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An Experimental Study on the Inflation of Non-Elastic Tubes

Pazin, Jack W (2024) An Experimental Study on the Inflation of Non-Elastic Tubes. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abstract

Previous studies observed that tubes may experience localized bulging if sufficiently inflated. In hyperelastic tubes, it has been found the presence of a pressure maximum in the pressure-volume response predicts the formation of bulging instabilities during inflation. Also, previous research found that a hyperelastic material’s strain hardening behavior can be used to predict bulge formation and that sufficient strain hardening can prevent bulging. However, research on bulging instabilities in non-elastic tubes is limited. In this thesis, polyurethane and low-density polyethylene (LDPE) tubes subjected to volume-controlled inflation. Results from the polyurethane inflation tests found irregular bulging that was influenced by viscoelasticity and loading history. Further tests found that viscoelasticity influences the formation of irregular bulges since higher flow rates tend to result in fewer irregularities. This is because the viscous component dominates at lower flow rates and allows for more irregularities to develop due to the slow drop in pressure. Tests also found that previous loading cycles cause strain induced damage. Due to the bulges that form during inflation, the amount of strain-induced damage from previous inflation cycles is not uniform. This causes bulges from previous inflation tests to be exaggerated when samples are re-inflated. The irregularities were axisymmetric and small amounts of plasticity were present when inflated to high volumes. In LDPE tubes, a single nonaxisymmetric bulge appeared followed by rupture shortly after. These tubes showed large amounts of plasticity and smaller viscoelastic effects when compared to polyurethane. When an external limiter was added to simulate a sudden application of high amounts of strain hardening, the nonaxisymmetric bulge propagated instead. The bulge’s propagation velocity was proportional to the volumetric flow rate and decreased with an increasing limiter diameter. The pressure at which the bulge propagated also decreased with increased limiter diameter. Cross sections of the samples showed that the nonaxisymmetric bulges were caused by necking instabilities in the tangential direction.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Pazin, Jack Wjap424@pitt.edujap424
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairVelankar, Sachin Shankarvelankars@gmail.com
Committee MemberSmolinski, Patrickpatsmol@pitt.edu
Committee MemberSchmidt, DavidDES53@pitt.edu
Date: 6 September 2024
Date Type: Publication
Defense Date: 29 April 2024
Approval Date: 6 September 2024
Submission Date: 1 May 2024
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 143
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Mechanical Engineering
Degree: MSME - Master of Science in Mechanical Engineering
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Instability, Plasticity, Polyurethane, LDPE, Viscoelasticity, Damage
Date Deposited: 06 Sep 2024 19:57
Last Modified: 06 Sep 2024 19:57
URI: http://d-scholarship.pitt.edu/id/eprint/46636

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  • An Experimental Study on the Inflation of Non-Elastic Tubes. (deposited 06 Sep 2024 19:57) [Currently Displayed]

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