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Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene

Deformation instabilities, such as microbuckling or lamellar fragmentation due to slip localization, play a very important role in the deformation of semicrystalline polymers, although it still not well explored. Such instabilities often appear necessary to modify the deformation path and facilitate...

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Autores principales: Bartczak, Zbigniew, Vozniak, Alina
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7599652/
https://www.ncbi.nlm.nih.gov/pubmed/32993078
http://dx.doi.org/10.3390/polym12102208
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author Bartczak, Zbigniew
Vozniak, Alina
author_facet Bartczak, Zbigniew
Vozniak, Alina
author_sort Bartczak, Zbigniew
collection PubMed
description Deformation instabilities, such as microbuckling or lamellar fragmentation due to slip localization, play a very important role in the deformation of semicrystalline polymers, although it still not well explored. Such instabilities often appear necessary to modify the deformation path and facilitate strain accommodation in an energy-minimizing manner. In this work, microbuckling instability was investigated using partially oriented, injection-molded (IM) samples of high-density polyethylene, deformed by a plane-strain compression. Deformed samples were probed by SEM, X-ray (small- and wide-angle X-ray scattering: SAXS, WAXS), and differential scanning calorimetry (DSC). It was found that microbuckling instability, followed quickly by the formation of lamellar kinks, occurred in high-density polyethylene (HDPE) at a true strain of about e = 0.3–0.4, mainly in those lamellar stacks which were initially oriented parallel to the compression direction. This phenomenon was observed with scanning electron microscopy, especially in the oriented skin layers of IM specimens, where a chevron morphology resulting from lamellae microbuckling/kinking was evidenced. Macroscopically, this instability manifested as the so-called “second macroscopic yield” in the form of a hump in the true stress–true strain curve. Microbuckling instability can have a profound effect on the subsequent stages of the deformation process, as well as the resulting structure. This is particularly important in deforming well-oriented lamellar structures—e.g., in drawing pre-oriented films of a semicrystalline polymer, a process commonly used in many technologies.
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spelling pubmed-75996522020-11-01 Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene Bartczak, Zbigniew Vozniak, Alina Polymers (Basel) Article Deformation instabilities, such as microbuckling or lamellar fragmentation due to slip localization, play a very important role in the deformation of semicrystalline polymers, although it still not well explored. Such instabilities often appear necessary to modify the deformation path and facilitate strain accommodation in an energy-minimizing manner. In this work, microbuckling instability was investigated using partially oriented, injection-molded (IM) samples of high-density polyethylene, deformed by a plane-strain compression. Deformed samples were probed by SEM, X-ray (small- and wide-angle X-ray scattering: SAXS, WAXS), and differential scanning calorimetry (DSC). It was found that microbuckling instability, followed quickly by the formation of lamellar kinks, occurred in high-density polyethylene (HDPE) at a true strain of about e = 0.3–0.4, mainly in those lamellar stacks which were initially oriented parallel to the compression direction. This phenomenon was observed with scanning electron microscopy, especially in the oriented skin layers of IM specimens, where a chevron morphology resulting from lamellae microbuckling/kinking was evidenced. Macroscopically, this instability manifested as the so-called “second macroscopic yield” in the form of a hump in the true stress–true strain curve. Microbuckling instability can have a profound effect on the subsequent stages of the deformation process, as well as the resulting structure. This is particularly important in deforming well-oriented lamellar structures—e.g., in drawing pre-oriented films of a semicrystalline polymer, a process commonly used in many technologies. MDPI 2020-09-26 /pmc/articles/PMC7599652/ /pubmed/32993078 http://dx.doi.org/10.3390/polym12102208 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Bartczak, Zbigniew
Vozniak, Alina
Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene
title Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene
title_full Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene
title_fullStr Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene
title_full_unstemmed Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene
title_short Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene
title_sort microbuckling instability and the second yield during the deformation of semicrystalline polyethylene
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7599652/
https://www.ncbi.nlm.nih.gov/pubmed/32993078
http://dx.doi.org/10.3390/polym12102208
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