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Title:A unified computational framework for process modeling and performance modeling of multi-constituent materials
Author(s):Gajendran, Harishanker
Director of Research:Masud, Arif
Doctoral Committee Chair(s):Masud, Arif
Doctoral Committee Member(s):Duarte, Armando; Elbanna, Ahmed; Uddin, Rizwan
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Variational multiscale method
Mixture theory
Process modeling
Performance modeling
Composites
Abstract:This thesis presents new theoretical and computational developments and an integrated approach for interface and interphase mechanics in the process and performance modeling of fibrous composite materials. A new class of stabilized finite element methods is developed for the coupled-field problems that arise due to curing and chemical reactions at the bi-material interfaces at the time of the manufacturing of the fiber-matrix systems. An accurate modeling of the degree of curing, because of its effects on the evolving properties of the interphase material, is critical to determining the coupled chemo-mechanical interphase stresses that influence the structural integrity of the composite and its fatigue life. A thermodynamically consistent theory of mixtures for multi-constituent materials is adopted to model curing and interphase evolution during the processing of the composites. The mixture theory model combines the composite constituent behaviors in an effective medium, thereby reducing the computational cost of modeling chemically reacting multi-constituent mixtures, while retaining information involving the kinematic and kinetic responses of the individual constituents. The effective medium and individual constituent behaviors are each constrained to mutually satisfy the balance principles of mechanics. Even though each constituent is governed by its own balance laws and constitutive equations, interactive forces between constituents that emanate from maximization of entropy production inequality provide the coupling between constituent specific balance laws and constitutive models. The mixture model is cast in a finite strain finite element framework that finds roots in the Variational Multiscale (VMS) method. The deformation of multi-constituent mixtures at the Neumann boundaries requires imposing constraint conditions such that the constituents deform in a self-consistent fashion. A set of boundary conditions is presented that accounts for the non-zero applied tractions, and a variationally consistent method is developed to enforce inter constituent constraints at Neumann boundaries in the finite deformation context. The new method finds roots in a local multiscale decomposition of the deformation map at the Neumann boundary. Locally satisfying the Lagrange multiplier field and subsequent modeling of the fine scales via edge bubble functions results in closed-form expressions for a generalized penalty tensor and a weighted numerical flux that are free from tunable parameters. The key novelty is that the consistently derived constituent coupling parameters evolve with material and geometric nonlinearity, thereby resulting in optimal enforcement of inter-constituent constraints. A class of coupled field problems for process modeling and for performance molding of fibrous composites is presented that provides insight into the theoretical models and multiscale stabilized formulations for computational modeling of multi-constituent materials.
Issue Date:2016-09-06
Type:Thesis
URI:http://hdl.handle.net/2142/95274
Rights Information:Copyright 2016 Harishanker Gajendran
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12


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