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- Girlanda, Orlando, et al.
(författare)
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Analysis of the Micromechanical Deformation in Pressboard performed by X-ray Microtomography
- 2015
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Ingår i: IEEE Electrical Insulation Conference (EIC). - Piscataway, NJ : IEEE Communications Society. - 9781479973545 ; , s. 89-92
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Konferensbidrag (refereegranskat)abstract
- A large number of electrical insulation components are produced in paper-based materials. Paper combines good insulating properties with the necessary mechanical and chemical stability. Paper consists of a system of fibers binding to each other creating a strong network. The presence of large open pores allows for impregnability of the material but also causes mechanical weakness in particular in the out-of-plane direction of the material. This aspect is important for pressboard components, where the resistance to compression stress is relevant for e.g. transformer windings. It is therefore relevant to understand the mechanisms that underlay the out-of-plane deformation of pressboard. In order to get a clear picture of the deformation patterns within the material, X-ray micro-computed tomography was used. Pressboard test pieces were subjected to in-situ out-of-plane compressive loading. 3D images of the sample could be captured before, during and after the loading sequence. Image analysis allowed for the definition of strain fields. The results revealed a strong correlation between the density variation within the sample and the strain calculated from the 3D images.
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| 2. |
- Joffre, Thomas, 1987-, et al.
(författare)
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A 3D in-situ investigation of the deformation in compressive loading in the thickness direction of cellulose fiber mats
- 2015
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 22:5, s. 2993-3001
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Tidskriftsartikel (refereegranskat)abstract
- Fiber mat materials based on cellulose natural fibers combines a useful set of properties, including renewability, stiffness, strength and dielectric insulation, etc. The dominant in-plane fiber orientation ensures the in-plane performance, at the expense of reduced out-of-plane behavior, which has not been studied as extensively as the in-plane behavior. Quantitative use of X-ray micro-computed tomography and strain analyses under in-situ loading open up possibilities to identify key mechanisms responsible for deformation. In the present investigation, focus is placed on the out-of-plane deformation under compressive loading of thick, high density paper, known as pressboard. The samples were compressed in the chamber of a microtomographic scanner. 3D images were captured before and after the loading the sample. From sequential 3D images, the strain field inside the material was calculated using digital volume correlation. Two different test pieces were tested, namely unpolished and surface polished ones. The first principal strain component of the strain tensor showed a significant correlation with the density variation in the material, in particular on the top and bottom surfaces of unpolished samples. The manufacturing-induced grooves generate inhomogeneities in the microstructure of the surface, thus creating high strain concentration zones which give a sensible contribution to the overall compliance of the unpolished material. More generally, the results reveal that, on the micrometer scale, high density fiber pressboard behaves as a porous material rather than a low density fiber network.
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