The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Experiments and multi-field modeling of inelastic soft materials
Author:	Wang, Shuolun
View Online:	njit-etd2018-073 (xvi, 104 pages ~ 3.7 MB pdf)
Department:	Department of Mechanical and Industrial Engineering
Degree:	Doctor of Philosophy
Program:	Mechanical Engineering
Document Type:	Dissertation
Advisory Committee:	Chester, Shawn Alexander (Committee chair) Adams, Matthew P. (Committee member) Nadimpalli, Siva P.V. (Committee member) Rao, I. Joga (Committee member) Rosato, Anthony D. (Committee member) Shirokoff, David (Committee member) Singh, Pushpendra (Committee member)
Date:	2018-05
Keywords:	Constitutive modeling Finite element method Inelastic Multi-field Soft materials Solid mechanics
Availability:	Unrestricted
Abstract:	Soft dielectrics are electrically-insulating elastomeric materials, which are capable of large deformation and electrical polarization, and are used as smart transducers for converting between mechanical and electrical energy. While much theoretical and computational modeling effort has gone into describing the ideal, time-independent behavior of these materials, viscoelasticity is a crucial component of the observed mechanical response and hence has a significant effect on electromechanical actuation. This thesis reports on a constitutive theory and numerical modeling capability for dielectric viscoelastomers, able to describe electromechanical coupling, large- deformations, large-stretch chain-locking, and a time-dependent mechanical response. This approach is calibrated to the widely-used soft dielectric VHB 4910, and the finite-element implementation of the model is used to study the role of viscoelasticity in instabilities in soft dielectrics, namely (1) the pull-in instability, (2) electrocreasing, (3) electrocavitation, and (4) wrinkling of a pretensioned three dimensional diaphragm actuator. Results show that viscoelastic effects delay the onset of instability under monotonic electrical loading and can even suppress instabilities under cyclic loading. Furthermore, quantitative agreement is obtained between experimentally measured and numerically simulated instability thresholds. Filled rubber-like materials are important engineering materials, and they are widely used in aerospace, automotive, and other industries. However, their nonlinear, inelastic, and rate-dependent constitutive behavior is not fully understood and modeled with varying degrees of success. Much of the previous literature has focused on either capturing quasi-static stress-softening behavior or rate-dependent viscous effects, but generally not both concurrently. This thesis develops a thermody- namically consistent constitutive model which accounts for both of those phenomena concurrently. A set of comprehensive mechanical tensile tests are conducted on the filled rubber Viton. The constitutive model is then calibrated to the experimental data, and numerically implemented into the finite element package Abaqus by writing a user material subroutine UMAT. The constitutive model is validated by comparing a numerical simulation prediction with an inhomogeneous deformation experiment. As an extension to the study of Viton, this thesis also develops a constitutive model to quantitatively capture thermal recovery of the Mullins effect. The model is then calibrated to experiments in the literature, and numerically implemented by writing a user material subroutine for the finite element program Abaqus/Standard. Lastly, simulation results suggest that the unanticipated behaviors due to recovery of Mullins effect are possible.