Experimental investigation and 3-D modeling of rate-dependent irrecoverable deformation in shape memory alloys
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Active structures composed of Shape Memory Alloys (SMAs) are becoming more prominent in applications with high force/low space design constraints, and the capabilities of numerical models intended to aid to the design process must be expanded. New applications have been proposed which require special high temperature SMAs (HTSMAs) where the operating temperatures can exceed one-third the melting temperature. Such imposed thermal conditions induce rate-dependent irreversible phenomena (viscoplasticity). A new 3-D model for SMAs undergoing viscoplastic deformation is discussed for the first time in this work, and new developments in he experimental investigation and numerical analysis pertaining to rate-dependent irrecoverable inelasticity in SMAs are also addressed. The description of simultaneous phase transformation and viscoplastic deformation requires the development of a theoretical framework able to capture the coupling between the rate-independent ransformation and the rate-dependent creep. The proposed model is based on continuum thermodynamics, where the evolution equations and the hardening functions are properly chosen. While the transformation processes are rate-independent, the evolution equation for the viscoplastic strain is non-homogeneous in time, and rate-dependency is shown. The viscoplastic strain evolution follows Norton's Law, where the rate of creep is dependent on temperature. Implementation in an Abaqus FEA framework is completed using return mapping algorithms specially derived to consider simultaneous transformation and viscoplastic yielding. The model is experimentally calibrated and a cylindrical compression specimen composed of HTSMA and undergoing simultaneous ransformation and viscoplastic yield is modeled in a 3-D environment. This analysis represents the first ample of 3-D viscoplastic SMA analysis found in the literature. 2009 SPIE.
name of conference
Behavior and Mechanics of Multifunctional Materials and Composites 2009