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Sintering of Metal Matrix Nanocomposites Under Shock Wave by Coarse Grained Molecular Dynamics

Tavakol, Mahdi | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46366 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Mahnama, Maryam
  7. Abstract:
  8. Nowadays, metal matrix composites due to their magnificent properties, has met diverse applications in automobile, aerospace and military industries. Decreasing the reinforcement size from micro-meter to nano-meter, properties of these structures will be improved significantly. Better properties will lead to better applications for them in the future. Thus, the main objective of the current project was investigation on the mechanical properties of metal matrix nanocomposites produced with shock wave sintering. In order to gain this aim, first the sintering of nanoparticles was modeled. A new model was proposed to consider the neighboring particles effects. Using the model, sintering of many particles can be studied with considering only two particles. Main mechanisms of nanoparticle sintering identified and the effect of powder size and temperature on the governing mechanism was explored. In this way, the conflict between different researches about main mechanism of the nano-sintering eliminated. The sintering activation energy was studied and a reason for the unusual trend of the energy was suggested. In the second section, being benefitted from the first section findings, shock wave sintering modeled with two different methods; NEMD and NPHug. Proper force-field in the range of pressure and temperature under study, identified. Hugoniot curves of the mixture of aluminum and silicon carbide powders, were found. Exploring these curves, it is concluded that an increase in shock pressure helps improve the strength of the final products. For instance, an increase in the shock pressure from 1 GPa to 10 GPa will lead to 50% increase in the ultimate tensile strength. Initial hydrostatic pressure, moreover, deteriorates the strength. For example, in the piston velocity of 0.63 km/s, increasing the initial pressure from 0 to 100 MPa, ultimate tensile strength decreases more than 80%. In the final section, a new model for coarse graining the shock sintering was suggested. Using the model, in contrary to significant decrease in the solution time, no new error will be introduced. Thus, in the current research different stages and mechanisms of nano-sintering, Hugoniot curves of the mixture of aluminum and silicon carbide powders, mechanical properties of shock wave sintering products and coarse grain modeling the shock sintering were explored
  9. Keywords:
  10. Sintering ; Shock Wave ; Molecular Dynamics ; Metal Matrix Nanocomposite ; Metal Matrix Composite (MMC)

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