Theses and Dissertations
Issuing Body
Mississippi State University
Advisor
Horstemeyer, Mark F.
Committee Member
Rhee, Hongjoo
Committee Member
Bouvard, Jean-Luc
Committee Member
Lacy, Thomas E. Jr
Date of Degree
5-11-2013
Document Type
Dissertation - Open Access
Major
Mechanical Engineering
Degree Name
Doctor of Philosophy
College
James Worth Bagley College of Engineering
Department
Department of Mechanical Engineering
Abstract
This dissertation proposes a modi ed internal state variable (ISV) inelastic damage model that was motivated by experimental structure{property relations of thermoplastics. In particular, a new damage model was developed for glassy, amorphous thermoplastics. ISV evolution equations are de ned through thermodynamics, kinematics, and kinetics for isotropic damage arising from two di erent inclusion types: pores and particles. The damage arising from the particles and crazes is accounted for by three processes: damage nucleation, growth, and coalescence. Damage nucleation is de ned as the number density of voids/crazes. The associated ISV rate equation is a function of stress state, molecular weight, fracture toughness, particle size, particle volume fraction, temperature, and strain rate. The damage growth is based upon a single void growing and its growth is de ned by an ISV rate equation that is a function of stress state, strain rate sensitivity, and strain rate. The coalescence ISV equation enables interaction between voids and crazes and is a function of the nearest neighbor distance between voids/crazes, size of voids/crazes, temperature, and strain rate. The damage arising from pre-existing voids employs the Cocks{Ashby void growth rule. The total void volume fraction is a summation of the damage arising from particles, pores, and crazes. Micromechanical modeling results for a single void compare well to experimental ndings garnered from the literature. This formulation is then implemented into a nite element analysis. For damage evolution, comparisons are made between a one-dimensional material point simulator and a three-dimensional nite element (FE) simulation. Finally, good agreement is found between impact experiments and FE impact simulations using the implemented model.
URI
https://hdl.handle.net/11668/18278
Recommended Citation
Francis, David K., "An Empirically Validated Multiscale Continuum Damage Model for Thermoplastic Polymers Subjected to Variable Strain Rates" (2013). Theses and Dissertations. 514.
https://scholarsjunction.msstate.edu/td/514
