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Rate-dependent Buckling and Creasing Mechanics of Elastic and Viscoelastic Films under Compression

Xianheng, Guan (2022) Rate-dependent Buckling and Creasing Mechanics of Elastic and Viscoelastic Films under Compression. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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This thesis examines two situations in the buckling of thin films subjected to compression: the buckling of elastic thin films attached to viscous substrates, and the free-surface creasing of a viscoelastic liquid.
When a thin film on a layer viscous liquid is compressed steadily at a fixed rate, two distinct buckling modes are observed: roughly-sinusoidal, global wrinkling, and formation of highly-localized ridges well-separated by more-or-less flat regions. Although both buckling modes have been reported previously, there is no understanding of ridge localization. Further, the quantitative aspects of how parameters such as loading rate and liquid substrate thickness influence the buckling process are also unknown. With our experiments and simulations, ridge localization can be understood as buckling phenomenon starting with wrinkles emerging in the form of wave packets with a longer length scale modulation which is rate-dependent. The size of these wave packets captures the dependence of inter-ridge on the compression rate and the liquid layer thickness observed far from threshold in experiment and simulation. Further, the effects of end-relaxation on the buckling behavior for relatively short films were also examined by simulations.
It is well-known that the free surface of an elastic material develops sharp cusp-like creases when compressed beyond a certain critical strain. Here we examine a viscoelastic fluid under similar compression. Experiments show that a viscoelastic liquid undergoes a similar, but rate-dependent, creasing instability such that the strain required for creasing increases as rate decreases. A model is developed wherein the creasing criterion known previously for neo-Hookean elastic solids is applied to the elastic portion of the deformation of a viscoelastic liquid. Using the upper-convected Maxwell model for viscoelasticity, we derive an analytical criterion for viscoelastic creasing which is in good agreement with experiments. It predicts that the strain for creasing increases with decreasing Weissenberg number, and creasing is not possible below a critical Weissenberg number.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Xianheng, Guanxig35@pitt.eduxig35
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairSachin,
Committee MemberQihan,
Committee MemberLeu,
Committee MemberSpandan,
Committee MemberPatrick,
Date: 6 September 2022
Date Type: Publication
Defense Date: 9 May 2022
Approval Date: 6 September 2022
Submission Date: 9 June 2022
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 136
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Mechanical Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Buckling,ridge localization,wrinkling,creasing
Date Deposited: 06 Sep 2022 16:01
Last Modified: 06 Sep 2022 16:01


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