Date of Award

2022

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Trisha Sain

Committee Member 1

Gregory Odegard

Committee Member 2

Ibrahim Miskioglu

Committee Member 3

Qingli Dai

Abstract

The ease of processing, recyclability, and ideal cost to weight ratio makes the semi-crystalline polymers attractive in the aerospace, automotive, and defense industries. Use of semicrystalline polymers for engineering design requires a thorough understanding of their response to mechanical deformation, rate of loading, temperature, and failure mechanisms. However, there lacks a generally agreed upon constitutive model to capture the large deformation elastic-viscoplastic response of semicrystalline polymers while incorporating the strain-rate dependence and damage behavior. To address this aspect, the objective of this dissertation is to develop an elastic-viscoplastic constitutive model to predict the rate dependent, large deformation response of semicrystalline polymers under tension and compression. In addition, a continuum scale damage model coupled with viscoplasticity is adopted to incorporate cavitation induced damage growth, coalescence, and fibrillation in the material. To validate the proposed model, uniaxial compression and tension experiments are conducted on isotactic polypropylene homopolymer within strain rates of 10-3 s-1 to 10-1 s-1. The constitutive model is implemented in a finite element program ABAQUS/Explicit (ABAQUS 2017) by writing a user material subroutine (VUMAT). With the model parameters properly calibrated, the present study shows that the proposed constitutive model is able to predict the macroscopic rate dependent load-displacement curves, as well as the fracture responses for various standard geometries.

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