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dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorPicu, Catalin R.
dc.contributorShephard, M. S. (Mark S.)
dc.contributorManiatty, Antoinette M.
dc.contributorUnderhill, Patrick T.
dc.contributor.authorShahsavari, Ali
dc.date.accessioned2021-11-03T08:20:31Z
dc.date.available2021-11-03T08:20:31Z
dc.date.created2015-04-23T16:26:27Z
dc.date.issued2013-12
dc.identifier.urihttps://hdl.handle.net/20.500.13015/1368
dc.descriptionDecember 2013
dc.descriptionSchool of Engineering
dc.description.abstractRandom fiber networks are usually modeled by representing each fiber as a Timoshenko or an Euler-Bernoulli beam and each cross-link as either a welded or rotating joint. In this dissertation, the effect of these modeling options on the dependence of the overall linear network modulus on microstructural parameters is studied. It is concluded that Timoshenko beams can be used for the whole range of density and fiber stiffness parameters, while the Euler-Bernoulli model can be used only at relatively low densities. In the low density-low bending stiffness range, elastic strain energy is stored in the bending mode of the deformation, while in the other extreme range of parameters, the energy is stored predominantly in the axial and shear deformation modes. It is shown that both rotating and welded joint models give the same rules for scaling of the network modulus with different micromechanical parameters.
dc.description.abstractThe results presented in this thesis are relevant for many biological and engineering fibrous materials, including connective tissue, the cellular cytoskeleton, special clothing, consumer products, filters, and dampers. It is shown that the overall behavior of the material is very sensitive to several system parameters (power law relationships with large exponents are identified). This allows controlling the system behavior by operating minute changes to these critical parameters. It also creates a knowledge base for the understanding of the mechanics of some biological fiber networks which may be designed to take advantage of these large sensitivities. The identification and description of these effects are the central advance made in this work.
dc.description.abstractThe elastic response of composite random fiber networks in which two types of fibers are used, is studied. This analysis is performed by adding stiff fibers to a relatively softer base while considering two cases: cross-linked and non-cross-linked added fibers. The linear elastic modulus of the network is determined in terms of the system parameters, including the density of added fibers. The results are compared to the case of adding stiff fibers to a homogeneous continuum base. It is shown that there is a threshold of added fiber density, above which the axial stiffens of the base filaments controls the mechanics. In this regime, the elastic response of the composites that have network bases mimics the behavior of those with continuum bases.
dc.description.abstractRandom fiber networks in which fibers are bonded to each other are systems with large multiscale heterogeneity, which controls their mechanical behavior. This pronounced heterogeneity leads to a pronounced size and boundary condition effects on their mechanical behavior. To emphasize the source of the size effect, the network heterogeneity is characterized by analyzing the geometry of the network (density distribution), the strain field and the strain energy distribution. It is shown that the heterogeneity of the mechanical fields depends not only on the network topology, but also on the ratio between the bending and axial stiffness of fibers. In this study, the size effect is quantified and the minimum model size needed to eliminate the size effect for a given set of system parameters, is determined. The results are also used for the selection of the size of representative volume elements useful for multiscale models of fiber networks such as the sequential approach.
dc.description.abstractThe elastic modulus of sparsely cross-linked random fiber networks, i.e. networks in which the degree of cross-linking varies, is studied. The relationship between the micromechanical parameters - fiber density, fiber axial and bending stiffness, and degree of cross-linking - and the overall elastic modulus is presented in terms of a master curve. It is shown that the master plot with various degrees of cross-linking can be collapsed to a curve which is also valid for fully cross-linked networks.
dc.description.abstractRandom fiber networks are present in many biological and non-biological materials such as paper, cytoskeleton, and tissue scaffolds. Mechanical behavior of networks is controlled by the mechanical properties of the constituent fibers and the architecture of the network. To characterize these two main factors, different parameters such as fiber density, fiber length, average segment length, nature of the cross-links at the fiber intersections, ratio of bending to axial behavior of fibers have been considered.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectMechanical engineering
dc.titleMechanical behavior of homogeneous and composite random fiber networks
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid175090
dc.digitool.pid175093
dc.digitool.pid175095
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreePhD
dc.relation.departmentDept. of Mechanical, Aerospace, and Nuclear Engineering


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