Abstracts

Biological and synthetic active materials have attracted a large amount of research attention over the last decade. This thesis is focuses on the development of constitutive models and computational frameworks for describing the behavior of active anisotropic materials. Active anisotropic materials are defined as consisting of an isotropic matrix embedded with fibers or oriented particles that are active. In this dissertation, new constitutive formulations for active anisotropic materials undergoing finite deformations are proposed and analyzed within a generalized continuum mechanics framework. The constitutive equations have been developed for two material classes: i) natural biological muscle tissue and ii) synthetic electroactive polymers. The proposed constitutive models are successfully implemented into a finite element environment to study a range of initial boundary value problems. In the first material class, a structure-based continuum model is proposed to capture the viscoelastic behavior due to smooth muscle tissue contractility. We employed a thick-walled model for healthy and diseased arteries to investigate the effect of active viscoelasticity on the mechanical response of the artery wall. The work focuses on the artery being overstretched on long time scales (around 1 minute), for example, during surgical events such as balloon angioplasty and stent implantation. Model results show an over fourfold increase in circumferential stresses and twofold increase in radial stresses when active viscoelasticity is considered. This suggests that active viscoelasticity has a non-negligible effect on the artery wall stresses when longer timescales are considered. In the second material class, a novel dielectric elastomer composite consisting of an isotropic matrix and embedded contractile fibers is proposed. Two activation modes are realized: through thickness actuation of the matrix and fiber actuation in the plane. A constitutive model is proposed to model the active anisotropic material behavior. A new user subroutine was developed for the proposed constitutive model and implemented into the commercial finite element software ABAQUS. A series of computational simulations to highlight novel deformation modes of the proposed dielectric elastomer composite are presented. The proposed composite significantly extends the actuation performance space for dielectric elastomers. Several new spatial architectures are proposed and the simulations demonstrate coordinated surface morphing through spatial activation and as a function of fiber orientation. Finally, we calculate the actuation response for complex 3D geometries, which opens the design space even further. The developed computational framework is demonstrated to be a very convenient and efficient numerical tool to study complex materials.Advisors/Committee Members: Goulbourne, Nakhiah C (committee member), Wineman, Alan S (committee member), Shaw, John A (committee member), Sundararaghavan, Veera (committee member).