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Incremental Modeling of Magnetic Shape Memory Alloys

Khajehsaeid, Hesam | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39904 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Sohrabpour, Saeed
  7. Abstract:
  8. Magnetic Shape Memory Alloys (MSMAs) are a category of active materials which can be excited by magnetic field. These alloys have been used in sensor and actuator applications recently. MSMAs posses special properties such as large magnetic field-induced strains (up to %10) and high actuation frequency (about 1kHz), while ordinary Shape Memory Alloys can’t act in frequencies above 5Hz due to the time involved with heat transformation. In this thesis, MSMAs are modeled by means of incremental modelling which is a useful method in analysis of nonlinear behaviour of materials. Furthermore, stress-strain curve of MSMA is approximated using an analytical expression whose parameters can simply be determined from experimental stress-strain curves. The incremental model is used in predicting magnetic-field-induced strain either under the influence of mechanical stress or in the absence of stress. Also calculation of the magnetic field equivalent stress is modified to predict the superelastic behaviour of MSMA under constant field as well as variable stress. Results obtained from the incremental model are compared with experimental and other theoretical results available in the literature. This comparison exhibits that, error of the incremental model in predicting the maximum field-induced strain is less than 10%, which is lesser than the error of single and three-segment models. Furthermore, another model based on estimation of twinning start and finish stresses, is represented for modelling of superelastic behaviour of MSMA. These stresses are estimated by means of linear and quadratic functions, and the results are used in stress-strain equation. Comparison of the results reveals that, quadratic functions give a better agreement between the model and experimental observations.
  9. Keywords:
  10. Superelasticity ; Incremental Model ; Magnetic-Field-Induced Strain ; Magnetic Shape Memory Alloys (MSMA)

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