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Modeling of the Mechanical Behavior of Shape Memory Alloys under Cyclic Loading Considering Detwinning-induced Plasticity and Transformation-induced Plasticity

Ebrahimi Estahbanati, Parvin | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53288 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Sohrabpour, Saeid; Arghavani Hadi, Jamal; McGarry, Patrick
  7. Abstract:
  8. The main goal of the current study is to incorporate the effect of microstructural deformation mechanisms, such as detwinning-induced plasticity, into constitutive and computational modeling of NiTi shape memory alloys. Therefore, based on thermodynamic considerations a new inelastic mechanism, detwinning-induced plasticity (DIP), is proposed for modelling the response of NiTi SMAs to cyclic loading. DIP is incorporated into a constitutive framework that also includes other well-established inelastic mechanisms of phase transformation, transformation-induced plasticity, residual martensite and detwinning. The model is constructed at the single crystal scale using the framework of thermodynamics and a crystal plasticity formulation. Then, adopting an explicit scale transition rule, it is transformed to polycrystalline version for simulation of published experimental test data. Thermodynamic considerations result in a strong contribution of DIP for cyclic loading regimes where compressive stress occurs during part of the loading cycle. However, the contribution of DIP is negligible for cyclic loading regimes that result exclusively in tensile stress. Inclusion of DIP results in improved prediction of experimentally observed NiTi SMAs behavior. In strain-controlled cyclic compression-unloading tests, DIP leads to a less negative peak stress (6.5% for minimum strain of -2.5%, and 6% for minimum strain of -3.5% in the 50th cycle) and a more negative residual strain (10.4% for minimum strain of -2.5%, and 8.7% for minimum strain of -3.5% in the 50th cycle) following several loading cycles. In stress-controlled tension-compression loading, DIP leads to a reduction of peak strains (7.8% for loading case of , and 17.8% for loading case of in the 160th cycle) and residual strains (12% for loading case of , and 52.7% for loading case of in the 160th cycle) following loading cycles. Mechanical response of NiTi SMAs to cyclic loading in large deformation is investigated as well. The developed model is incorporated into the finite element framework via a VUMAT subroutine in the finite element package Abaqus. A cubic Representative Volume Element (RVE) with different crystals is then considered to reach a mesh-independent result. We then establish the role of texture on the mechanical behavior of NiTi in our modeling framework. The proposed model is capable of capturing different features observed in the experimental results
  9. Keywords:
  10. Constitutive Modeling ; Large Deformation ; Transformation Induced Plasticity (TRIP)Steel ; Finite Element Method ; Crystal Plasticity ; Nitinol Alloy ; Detwinning-Induced Plasticity

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