| 1. |
- Girlanda, Orlando, et al.
(författare)
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Characterization and Modelling of the Mechanical Properties of Pressboard
- 2013
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Ingår i: 2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP). - : IEEE. - 9781479925964 ; , s. 563-566
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Konferensbidrag (refereegranskat)abstract
- Cellulose-based components constitute the bulk of the current insulation for transformers. Cellulose is an organic polymer material which combines excellent electrical properties and good mechanical performance. As a polymeric material, cellulose is very sensitive to moisture and temperature. These factors can influence the electrical and mechanical performance of a transformer throughout its lifetime. In order to ensure the quality of the product during transformer manufacturing, as well as during transformer life-time services, adequate models for predicting the physical properties of its constituents are needed. The present investigation tackles the mechanical description of pressboard. For this purpose, a three dimensional mechanical model is developed for simulating the in-plane and out-of-plane behavior of the pressboard material. The model is based on an anisotropic viscoelastic-viscoplastic constitutive law, which includes features that are particular for cellulose-based materials, e.g. the peculiar double nature of fiber-network-based and porous material. The material is orthotropic by nature, i.e. the in-plane mechanical properties markedly differ from the out-of-plane ones. Particular regard is taken when considering the effect of out-of-plane stresses which both cause viscous deformation and permanent compaction. The analyses on the mechanical behavior of pressboard are performed by comparing the experimental data on pressboard and the results of model simulations.
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| 2. |
- Girlanda, Orlando, et al.
(författare)
-
Modeling and experimental validation of the mechanical behavior of pressboard
- 2014
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Ingår i: Proceedings of the 2014 Electrical Insulation Conference. - : IEEE conference proceedings. ; , s. 203-207
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Konferensbidrag (refereegranskat)abstract
- High density (HD) pressboard is an essential element in power transformers combining good electrical insulation properties with effective mechanical characteristics that well suit design requirements of power transformers. In order to ensure a correctly functioning transformer, it is therefore very important to characterize and to understand the mechanical properties of pressboard under different operating conditions. Pressboard is composed of natural polymeric chains, whose mechanical properties are affected by moisture and temperature. Moreover, temperature and moisture conditions in power transformers vary throughout manufacturing process and service/operation life-time. An accurate definition of the mechanical properties is, therefore, necessary.The present article focuses on the effect of different combinations of temperature/moisture and mechanical load on the deformation behavior of HD pressboard samples. A mechanical constitutive model is developed for finite element (FEM) simulation based on a viscoelastic–viscoplastic material description. Special attention is given on the complex through-thickness deformation behavior of HD pressboard. Thorough analyses are performed based on the comparisons between the results of experimental characterization and FEM modeling and simulations. The good agreement between experimental and modeling results shows a great potential for application in mechanical design of transformer insulation.
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| 3. |
- Girlanda, Orlando, et al.
(författare)
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On the transient out-of-plane behaviour of high-density cellulose-based fibre mats
- 2016
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 51:17, s. 8131-8138
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Tidskriftsartikel (refereegranskat)abstract
- High density cellulose-based materials have been widely used for electrical insulation and (interior) construction or structural material. Similar to typical paper/board materials, the microstructure of high-density fibre mats consists of a porous network of cellulose fibres, which contributes to its highly non-linear mechanical response. Such fibre mats exhibit strong anisotropic material behaviour as well as significant transient (time-or rate-dependent) behaviour. The present investigation is aimed at studying the transient behaviour of high-density cellulose fibre mats, particularly during out-of-plane compression. A viscoelastic-viscoplastic constitutive model dedicated for high-density cellulose-based materials has been used to simulate the responses of the high-density cellulose-based fibre mats upon two types of transient loading, i.e. compressive creep and stress relaxation. The predictions of the model are then compared to the corresponding experimental characterization results, which indicate that material densification mechanism plays a more critical role during out-of-plane compression creep than in stress relaxation.
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