Electronic Theses and Dissertations

Date

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Committee Chair

Ali Fatemi

Committee Member

Joel Bumgardner

Committee Member

Amir Hadadzadeh

Committee Member

Gladius Lewis

Abstract

High-Density Polyethyelen (HDPE) is a very high volume polymer used in many applications such as piping systems in geo-exchange systems or replacing heavier materials in automotive fuel tanks. The most common processing techniques to manufacture HDPE parts are injection molding, blow molding, and compression molding. Combination of cyclic and static loads are inevitable in many applications, therefore, this study investigated tensile, creep, fatigue, and creep-fatigue interaction of HDPE under a variety of conditions including environmental (temperature), stress concentration, cycling frequency, and stress state. Multiaxial stress state effect on fatigue life at room temperature was investigated for HDPE, Polypropylene, neat Nylon 66, and Nylon66 short fiber (%30 glass fiber) composite. The damage mechanisms in the considered thermoplastics were evaluated through experimental fatigue tests. Notch effect on fatigue life was also studied due to the importance of stress concentration effect on fatigue behavior and the fact that they are inevitable in many design situations. Current common multiaxial fatigue criteria were assessed for experimental data and a critical plane-based damage parameter was proposed for multiaxial behavior of HDPE as well as the other studied thermoplastics. Injection molding as a common processing technique for polymers has a high production rate, low manufacturing cost, and flexibility to manufacture complex geometries. Experimental multiaxial fatigue data from literature for injection molded short glass fiber reinforced thermoplastics including Polypropylene, Polybutylene Terephthalate, and Nylon 66 were also included in this study to investigate the effect of fiber orientation on multiaxial fatigue behavior of these polymeric composites with aligned fibers. A modification of the critical plane damage parameter was proposed to account for fiber orientation, mean stress, and stress concentration on multiaxial fatigue behavior of short glass fiber reinforced thermoplastics with injection molding processing technique

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest

Notes

embargoed

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