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Modeling Stress-strain Behavior of Aluminum Alloy (A356.0) under Thermo-mechanical Loading

Felfeli, Mehran | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44593 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Farrahi, Gholam Hossein
  7. Abstract:
  8. Aluminum alloy (A356.0) is used in the production of cylinder head. Automobile engines are often subjected to thermo-mechanical loadings. In order to investigate the material performance, it is crucial to obtain fatigue properties of the material under thermo-mechanical and isothermal fatigue tests. The specimen is subjected to tensile and compressive stresses in a constant temperature. But in thermo-mechanical tests, the temperature and the strain vary in a specific span (between maximum and minimum values). By using the strain- stress hysteresis loop (obtained by fatigue tests), we can determine fatigue properties. Then, these properties are used in the simulation. In this thesis, constitutive viscoplastic models are used to simulate the strain- stress hysteresis loop and material constants are determined by the genetic algorithm. The objective function for the optimization is the average of absolute of experimental and predicted stress differences. Between selected models, Chaboche's model is able to predict the cyclic behavior of aluminum alloy (A356.0), more properly. Chaboche's model is also compared to other models and the effect of the static recovery and the back stress number are investigated in this model. Modeling of the thermo-mechanical stress is improved obviously by applying the static recovery with three back stresses. Errors in the case of the thermo-mechanical loading (with temperature varying of 50 to 200°C) decrease from 9.5% to 5.0%. In case of isothermal loading, errors of models are less than 9.3%. Errors of models under thermo-mechanical loading in comparison to isothermal loading, increase as also occur in Walker's model. The error in this model, under thermo-mechanical loading with temperature varying of 50 to 200, reaches to 20.8% and for Nagode's model, the error reaches to 20.7%. The minimum error is for Chaboche's model with the static recovery in the isothermal fatigue test at 250°C, which is calculated as 2.0%. In this thesis, models are compared according to the calculation time, required data and other abilities. Besides, advantages and disadvantages of these models are investigated
  9. Keywords:
  10. Aluminum Alloy ; Low Cycle Fatigue ; Thermomechanical Fatigue ; Hardening ; Cyclic Hardening

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