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A New Method Based on Crystal Plasticity Finite Element to Predict the Formability of Steel Sheets with Spheroidal Cementites

Einolghozati, Mona | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56451 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Assempour, Ahmad
  7. Abstract:
  8. In this research, using the crystal plasticity finite element method, the effects of various microstructural features on behavior of spherical steel sheets have been investigated. The cementite phase ratio, the grain sizes of ferrite and cementite, and the percentage of residual pearlite in the steel structure due to incomplete annealing are the major microstructural parameters studied in this work. A grain generator software has been developed to generate ferrite grains as well as cementite particles distributed in the ferrite matrix. A hard coating with special properties as an intermediate layer around the cementite grains has been considered to simulate the contact between ferrite grains and cementite particles. This software can also assist with the preprocessing including boundary conditions and loadings and introducing constitutive modeling relations. The representative volume elements (RVEs) are used to simulate the microstructure of the steel sheet. The hardening parameters in the simulations are calibrated according to the available experimental data in the literature. The calibrated model is used to predict the forming limit diagram (FLD) of the steel sheet. The onset of plastic instability was determined using the microstructural inhomogeneity criterion incorporated into the RVE under various loading paths. Then, the predicted FLD was compared with the experimental results obtained in this project. Finally, this method is used to investigate the effects of different microstructural features on the formability of the spheroidized steel sheet. It is shown that with a 10% increase in the cementite phase, the limit strains decrease by about 25% and with reducing the size of ferrite and cementite grains, the strength of steel increases by about 5%. Also, with the increase in the particles fraction in the central band and the decrease in the bandwidth, homogeneous deformation of the steel is also reduced
  9. Keywords:
  10. Crystalline Plasticity ; CK45 Steel ; Forming Limit Diagram (FLD) ; Cementite ; Ductility ; Preprocessing Software ; Cementite Spheroidized Steel

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