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Permanent link (DOI): https://doi.org/10.7939/R3DX0W

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Deformation and Fracture of Polymers with Work Hardening Behavior Open Access

Descriptions

Other title
Subject/Keyword
HDPE
Cavitation
Strain-rate
Visco-plasticity
Creep
Necking
FEA
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Muhammad, Souvenir
Supervisor and department
Jar, P. -Y. Ben (Department of Mechanical Engineering)
Examining committee member and department
Jar, P. -Y. Ben (Department of Mechanical Engineering)
Moussa, Walied (Department of Mechanical Engineering)
Adeeb, Samer (Department of Civil and Environmental Engineering)
Chen, Weixing (Department of Chemical and Materials Engineering)
Xiao, Xinran (Department of Mechanical Engineering, Michigan State University)
Dennison, Christopher (Department of Mechanical Engineering)
Ayranci, Cagri (Department of Mechanical Engineering)
Department
Department of Mechanical Engineering
Specialization

Date accepted
2014-09-04T15:55:32Z
Graduation date
2014-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Ductile and brittle failure behaviors of semi-crystalline polymers such as high density polyethylene (HDPE) were investigated under uni-axial tensile loading at various test conditions. The first part of the thesis examines the influence of aspect ratio of rectangular cross-section on the tri-axial stress state developed by necking in tensile specimens of HDPE. The approach included both experimental and numerical simulation, and identified that anisotropy is involved in the deformation process during necking. The study shows that with increasing aspect ratio anisotropy in the deformation process increases. A new phenomenological model is then developed in an endeavor to reproduce the experimental work to identify the tri-axial stress state during the large deformation. The innovation lies in the unique technique used to develop the simulation model. The study clearly shows the advantages of this model over previously developed models by other researchers in this field. The results show that the technique is capable of considering non-linear and creep deformation during the necking and has the potential to mimic accurately the stress-strain relationship along with lateral dimensional deformation obtained from the experimental testing. Deformation of HDPE in tension was also analyzed at various crosshead speeds, to quantify the corresponding strain rate and strain rate variation during the necking process. The study clearly states with evidence that the common practice to evaluate the strain rate effect based on the measured total strain is acceptable in spite of the involvement of the creep strain. Another new test methodology developed by using cylindrical specimens with a gauge section design to generate and evaluate bulk cavitation in HDPE. This design is unique, as it has the potential of generating bulk cavitation without the presence of any sharp notch, whereas all the works in literature to study bulk cavitation in polymers involve sharp notch and crack growth. Since no sharp notch is used in the new specimen design, its deformation does not involve crack growth, and therefore, is purely governed by the cavitation-induced rupture process. The FEM results indicate that hydrostatic stress level for bulk cavitation is about three times of that for necking at the same strain level. As a result, the new specimen design has bulk cavitation replace necking as the dominant deformation mechanism in HDPE. The thesis shows that by changing the gauge section geometry, deformation of HDPE specimen under tension can be dominated by either bulk cavitation or the commonly observed necking. The FE results also suggest that the hydrostatic stress at the peak load needs to reach a level similar to the uniaxial yield strength in order to replace the necking by the bulk cavitation.
Language
English
DOI
doi:10.7939/R3DX0W
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
S. Muhammad, and P.-Y. B. Jar, 2010. “Effect of Aspect Ratio on Large Deformation and Necking of Polyethylene,” J. Mater. Sci., 46 (4) 1110-1123.S. Muhammad, and P.-Y. B. Jar, 2013. “Determining Stress-Strain Relationship for Necking in Polymers Based on Macro Deformation Behavior,” Finite Elements in Analysis and Design, 70-71, 36-43.S. Muhammad, and P.-Y. B. Jar, 2014. “Finite Element Modeling to Determine the Strain Rate Variation for Non-Viscous Deformation of HDPE During the Necking Process,” The IUP Journal of Mechanical Engineering, 7 (2) 7-27.P.-Y. B. Jar, Souvenir Muhammad, 2012. “Cavitation-Induced Rupture in High-Density Polyethylene Copolymers,” Polym. Eng. Sci., 52, 1005-1014.

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