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dc.contributor.advisorSuo, Zhigang
dc.contributor.authorJin, Lihua
dc.date.accessioned2014-10-21T15:36:19Z
dc.date.issued2014-10-21
dc.date.submitted2014
dc.identifier.citationJin, Lihua. 2014. Mechanical Instabilities of Soft Materials: Creases, Wrinkles, Folds, and Ridges. Doctoral dissertation, Harvard University.en_US
dc.identifier.otherhttp://dissertations.umi.com/gsas.harvard.inactive:11846en
dc.identifier.urihttp://nrs.harvard.edu/urn-3:HUL.InstRepos:13064983
dc.description.abstractSubject to a sufficiently large compression, materials may undergo mechanical instabilities of various types. When the material is homogeneous, creases set in. When the material is a bilayer consisting of a stiff thin film on a thick compliant substrate, wrinkles set in. Creases are localized self-contact regions with large strain deviating from the smooth state, while wrinkles are undulations finite in space with infinitesimal strain deviating from the smooth state. After the formation of wrinkles, if the compression further increases, wrinkles double their period and form localized folds. If the substrate is subject to a sufficiently large pre-tension, wrinkles transit to ridges. This thesis explores different types of mechanical instabilities: creases, wrinkles, folds, and ridges. We start with studying creases in different materials. Soft tissues growing under constraint often form creases. We adopt the model of growth that factors the deformation gradient into a growth tensor and an elastic deformation tensor, and show that the critical conditions for the onset of creases take a remarkably simple form. We then perform simulations to explore creases in strain-stiffening materials. For a solid that stiffens steeply at large strains, as the compression increases, the surface is initially smooth, then forms creases, and finally becomes smooth again. For a solid that stiffens steeply at small strains, creases never form for all levels of compression. In order to better control the formation and disappearance of creases, we design a soft elastic bilayer with same moduli of the film and substrate but the substrate pre-compressed, and show that the bilayer can snap between the flat and creased states reproducibly with tunable hysteresis in a large strain range. We also show that an interface between two soft materials can form creases under compression. We then investigate the critical conditions for the onset of wrinkles and creases in bilayers with arbitrary thicknesses and moduli of the two layers, and show several new types of bifurcation behavior when the film and substrate have comparable moduli and thicknesses. We study the effect of substrate pre-stretch on post-wrinkling bifurcations, and show that pre-tension stabilizes wrinkles while pre-compression destabilizes wrinkles. When the pre-compression is sufficiently large, `chaotic' morphologies emerge. When the pre-tension is sufficiently large, we realize ridge localizations and networks under an equi-biaxial compression, and study the mechanics of ridge formation and propagation.en_US
dc.description.sponsorshipEngineering and Applied Sciencesen_US
dc.language.isoen_USen_US
dash.licenseLAA
dc.subjectMechanicsen_US
dc.subjectcreaseen_US
dc.subjectfolden_US
dc.subjectmechanical instabilityen_US
dc.subjectridgeen_US
dc.subjectsoft materialen_US
dc.subjectwrinkleen_US
dc.titleMechanical Instabilities of Soft Materials: Creases, Wrinkles, Folds, and Ridgesen_US
dc.typeThesis or Dissertationen_US
dash.depositing.authorJin, Lihua
dc.date.available2014-10-21T15:36:19Z
thesis.degree.date2014en_US
thesis.degree.disciplineEngineering and Applied Sciencesen_US
thesis.degree.grantorHarvard Universityen_US
thesis.degree.leveldoctoralen_US
thesis.degree.namePh.D.en_US
dc.contributor.committeeMemberRice, Jamesen_US
dc.contributor.committeeMemberMahadevan, Lakshminarayananen_US
dc.contributor.committeeMemberRubinstein, Shmuelen_US
dash.contributor.affiliatedJin, Lihua


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