Within the thermodynamics of irreversible processes and the concept of in ternal state variables, a general phenomenological theory of coupled damage-elasto- (visco)plasticity at small strains is given. The state variables (external and internal) are considered to evolve phenomenologically according to competing processes between ther mal and elastic properties, strain hardening (isotropic and kinematic) and continuous iso tropic damage. Using the classical isotropic Continuum Damage Mechanics (CDM), a new energy based coupling model is used to introduce the effect of the damage on elastic and anelastic (hardening) behaviors. Both time independent (plasticity) and time depen dent (viscoplasticity) cases are discussed in details.
In order to treat scoliosis, a thermo-mechanical behavior study of shape memory alloy bone staple has been proposed. A pre-stretched shape-memory-alloy bone staple, which has been heated above the transition temperature, provides greater compressive force upon insertion between two vertebrae and allows the control of idiopathic scoliosis development. Until now, the optimal design has not been reached due to the lack of appropriate design tools for shape memory alloy devices. In this paper, a shape memory alloy bone staple model is proposed by developing a user subroutine UMAT based on Boyd et al.[1] unified thermodynamic shape memory alloy constitutive law using the finite element analysis software, ABAQUS. The numerical results for superelastic and shape memory effect under the tensile and three-point bending tests are presented. Simulations of the shape memory effects and force generation of the shape memory alloy staple are also shown.
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