Constitutive modeling and optimal design of polymeric foams for crashworthiness.

摘要

This dissertation contains work on polymeric foam phenomenological constitutive modeling, numerical implementation, microscopic deformation analysis and optimal design of polymeric cellular structures. The constitutive models are implemented as material subroutines in the explicit finite element program LS-DYNA3D for vehicle crashworthiness numerical simulation. The polymeric foams include polyurethane (PU) foams, polystyrene (PS) foams, and polypropylene (PP) foams. Results from this work will provide essential knowledge for the analysis and design of prototype motor vehicle impact energy management systems. Comprehensive experiment on these polymeric foams has been conducted by the Material Research Lab of the Department of Civil and Environment Engineering. The experimental results have been reviewed in this dissertation for the material constitutive modeling. The testing modes include: (1) uniaxial compression, (2) simple shear, and (3) hydrostatic compression. Focus has been placed on strain rate and temperature sensitivities. The deformation is applied up to 80% volumetric strain. The strain rate ranges from quasi-static to dynamic. Temperature ranges from {dollar}-{dollar}20{dollar}spcirc{dollar}C to 80{dollar}spcirc{dollar}C. Procedures for numerical implementation are discussed in detail. Numerical examples are presented to validate the material constitutive model. In this research, a self-consistent microstructure-based constitutive modeling technique is also presented. The numerical procedure is based on the homogenization method for periodic composites. The representative volume element modeling is aided by using an image-based fixed-grid finite element method. Numerical examples are presented for linear elastic and nonlinear elasto-plastic problems. Finally, a design optimization method based on homogenization theory for optimal polymeric foam composite structures is introduced. The maximization of structural mean stiffness by redistributing reinforcement material results in a structure with many meso-scale perforations. Polymeric foam may fill these holes to improve the stability of perforated structure. Further, the composition of meso-scale reinforcement and polymeric foam filler provides good static load bearing and hydrodynamic crashworthiness capabilities.