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Residual Stresses and Strains in Cross-linked Polyethylene Power Cable Insulation
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The subject of this thesis is modeling of the manufacturing process of high voltage power cables with the aim of predicting residual stresses and strains in the cable insulation. The studied material is cross-linked polyethylene (XLPE), which at room temperature is a semi-crystalline viscoelastic solid. Above the crystallization temperature the material exhibits a rubber type behavior due to the crosslinks.

An extensive set of uniaxial tensile relaxation tests were used for the mechanical characterization of XLPE. These experiments were complemented by pressure volume temperature experiments as well as density and crystallinity measurements. Based on the experiments, initially a linear and later a non-linear viscoelastic power law model was formulated, incorporating temperature and crystallinity dependence. The non-linear model is based on the Schapery formulation. Evaluations of the model were performed with additional uniaxial experiments. These included comparisons between predicted stress responses and measured values during relaxation tests with transient temperature histories, during two step relaxation experiments and during uniaxial tests with constant strain rate loading.

The initial modeling work focused on the prediction of residual stresses which develop during the cooling stage of the manufacturing process. As the constitutive model incorporates temperature and crystallinity dependence, the mechanical problem is coupled to the heat transfer and crystallization problems. Calculations were performed for a vertical manufacturing line. The effects of a viscoelastic material model are illustrated by a comparison to a stress state predicted by a thermo-elastic material model.

A final study concerns the modeling of the residual strains in the insulation. It was found that strains originating at cross-linking of the molecules play a signifi- cant role for buildup of residual strains. Calculations are performed for the same vertical process line as before. Good agreement was found between predicted and experimentally obtained residual strains. Based on the residual strain state an estimate is made for the upper limit of shrink-back of the cable insulation.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 23 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0412
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4020OAI: oai:DiVA.org:kth-4020DiVA: diva2:10426
Public defence
2006-06-13, Sal F3, Lindstedtsvägen 26, Stockholm, 10:15
Opponent
Supervisors
Note

QC 20100915

Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2013-01-14Bibliographically approved
List of papers
1. Viscoelastic model of cross-linked polyethylene including effects of temperature and crystallinity
Open this publication in new window or tab >>Viscoelastic model of cross-linked polyethylene including effects of temperature and crystallinity
2005 (English)In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 9, no 4, 225-246 p.Article in journal (Refereed) Published
Abstract [en]

Characterization of the mechanical behavior of cross-linked polyethylene (XLPE) commonly used in high voltage cable insulation was performed by an extensive set of isothermal uniaxial tensile relaxation tests. Tensile relaxation experiments were complemented by pressure-volume-temperature experiments as well as density and crystallinity measurements. Based on the experimental results, a viscoelastic power law model with four parameters was formulated, incorporating temperature and crystallinity dependence. It was found that a master curve can be developed by both horizontal and vertical shifting of the relaxation curves. The model was evaluated by making comparisons of the predicted stress responses with the measured responses in relaxation tests with transient temperature histories.

Keyword
cross-linked polyethylene, viscoelastic model, power law model, XLPE
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5893 (URN)10.1007/s11043-005-9002-x (DOI)000238138500002 ()2-s2.0-33744957680 (Scopus ID)
Note
QC 20100914Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-14Bibliographically approved
2. Prediction of residual stresses in cross-linked polyethylene cable insulation
Open this publication in new window or tab >>Prediction of residual stresses in cross-linked polyethylene cable insulation
2005 (English)In: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 45, no 8, 1132-1139 p.Article in journal (Refereed) Published
Abstract [en]

Modeling of the manufacturing process of high-voltage power cables was performed with the aim of predicting residual stresses in the cable insulation. A viscoelastic power law-type constitutive model was used which incorporates temperature and crystallinity dependence of the parameters. In this way the mechanical problem is coupled to the heat transfer and crystallization problems. In order to illustrate the effects of relaxation, a comparison to a thermoelastic material model is made.

Keyword
Chemical relaxation, Crosslinking, Crystallization, Electric cables, Electric insulation, Electric potential, Heat transfer, Residual stresses, Thermoelasticity, Viscoelasticity
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5894 (URN)10.1002/pen.20376 (DOI)000231037600011 ()2-s2.0-25144496441 (Scopus ID)
Note
QC 20100914Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-14Bibliographically approved
3. A non-linear viscoelastic constitutive model for XLPE and its application in residual stress prediction for high voltage cable insulation
Open this publication in new window or tab >>A non-linear viscoelastic constitutive model for XLPE and its application in residual stress prediction for high voltage cable insulation
2006 (English)Report (Other academic)
Publisher
17 p.
Series
Trita-HFL, ISSN 1104-6813 ; 2006:09
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5895 (URN)
Note
QC 20100915Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-15Bibliographically approved
4. Residual strains in XLPE high voltage cable insulation
Open this publication in new window or tab >>Residual strains in XLPE high voltage cable insulation
2006 (English)Report (Other academic)
Series
Trita-HFL, ISSN 1104-6813
Series
Royal Institute of Technology, Department of Solid Mechanics, 411
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5896 (URN)
Note
QC 20100915Available from: 2006-06-01 Created: 2006-06-01 Last updated: 2010-09-15Bibliographically approved

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