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Mechanical behaviour of glassy polymers: experiments and modelling

Engqvist, Jonas LU (2016)
Abstract (Swedish)
This thesis presents experimental investigation and modelling of the mechanical response of glassy polycarbonate (PC) during deformation. The mechanical response is studied experimentally over a wide range of length-scales using X-ray scattering techniques and optical full-field deformation measurement by Digital Image Correlation (DIC). Results from the experimental work have been used to develop an elasto-viscoplastic model for glassy polymers. The thesis includes an introductory section on glassy polymers, aspects of the experimental procedures and a summary of the key aspects of the constitutive modelling, and four papers.

An experimental method combining X-ray scattering, full-field DIC and tensile loading has been developed... (More)
This thesis presents experimental investigation and modelling of the mechanical response of glassy polycarbonate (PC) during deformation. The mechanical response is studied experimentally over a wide range of length-scales using X-ray scattering techniques and optical full-field deformation measurement by Digital Image Correlation (DIC). Results from the experimental work have been used to develop an elasto-viscoplastic model for glassy polymers. The thesis includes an introductory section on glassy polymers, aspects of the experimental procedures and a summary of the key aspects of the constitutive modelling, and four papers.

An experimental method combining X-ray scattering, full-field DIC and tensile loading has been developed and used within this thesis. Details about the experimental method are presented in Paper A. By combining the, individually well established, experimental techniques, the deformation of a material can be studied simultaneously over a wide range of length-scales, from the macroscopic response down to the behaviour of the molecular structure. Results from experiments performed using the developed method are also presented in Paper B. Novel observations of the deformation and reorientation of the microstructure of glassy PC are presented and related to relevant local macroscopic measures of deformation.

The experimental results presented in Paper B have been used to develop a constitutive model for glassy polymers in Paper C. A separate microstructural deformation gradient is introduced to model the deformation of the polymer network. Moreover, the reorientation of the microstructure, shown in Paper B, is introduced by an evolution of the directions of the network chains. By incorporating the evolving reorientation and the deformation of the microstructure shown by the experiments, the model is able to capture the deformation at the macroscopic, the mesoscopic and the microscopic levels.

In Paper D, the mechanical behaviour of glassy PC is studied using biaxial tension loading and DIC. The experiments performed in Paper D show a significant influence of the multi-axial loading on the localisation behaviour. It is also found that the commonly used quadratic form of the elastic free energy results in a too stiff initial response during biaxial loading. To this end, a new format for the volumetric part of the elastic free energy is proposed which results in a softer response with increasing volumetric deformation. The proposed format also improves the ability to capture the non-linear, pre-peak behaviour exhibited by PC.
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author
organization
publishing date
type
Thesis
publication status
published
subject
pages
134 pages
publisher
Division of Solid Mechanics
ISBN
978-91-7623-816-5
language
English
LU publication?
yes
id
e4e6b7d0-d8f4-4e61-bc04-02b493115c61
date added to LUP
2016-05-16 08:52:23
date last changed
2016-05-17 12:38:10
@phdthesis{e4e6b7d0-d8f4-4e61-bc04-02b493115c61,
  abstract     = {This thesis presents experimental investigation and modelling of the mechanical response of glassy polycarbonate (PC) during deformation. The mechanical response is studied experimentally over a wide range of length-scales using X-ray scattering techniques and optical full-field deformation measurement by Digital Image Correlation (DIC). Results from the experimental work have been used to develop an elasto-viscoplastic model for glassy polymers. The thesis includes an introductory section on glassy polymers, aspects of the experimental procedures and a summary of the key aspects of the constitutive modelling, and four papers.<br/><br/>An experimental method combining X-ray scattering, full-field DIC and tensile loading has been developed and used within this thesis. Details about the experimental method are presented in Paper A. By combining the, individually well established, experimental techniques, the deformation of a material can be studied simultaneously over a wide range of length-scales, from the macroscopic response down to the behaviour of the molecular structure. Results from experiments performed using the developed method are also presented in Paper B. Novel observations of the deformation and reorientation of the microstructure of glassy PC are presented and related to relevant local macroscopic measures of deformation.<br/><br/>The experimental results presented in Paper B have been used to develop a constitutive model for glassy polymers in Paper C. A separate microstructural deformation gradient is introduced to model the deformation of the polymer network. Moreover, the reorientation of the microstructure, shown in Paper B, is introduced by an evolution of the directions of the network chains. By incorporating the evolving reorientation and the deformation of the microstructure shown by the experiments, the model is able to capture the deformation at the macroscopic, the mesoscopic and the microscopic levels. <br/><br/>In Paper D, the mechanical behaviour of glassy PC is studied using biaxial tension loading and DIC. The experiments performed in Paper D show a significant influence of the multi-axial loading on the localisation behaviour. It is also found that the commonly used quadratic form of the elastic free energy results in a too stiff initial response during biaxial loading. To this end, a new format for the volumetric part of the elastic free energy is proposed which results in a softer response with increasing volumetric deformation. The proposed format also improves the ability to capture the non-linear, pre-peak behaviour exhibited by PC.<br/>},
  author       = {Engqvist, Jonas},
  isbn         = {978-91-7623-816-5},
  language     = {eng},
  pages        = {134},
  publisher    = {Division of Solid Mechanics},
  school       = {Lund University},
  title        = {Mechanical behaviour of glassy polymers: experiments and modelling},
  year         = {2016},
}