Gopalan Ramachandran, Rahul
(2022)
Large deformation behavior of rubber-plastic laminates.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
We study the large deformation behavior of rubber-plastic laminates in this thesis. Tensile, fracture, and shape programming with uniaxial tensile deformation is discussed. This research showed that the tensile behavior of the laminates resembles a second-order phase transition. For sufficiently small rubber/plastic thickness ratio, the rubber-plastic laminates showed necking and drawing, wherein a tensile bar coexists in two strain states, one with a large stretch (necked phase) and the other with a modest stretch (unnecked phase). With increasing rubber/plastic thickness ratio, the two strain states approached each other, culminating in a critical point. The distinct effect of rubber properties, i.e., modulus and strain hardening, on the phase diagram and the critical point are also discussed.
Turning to fracture, specimens of plastic with a sharp notch failed by forming a highly stretched neck-like process zone at the notch tip. Close inspection of notch tip of the plastic material revealed notch blunting and the initiation of a secondary crack inside the process zone. The stress analysis through finite element simulations further revealed that the crack initiation occurs at a location with high stress triaxiality. Bonding a rubber layer is showed to modify the process zone and reduce the magnitude of stress triaxiality in the plastic. The result is a dramatic improvement in flaw tolerance with rubber addition.
Finally, we examined shape-morphing of rubber-plastic laminates. Uniaxially stretching a rubber-plastic bilayer composite beyond its yield point created an elastic strain mismatch between the two layers. Upon release, the bilayer bent out-of-plane. In rubber-plastic bilayers we showed a remarkable dependence of the final shape upon the stretch applied prior to release. All bilayers bent into arch or roll shapes with the plastic on the convex face at a small applied stretch. At a large stretch, the bilayers bent into half-tubes with the plastic, now heavily wrinkled, becoming the concave face. Between these two extremes, saddle shapes appeared that have characteristics of both arches and half-tubes. The flip in shape formed was driven by the significant yielding in compression and formation of plastic wrinkles. A model was developed which predicts these shape changes through energy minimization.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
10 June 2022 |
| Date Type: |
Publication |
| Defense Date: |
31 January 2022 |
| Approval Date: |
10 June 2022 |
| Submission Date: |
24 February 2022 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
175 |
| 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: |
rubber, plastic, composites, necking, flaw tolerance, morphology |
| Date Deposited: |
10 Jun 2022 18:29 |
| Last Modified: |
10 Jun 2022 18:29 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/42265 |
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