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Multiscale Modeling of Crack Propagation under Thermal Fatigue in Nano-Structured Materials

Yasbolaghi, Reza | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54360 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khoei, Amir Reza
  7. Abstract:
  8. In this research, various molecular dynamics simulations have been carried out and sensitivity of the crack propagation process to the simulation parameters including the load pattern, maximum applied strain, temperature, loading frequency, and percentage of defects is investigated. Moreover, the crack propagation in poly-crystalline structure is studied using a larger model consisting of several atomic crystals and the effect of the presence of crystals on crack growth is investigated. In the next step, a novel coupling technique is developed in the continuum–atomistic multi-scale analysis of temperature field problems. In this manner, a new thermostat is introduced based on the single-atom sub-system, where its capability to control the temperature and produce the canonical ensemble is verified by comparing the distribution of velocities to the Maxwell-Boltzmann distribution. The single-atom sub-system thermostat is then incorporated into the concurrent multi-scale model to relate the temperature field between the continuum and atomistic domains with complex lattice thermal fields. In order to illustrate the capability of the proposed coupling continuum–atomistic model, the multi-scale analysis is performed through several numerical examples at various temperature fields and the results are compared with those obtained from the full atomistic model and finite element simulation. In the next step, the continuum–atomistic multi-scale technique is applied in numerical simulation of the lattice heat conduction in two-dimensional phononic nanostructures. A test setup was constructed from phononic crystals with staggered and aligned lattices of holes and the temperature decay parameter was evaluated after application of a thermal shock at the center of the plate. The results from multi-scale simulations were in agreement with those experimental results. Finally, a method for thermomechanical coupling is presented combining the proposed thermal multi-scale method and the Bridging Domain method. The ability of the proposed method then was evaluated by carrying out different thermomechanical simulations
  9. Keywords:
  10. Molecular Dynamics ; Heat Conduction ; Crack Propagation ; Multiscale Method ; Multi-Scale Hybrid Simulation ; Nanostructure

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