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Multiscale modeling of microcrystalline materials

Citation

Hurtado, Daniel E. (2011) Multiscale modeling of microcrystalline materials. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:11222010-061455728

Abstract

Materials with micrometer dimensions and their distinct mechanical properties have generated a great interest in the material science community over the last couple of decades. There is strong experimental evidence showing that microcrystalline materials are capable of achieving much higher yield and fracture strength values than bulk mesoscopic samples as they decrease in size. Several theories have been proposed to explain the size effect found in micromaterials, but a predictive physics-based model suitable for numerical simulations remains an open avenue of research. Since the successful design of micro-electro-mechanical systems (MEMS) and novel engineered materials hinges upon the mechanical properties at the micrometer scale, there is a compelling need for a quantitative and accurate characterization of the size effects exhibited by metallic micromaterials. This work is concerned with the multiscale material modeling and simulation of strength in crystalline materials with micrometer dimensions. The elasto-viscoplastic response is modeled using a continuum crystal plasticity formulation suitable for large-deformation problems. Crystallographic dislocation motion is accounted for by stating the crystal kinematics within the framework of continuously distributed dislocation theory. The consideration of the dislocation self-energy and the step formation energy in the thermodynamic formulation of the constitutive relations renders the model non-local and introduces a length scale. Exploiting the concept of total variation we are able to recover an equivalent model that is local under a staggered approach, and therefore amenable to time integration using variational constitutive updates. Numerical simulations of compression tests in nickel micropillars using the proposed multiscale framework quantitatively capture the size dependence found in experimental results, showcasing the predictive capabilities of the model.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:crystal plasticity, multiscale material modeling, dislocations, strain-gradient plasticity, size effects, micropillar
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Minor Option:Applied And Computational Mathematics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ortiz, Michael
Thesis Committee:
  • Ortiz, Michael (chair)
  • Bhattacharya, Kaushik
  • Ravichandran, Guruswami
  • Greer, Julia R.
Defense Date:27 October 2010
Author Email:dhurtado (AT) caltech.edu
Record Number:CaltechTHESIS:11222010-061455728
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:11222010-061455728
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6187
Collection:CaltechTHESIS
Deposited By: Daniel Hurtado Sepulveda
Deposited On:07 Dec 2010 16:47
Last Modified:26 Dec 2012 04:32

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