A Thermomechanical Study of Stress and Fatigue in Shape-Memory Alloys with Applications to Micromechanical Structures

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CMS 9800006 PI: P. Papadopoulos UC Berkeley ABSTRACT A combined theoretical, experimental, and computational study of polycrystalline shape memory alloys in the presence of general three dimensional stress states and finite kinematics is conducted to better understand their uncertainty in stress response and in fatigue life prediction. The mathematical structure of continuum thermoplasticity is exploited for macroscopic modeling of superelasticity and shape memory effect. Solid -solid phase transitions are associated with yield-like functions while rate type constitutive equations are postulated for the evolution of inelastic strain and hardening like variables. The stress response is derived from a specific free energy function calculated as a weighted average of specific free energies of all active phases plus the free energies associated with the transformations between them. The systems analyzed here have numerous important applications in bioengineering and in the control of composite intelligent structures. ***