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Rate effects on localized shear deformation during nanosectioning of an amorphous thermoplastic polymer
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
(Tillämpad materialvetenskap, Applied Materials Sciences)
(Tillämpad mekanik, Applied Mechanics)
(English)In: Article in journal (Other academic) Submitted
Abstract [en]

To investigate the effects of loading rate on the thermomechanical behavior of thermoplastic polymer, polymethyl methacrylate (PMMA) sections with a thickness below 100 nm were made at different sectioning speeds by an instrumented ultramicrotome and the sectioning forces were measured. Atomic force microscopy was used to characterize the topographical features of the sectioned surfaces. Periodic structures of shear localizations were observed to form when the sectioning speed exceeded a critical value. With the measured sectioning parameters and other parameters determined based on previous studies, the effects of sectioning speed on the thermomechanical response of this polymer were analyzed using an existing adiabatic shearing model and a suitable constitutive law. A sectioning speed for the onset of shear localization was predicted, agreeing with the experimental results. The method presented in this work provides an approach to analyze the formation of shear localizations in polymers at the nanometer scale deformation. 

National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:uu:diva-328887OAI: oai:DiVA.org:uu-328887DiVA: diva2:1138158
Available from: 2017-09-04 Created: 2017-09-04 Last updated: 2017-09-04
In thesis
1. Mechanical Properties and Deformation Behaviour of Polymer Materials during Nanosectioning: Characterisation and Modelling
Open this publication in new window or tab >>Mechanical Properties and Deformation Behaviour of Polymer Materials during Nanosectioning: Characterisation and Modelling
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Research in local fracture processes and micro-machining of polymers and polymer-based composites has attracted increasing attention, in development of composite materials and miniaturisation of polymer components. In this thesis, sectioning (machining) of a glassy polymer and a carbon nanotube based composite at the nanoscale was performed by an instrumented ultramicrotome. The yield stresses and fracture toughness of these materials were determined by analysing the sectioning forces. Fractographic analysis by atomic force microscopy was conducted to characterise the topographies and elastic properties of the sectioned surfaces to explore the deformation and fracture behaviour of the polymer during nanosectioning. The study reveals that a transition from homogenous to shear localised deformation occurred as the uncut chip thickness (depth of cut) or sectioning speed increased to a critical value. Analytical and finite element methods were used to model the nanosectioning process. The shear localised deformation was caused by thermal softening due to plastic dissipation. Although not considering sectioning, the tensile properties of a polymer nanocomposite were additionally investigated, where the degree of nanofibrillation and polyethylene glycol (PEG) content had significant effects.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 49 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1553
Keyword
Nanosectioning; Fracture toughness; Adiabatic shearing; Shear band; Nanosectioning; Glassy polymer; Nanocomposite
National Category
Applied Mechanics
Identifiers
urn:nbn:se:uu:diva-328906 (URN)978-91-513-0062-7 (ISBN)
Public defence
2017-10-20, Häggsalen Ångströmlaboratoriet, Lägerhyddsvägen 1, 752 37, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-09-21 Created: 2017-09-04 Last updated: 2017-10-18

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CiteExportLink to record
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