CHARACTERIZATION, MODELING, AND CONSEQUENCES OF THE DEVELOPMENT DURING PLASTIC FLOW OF LARGE ANISOTROPY IN THE WAVE-SPEEDS

Authors

Quentin Fichot, University of Nebraska – LincolnFollow

Date of this Version

8-2010

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska in Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Engineering Mechanics, Under the Supervision of Professor Mehrdad Negahban. Lincoln, Nebraska: July, 2010
Copyright 2010 Quentin Fichot

Abstract

There is a substantial change in the anisotropy of some glassy polymers when they are subjected to large plastic deformations. The most pronounced case probably is seen in polycarbonate (PC), which is a tough thermoplastic used for many structural applications, including as a protective transparent armor for such applications as bulletproof glass. This development of anisotropy in the elastic response can be of the same order as the applied strains, and, therefore, becomes important in problems that show substantial plastic flow. In spite of this, this characteristic of glassy polymers has not been included in the current models. We propose a change to one of the most common models used for characterizing the mechanical behavior of glassy polymers that has been developed by Boyce et al. and show that this modification captures the observed change in elastic response. We further look at the response of the original Boyce model and the modified model and show that the new model captures all the experimental results to approximately the same accuracy as the original model did. The modified model uses all the same components as the original model, but with a change of the elastic stress-strain response with one constructed to fit the observed development of elastic anisotropy as a result of plastic flow.

We subsequently have implemented this model in ABAQUS VUMAT and have shown that although the modified model captures the quasi-static experimental results with the same accuracy, in wave propagation problems at large plastic flow the two models show substantial differences in wave propagation. Some simulations that reflect this difference are discussed.