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Local moisture content and swelling strain in wood investigated by NMR and X-Ray microtomography

TL;DR: In this article, the swelling properties of wood in relation to its moisture content were studied by using non-invasive methods, such as Magnetic Resonance Imaging MRI and volumetric digital image correlation (V-DIC).
Abstract: The aim of this paper is to study the swelling properties of wood in relation to its moisture content by using non-invasive methods. The NMR methods lead to determine, on the one hand, the distribution of the moisture content in the sample (by Magnetic Resonance Imaging MRI) and, on the other hand, the evolution of the water into the porous network (by longitudinal relaxation time T1). X-Ray microtomography observations coupled with volumetric digital image correlation (V-DIC) give access to 3D-displacement fields from which local strain heterogeneities have been derived. It is shown that deformation is non homogeneous in relation to the moisture content in early and latewood.
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TL;DR: In this paper, a scaling law for the deflection of a board is proposed, which is seen to be followed qualitatively but not quantitatively by experiments, which allows upscaling of deflection and expansion, such that behavior of thick boards can be determined from an experiment using a thin board.
Abstract: When a wood board is exposed to a change in relative humidity on only one of its surfaces, eg in case of flooring or a panel painting, the resulting asymmetric moisture content profile induces differential expansion over the thickness Consequently a bending moment causes the board to curve A theory is presented to describe the bending of a wood board due to a step change in relative humidity The board is assumed to be homogeneous, isotropic, and linearly elastic Moisture transport is presumed to obey the diffusion equation with constant coefficients, such that moisture transport can be directly related to the bending of the board It is shown that the transient deflective behavior provides the diffusion coefficient and the final length change yields the linear hygroscopic expansion coefficient Derived diffusion coefficients are in good agreement with values in literature Furthermore, a scaling law for the deflection of the board is proposed, which is seen to be followed qualitatively but not quantitatively by experiments Finally, by assuming the deflection of the board to be the response of a linear system, the deflective frequency response of the board can be predicted from its step response The results allow upscaling of deflection and expansion, such that behavior of thick boards can be determined from an experiment using a thin board

13 citations


Cites background from "Local moisture content and swelling..."

  • ...optical sensor [21], or a combination of NMR and X-ray microtomography [22]....

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Journal ArticleDOI
TL;DR: In this paper, the authors used step response to predict the bending of a panel painting subject to a change in the ambient relative humidity (RH) in terms of frequency and amplitude for different board thickness.
Abstract: Panel paintings are essentially wooden boards painted on one side. Due to the vapor resistance of the paint layer, changing ambient conditions lead to exchange of moisture on only one surface. Subsequently, a non-uniform moisture content profile is formed across the thickness of the board. As a result, differential expansion causes the board to bend in case of no mechanical restriction, or it leads to a build-up of stresses inside the material if restrained. Experiments with oak boards sealed on one side and exposed to a change in the ambient relative humidity (RH) were performed. By scaling, the response of any board with different thickness can be predicted. Since the bending of the board can be described as a linear system behavior, the frequency response can be predicted based on the step response. In combination with critical strains for wood and gesso from the literature, this gives insight into allowable RH fluctuations in terms of frequency and amplitude for different board thicknesses.

5 citations


Cites background from "Local moisture content and swelling..."

  • ...…changes in RH have been studied extensively, both experimentally (Chomcharn and Skaar 1983; Schellen 2002; Bratasz et al. 2010; Senni et al. 2010; Caré et al. 2012; Derome et al. 2012; Gauvin et al. 2014; Lanvermann, Wittel, and Niemz 2014) and numerically (Gloimüller et al. 2012; Rafsanjani et…...

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Journal ArticleDOI
TL;DR: In this paper, the authors describe cyclic variations in the ambient relative humidity, composed of a wide variety of frequencies, and show that variations may be as fast as one minute or as slow as a complete season.
Abstract: Fluctuations in the ambient relative humidity are often cyclic of nature, composed of a wide variety of frequencies. Variations may be as fast as one minute or as slow as a complete season....

1 citations


Cites background from "Local moisture content and swelling..."

  • ...Many experimental studies on hygroscopic expansion of wood consider only stepwise changes in the relative humidity (Zhou et al. 1999, Murata and Masuda 2006, Senni et al. 2010, Caré et al. 2012, Derome et al. 2012, Gauvin et al. 2014)....

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04 Jul 2010
TL;DR: In this paper, the authors discussed the factors influencing the durability of glued assemblies of wood and cementitious material under variable hygrometric conditions, and showed that there are restrained deformations at the glue interface and that the cement paste is damaged.
Abstract: This paper discusses the factors influencing the durability of glued assemblies of wood and cementitious material under variable hygrometric conditions. The composite specimens are composed of cement paste connected to plywood using epoxy glue. The cement paste is subjected to autogeneous shrinkage and the wood is subjected to imbibition test. Plywood is used so that the swelling deformations due to the imbibition process are parallel to the connection plane. Swelling strains in wood are related to the water content measured by gammadensimetry technique. Global strains above and below the glue interface have been measured and have been compared to the free strains. We showed that there are restrained deformations at the glue interface and that the cement paste is damaged. Local strains have been characterized by means of the digital image correlation technique. We showed in particular that the deformations in wood are related to the microstructure of the layers of plywood and that the restrained deformations at the glue interface lead to a bending of the cement paste. In the case of strong adhesion properties, this bending induces cracking in cement paste.
References
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01 Aug 2007-Strain
TL;DR: In this article, a set of triaxial compression tests on specimens of argillaceous rock were performed under tomographic monitoring at the European Synchrotron Radiation Facility in Grenoble, France, using an original experimental set-up developed at Laboratoire 3S.
Abstract: A set of triaxial compression tests on specimens of argillaceous rock were performed under tomographic monitoring at the European Synchrotron Radiation Facility in Grenoble, France, using an original experimental set-up developed at Laboratoire 3S, Grenoble Complete 3D images of the specimens were recorded throughout each test using X-ray microtomography Such images were subsequently analysed using a Volumetric Digital Image Correlation software developed at the Laboratoire de Me?canique des Solides in Palaiseau, France Full-field incremental strain measurements were obtained, which allow to detect the onset of shear strain localisation and to characterise its development in a 3D complex pattern Volumetric Digital Image Correlation revealed patterns which could not be directly observed from the original tomographic images, because the deformation process in the zones of localised deformation was essentially isochoric (ie without volumetric strain), hence not associated to density changes

352 citations

Journal ArticleDOI
TL;DR: While latewood undergoes similar strains in the transverse directions, earlywood radial strains are less than a third of the tangential strains, and the less homomorphic and smaller swelling/shrinkage of earlywood in radial direction is found to be caused by the presence of rays.

117 citations

01 Jan 2004
TL;DR: In this article, surface digital image correlation techniques are extended to the analysis of volume data obtained from X-ray computed tomography with micrometric resolution or serial reconstruction obtained under plane laser illumination for transparent materials.
Abstract: Surface digital image correlation techniques are extended to the analysis of volume data obtained from X-ray computed tomography with micrometric resolution or serial reconstruction obtained under plane laser illumination for transparent materials. The local image contrast is provided by markers much smaller than the characteristic dimensions of the gradients to analyze and which do not disturb notably the latter, as checked by numerical simulations. In case of computed tomography, small dense particles are randomly added, while optical scatterers are used in transparent materials. The resolution of the displacement measurement, evaluated on rigid body motions, can be close to 0.01 voxel but can be strongly degraded on noisy images. New matching criteria, less sensitive to noise, are proposed and discussed. Presented applications concern plastic homogeneous flat or notched samples under tension, as well as particulate metal matrix composites.

81 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used Magnetic Resonance Imaging (MRI) and validated these results with oven-drying methods and analyzed the cement paste porosity modifications due to drying exposure with distribution of T1 relaxation times.

63 citations

Journal ArticleDOI
TL;DR: In this paper, the microscopic swelling behavior of latewood tracheid was observed using confocal laser scanning microscopy and the digital image correlation method, which indicated that the cell arrangement was strongly influenced by the macroscopic/mesoscopic structure.
Abstract: In order to study the transverse swelling/shrinkage of wood, the microscopic swelling behavior of latewood tracheid was observed using confocal laser scanning microscopy and the digital image correlation method. A microcrater structure was created on the surface of the specimen by using the ion sputter etching technique to obtain a pattern-rich digital image for image analysis. Douglas fir specimens were conditioned by two methods of absorption: rapid absorption of moisture from hot steam, and slow absorption of moisture from the water vapor of saturated solutions. Latewood tracheid near the surface of the specimen deformed only in the radial direction when the relative humidity of the surrounding air changed rapidly (rapid absorption of moisture from hot steam or absorption/desorption of moisture during the observation). In addition, the diameter of the lumen decreased upon rapid absorption of moisture, whereas it expanded upon slow absorption of moisture. These results indicate that the microscopic swelling behavior of latewood cells is strongly influenced by the macroscopic/mesoscopic structure, for instance, the cell arrangement or the alternation of latewood and earlywood.

49 citations