simulating martensitic transformation under different temperature conditions, the proposed free
energy function explicitly incorporates temperature and latent heat.
We numerically solved the kinetic equations based on the proposed constitutive model,
which is implemented by the finite element solver COMSOL. Different simulations are
performed under various boundary conditions. The numerical results are consistent with the
experimental observations and the solution to crystallographic equations of martensite. Through
a series of simulations, the effects of crystal orientation, boundary condition, temperature and
loading rate on the evolution of microstructures and thermomechanical properties of shape
memory alloys are discussed.
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