Type: Article
Title: Effects of thermal and mechanical cyclic loads on polyurethane pre‐insulated pipes
Authors: Doyle Gutierrez, Lucia 
Weidlich, Ingo 
Issue Date: 2-Dec-2020
Keywords: district heating; polyurethane; sandwich structure
District heating (DH) pre-insulated pipes are a sandwich assembly composed by a steel heat service pipe, polyurethane (PU) foam and polyethylene casing. The foam acts as bond between the steel pipe and casing. The application has high constraints for the foam, as it is subjected to cyclic multiaxial stresses, high cyclic temperatures and long expected service life. In this study, we evaluate if and how cyclic loads affect the shear strength, shear modulus, toughness and failure behaviour of the PU foam in DH pipes sandwich assembly compared with unaged reference samples. We have found that the simultaneous application of mechanical and thermal loads weakens the strength and increases the stiffness of the foam and that this change is not caused by degradation of the molecular structure. Crack initiation and propagation along the pipe samples follow a very consistent pattern between samples, with cracks initiating in Mode II and propagating in Mode I. The consistent axial displacement of approximately 2 cm from each other suggests the formation of strain localizations.
Subject Class (DDC): 624: Ingenieurbau und Umwelttechnik
HCU-Faculty: Technisches Infrastrukturmanagement 
Journal or Series Name: Fatigue & fracture of engineering materials & structures 
Volume: 44
Issue: 1
Start page: 156
End page: 168
Publisher: Wiley
ISSN: 1460-2695
Publisher DOI: 10.1111/ffe.13347
URN (Citation Link): urn:nbn:de:gbv:1373-repos-7384
Directlink: https://repos.hcu-hamburg.de/handle/hcu/586
Language: English
Creative Commons License: https://creativecommons.org/licenses/by/4.0/
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