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3D analysis of deformation and porosity of dry natural snow during compaction
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. (Experimental mechanics)ORCID iD: 0000-0002-5943-1476
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. (Experimental mechanics)ORCID iD: 0000-0001-7395-3302
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. (Experimental mechanics)
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. (Experimental mechanics)
(English)In: Journal of materials science, ISSN 1996-1944Article in journal (Refereed) Submitted
Abstract [en]

The presented study focuses on three-dimensional (3D) microstructure analysis of dry natural snow during compaction. The X-ray computed microtomography (micro-CT) system was used to record 1601 projections of the snow volume. Experiments were performed at four in-situ load conditions as 0 N, 10 N, 18 N and 25 N, to investigate the effects of compaction on structural features of snow grains. The micro-CT system produces high resolution images i.e. 4.3 μm per voxel in 6 hours of scanning time and the equipment was in a cold room at -15◦c. The micro-CT images of the snow illustrate that the grain shapes are mostly dominated by needles, capped columns and dendrites. It was found that the majority of grains appeared to have a deep hallow core irrespective of the grain shape. A digital volume correlation (DVC) method was applied to investigate the displacement fields in the snow volume due to compaction. Results from DVC analysis show that grains close to the punch experience most of the deformation. The reconstructed snow volume is divided vertically into several sections to study the effect of compaction on porosity. It was observed that the porosity (for the whole volume) in principle decreases as the level of compaction increases, however, no clear correlation is found between compaction and porosity with respect to the individual sections. The observations in this work provide a valuable analysis to maximize the understanding of snow microstructure during compaction.

Keywords [en]
Tomography; snow grains; snow microstructure; Digital volume correlation; Porosity
National Category
Other Materials Engineering
Research subject
Experimental Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-68399OAI: oai:DiVA.org:ltu-68399DiVA, id: diva2:1198567
Available from: 2018-04-18 Created: 2018-04-18 Last updated: 2018-04-18
In thesis
1. Experimental investigation of snow metamorphism at near-surface layers
Open this publication in new window or tab >>Experimental investigation of snow metamorphism at near-surface layers
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Experimentell undersökning avsnömetamorfismen vid nära ytskikt
Abstract [en]

Snow metamorphism is a direct objective in many snow research areas, and its charac-terisation is a major challenge in areas including winter road maintenance, detection of icing on wind turbine blades, and snow quality mapping for skiing. A common effect of snow metamorphism is compaction, which can be investigated from the associated vari-ations in physical properties of snow. While the relation between snow metamorphism and physical properties of snow is fairly well-known, a method to quantify this relationis not extensively researched. This experimental based thesis focuses on the relationship between the physical properties of snow and its degree of metamorphism. The link isestablished and investigated by quantifying near-infrared (NIR) reflectance measure-ments and analysing the microtomographic data. Three experimental approaches are developed to record the NIR reflectance measurements and to understand the influence of compaction at near-surface layers of a snowpack. In addition, an X-ray microtomogra-phy (micro-CT) system is used to visualise the behaviour of snow microstructure during compaction. In this thesis, snow experienced compaction via aging, the melting-freezing process, uniaxial loading, settling and infiltration of liquid water.

A numerical tool based on the well-established Discrete Ordinates Radiative Trans-fer (DISORT) method is used to solve the radiative transfer equation (RTE) for aplane-parallel and semi-infinite snowpack. The numerical solver takes the reflectance measurements as input and returns the coefficients of a first order Legendre phase function of an investigated snowpack at a given wavelength of light. The results from the solver show consistency and strong correlation between the Legendre coefficient sand the physical properties of snow. Furthermore, the physical properties of snow such as specific surface area (SSA) and liquid water content (LWC) were estimated via parameterisation where the reflectance data is used as input. The results suggest that the parameterisation of LWC can provide a qualitative estimate of the LWC in a snowpack, while the parameterisation of SSA provides a quantitative estimate of the snow SSA. As a next step, the influence of compaction on snow microstructure is investigated from three-dimensional (3D) images obtained using the micro-CT system. In this case, compaction is initiated by applying uniaxial load on a snow sample and the effect of compaction is analysed based on digital volume correlation (DVC) and porosity distribution. The micro-CT observations further emphasise that near-surface layers of a snowpack experience a higher degree of impact during compaction.

In summary, this thesis presents experimental methods to quantify the link between snow compaction at near-surface layers, and the physical properties of snow. The mode observations show that the estimated Legendre coefficients can provide qualitative descriptions of snow grain distribution and surface texture. The parameterisation methods can provide the details about the LWC and the SSA of a snowpack. Further, the observations from the micro-CT study suggest that grains breakage and recrystallisation are the prevailing effects of snow compaction. All observations in this thesis are helpful in understanding the metamorphism in a snowpack for relevant research areas.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
Snow metamorphism; NIR reflectance; Snow and Ice; Radiative transfer equation; Paramterization; Snow properties; Tomography; Snow microstructure
National Category
Other Materials Engineering Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-68394 (URN)978-91-7790-116-7 (ISBN)978-91-7790-117-4 (ISBN)
Public defence
2018-06-18, E 231, Luleå University of Technology, Luleå, 14:00 (English)
Opponent
Supervisors
Available from: 2018-04-18 Created: 2018-04-18 Last updated: 2018-05-29Bibliographically approved

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