Joint Mechanical Engineering (MNE) & Engineering Applied Science (EAS) Seminar by Dr. Ying Li
When: Friday,
April 6, 2018
2:00 PM
-
3:00 PM
Where: Textiles Building 101E
Description: Joint Mechanical Engineering (MNE) and Engineering and Applied Sciences (EAS) SEMINAR
DATE:
April 6, 2018
TIME:
2:00 p.m.-3:00 p.m.
LOCATION:
Textile Building, Room 101E
SPEAKER:
Dr. Ying Li, Assistant Professor Department of Mechanical Engineering,
University of Connecticut
TOPIC:
Multiscale Constitutive Modeling on Finite Strain Viscoelasticity of Elastomers
ABSTRACT:
Elastomers consist of long polymer chains joined together by chemical bonds through cross-linkers. They are usually capable of recovering their original shapes after finite deformation due to covalent cross-linkages. Under equilibrium conditions, long polymer chains making up an elastomer are irregularly coiled together. However, when the elastomer is under tension, polymer chains tend to stretch out and straighten along the pulling direction. Upon unloading, the chains return to their original compact and random arrangement. During such a loading-unloading process, energy dissipates due to friction between polymer chains and the elastomer exhibits viscoelastic behavior. To better understand the viscoelastic behaviors of elastomers, they have been decomposed into a cross-linked network with superimposed free chains. Mathematically, the viscoelasticity of elastomers has been decomposed into hyperelastic and viscous parts, which are attributed to the nonlinear deformation of the cross-linked polymer network and the diffusion of free chains, respectively. The hyperelastic deformation of a cross-linked polymer network is governed by the cross-linking density, the molecular weight of the polymer strands between cross-linkages, and the amount of entanglements between different chains, which we observe through large scale molecular dynamics (MD) simulations. Moreover, a recently developed non-affine network model is confirmed to be able to capture these key physical mechanisms using MD simulation. The energy dissipation during a loading and unloading process of elastomers is governed by the diffusion of free chains, which can be understood through their reptation dynamics. The viscous stress can be formulated using the classical tube model; however, it cannot be used to capture the energy dissipation during finite deformation. By considering the tube deformation during this process, as observed from the MD simulations, we propose a modified tube model to account for the finite deformation behavior of free chains. Combing the non-affine network model for hyperelasticity and modified tube model for viscosity, both understood by molecular simulations, we develop a mechanism-based constitutive model for finite strain viscoelasticity of elastomers. All the parameters in the proposed constitutive model have physical meanings, which are signatures of polymer chemistry, physics or dynamics. More importantly, the finite strain viscoelasticity obtained from our simulations agrees qualitatively with experimental data on both un-vulcanized and vulcanized rubbers, which captures the effects of cross-linking density, the molecular weight of the polymer chain and the strain rate.
BIO:
Dr. Ying Li joined the University of Connecticut in 2015 as an Assistant Professor in the Department of Mechanical Engineering. He received his Ph.D. in 2015 from Northwestern University, focusing on the multiscale modeling of soft matter and related biomedical applications. His current research interests are: multiscale modeling, computational material design, mechanics and physics of soft matter, design of mechanical metamaterials and targeted drug delivery. Dr. Li’s achievements in research have been widely recognized by fellowships and awards including Best Paper award from ASME Global Congress on NanoEngineering for Medicine and Biology (2015), International Institute for Nanotechnology Outstanding Researcher Award (2014), Chinese Government Award for Outstanding Students Abroad (2012) and Ryan Fellowship (2011). He has authored and co-authored more than 60 peer-reviewed articles, including Physical Review Letters, Biomaterials, Nanoscale, Macromolecules, Soft Matter, Polymer, Journal of Mechanics and Physics of Solids etc. He has been invited as reviewer for more than 40 international journals, such as Nature Communications, ACS Nano, Advanced Functional Materials, Carbon, Macromolecules, Journal of Physical Chemistry, ACS Applied Materials & Interfaces, Nanoscale, Chemical Communications and Nanomedicine.
For more information please contact Dr. Jun Li, MNE Seminar Coordinator (jun.li@umassd.edu, 508-999-8692).
All are welcome and light refreshments will be served.
Students taking MNE-500 are REQUIRED to attend! All other MNE and EAS students are encouraged to attend!
Thank you,
Sue Cunha, Administrative Assistant
Mechanical Engineering Department
scunha@umassd.edu
508-999-8492
DATE:
April 6, 2018
TIME:
2:00 p.m.-3:00 p.m.
LOCATION:
Textile Building, Room 101E
SPEAKER:
Dr. Ying Li, Assistant Professor Department of Mechanical Engineering,
University of Connecticut
TOPIC:
Multiscale Constitutive Modeling on Finite Strain Viscoelasticity of Elastomers
ABSTRACT:
Elastomers consist of long polymer chains joined together by chemical bonds through cross-linkers. They are usually capable of recovering their original shapes after finite deformation due to covalent cross-linkages. Under equilibrium conditions, long polymer chains making up an elastomer are irregularly coiled together. However, when the elastomer is under tension, polymer chains tend to stretch out and straighten along the pulling direction. Upon unloading, the chains return to their original compact and random arrangement. During such a loading-unloading process, energy dissipates due to friction between polymer chains and the elastomer exhibits viscoelastic behavior. To better understand the viscoelastic behaviors of elastomers, they have been decomposed into a cross-linked network with superimposed free chains. Mathematically, the viscoelasticity of elastomers has been decomposed into hyperelastic and viscous parts, which are attributed to the nonlinear deformation of the cross-linked polymer network and the diffusion of free chains, respectively. The hyperelastic deformation of a cross-linked polymer network is governed by the cross-linking density, the molecular weight of the polymer strands between cross-linkages, and the amount of entanglements between different chains, which we observe through large scale molecular dynamics (MD) simulations. Moreover, a recently developed non-affine network model is confirmed to be able to capture these key physical mechanisms using MD simulation. The energy dissipation during a loading and unloading process of elastomers is governed by the diffusion of free chains, which can be understood through their reptation dynamics. The viscous stress can be formulated using the classical tube model; however, it cannot be used to capture the energy dissipation during finite deformation. By considering the tube deformation during this process, as observed from the MD simulations, we propose a modified tube model to account for the finite deformation behavior of free chains. Combing the non-affine network model for hyperelasticity and modified tube model for viscosity, both understood by molecular simulations, we develop a mechanism-based constitutive model for finite strain viscoelasticity of elastomers. All the parameters in the proposed constitutive model have physical meanings, which are signatures of polymer chemistry, physics or dynamics. More importantly, the finite strain viscoelasticity obtained from our simulations agrees qualitatively with experimental data on both un-vulcanized and vulcanized rubbers, which captures the effects of cross-linking density, the molecular weight of the polymer chain and the strain rate.
BIO:
Dr. Ying Li joined the University of Connecticut in 2015 as an Assistant Professor in the Department of Mechanical Engineering. He received his Ph.D. in 2015 from Northwestern University, focusing on the multiscale modeling of soft matter and related biomedical applications. His current research interests are: multiscale modeling, computational material design, mechanics and physics of soft matter, design of mechanical metamaterials and targeted drug delivery. Dr. Li’s achievements in research have been widely recognized by fellowships and awards including Best Paper award from ASME Global Congress on NanoEngineering for Medicine and Biology (2015), International Institute for Nanotechnology Outstanding Researcher Award (2014), Chinese Government Award for Outstanding Students Abroad (2012) and Ryan Fellowship (2011). He has authored and co-authored more than 60 peer-reviewed articles, including Physical Review Letters, Biomaterials, Nanoscale, Macromolecules, Soft Matter, Polymer, Journal of Mechanics and Physics of Solids etc. He has been invited as reviewer for more than 40 international journals, such as Nature Communications, ACS Nano, Advanced Functional Materials, Carbon, Macromolecules, Journal of Physical Chemistry, ACS Applied Materials & Interfaces, Nanoscale, Chemical Communications and Nanomedicine.
For more information please contact Dr. Jun Li, MNE Seminar Coordinator (jun.li@umassd.edu, 508-999-8692).
All are welcome and light refreshments will be served.
Students taking MNE-500 are REQUIRED to attend! All other MNE and EAS students are encouraged to attend!
Thank you,
Sue Cunha, Administrative Assistant
Mechanical Engineering Department
scunha@umassd.edu
508-999-8492
Topical Areas: Faculty, General Public, Students, University Community, College of Engineering, Mechanical Engineering, Physics, Lectures and Seminars