Nguyen, Chien M
(2023)
Plasticity-induced bending of aluminum-polymer layered composites.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
Deformation induced strain mismatch refers to the phenomenon where different materials bonded to each other experience different levels of inelastic deformation when subjected to external stress. This difference in deformation induces a strain mismatch, which can then cause permanent deformation of the composite. This thesis examines bilayered composites subjected to tensile stress which induces inelastic deformation in one of the layers. The resulting strain mismatch causes the bilayer system to bend when the stress is released. The resulting bending can have important implications for the mechanical behavior of multilayered thin films as well as for applications such as sensors or actuators. Understanding the factors that influence deformation induced strain mismatch and the resulting bending is therefore critical for the design and optimization of such systems.
Experiments are conducted on layered composites of soft aluminum foil and commercial polymer laminating film. Bilayers were manufactured by cold lamination, then cut into strips, and stretched to induce inelastic deformation. The bilayer strips were then unloaded from various strains and observed to bend. The bending curvature was quantified and found to increase almost linearly with the applied strain. The bending was found to reduce with increasing aluminum thickness, and to be insensitive to sample width. Aluminum-polymer bilayers that used thin foils of aluminum undergo localized delamination which relieve strain mismatch in their vicinity and therefore suppresses bending.
By patterning the bilayers, bending can be localized only at specific “defect” sites. Such defects were created by laser-ablation of the polymer. Simple trenches were made with different angles in respect to the pulling direction, or different width. When stretched and released, such composites show spatially-heterogeneous bending. Complex 3D shapes can be made by combining trenches or cutouts.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
13 June 2023 |
| Date Type: |
Publication |
| Defense Date: |
7 April 2023 |
| Approval Date: |
13 June 2023 |
| Submission Date: |
11 April 2023 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
56 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Mechanical Engineering |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
plasticity, bending, origami, strain mismatch, shape morphing |
| Date Deposited: |
13 Jun 2023 14:08 |
| Last Modified: |
13 Jun 2023 14:08 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/44525 |
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