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  • 1
    Electronic Resource
    Electronic Resource
    Chemical and physical changes required for producing dimensionally stable wood-based composites (1989)
    Springer
    Wood science and technology 23 (1989), S. 281-288 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary High temperature (240°C) contact treatment was shown to be a very effective method of stabilizing panels bonded with heat resistant adhesive. Chemical analyses of post treated boards indicate that chemical changes of the wood components due to contact heat treatment were negligible. The results support the concept that high temperature post treatment of boards at temperatures above the softening points of lignin and carbohydrate components, caused plastic flow in situ which relieved internal stresses built up during hot pressing. Consequently, springback in wood-based composites diminished leaving panels much more stable than conventional products. Also, dimensionally stable wood-based composites had a better inherent ability to withstand severe exposure conditions than the regular boards.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00367742
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Chemical and physical changes required for producing dimensionally stable wood-based composites (1988)
    Springer
    Wood science and technology 22 (1988), S. 281-289 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The springback of compressed wood caused by built-up internal stresses results in excessive thickness swelling of wood-based composites when exposed to moisture. Steam pretreatment can cause partial hydrolysis of hemicellulose for both hardwoods and softwoods which markedly increases the compressibility of wood and in turn significantly reduces the build-up of internal stresses in composites during hot pressing. This steam pretreatment process is a very effective method for producing dimensionally stable wood-based composites. Mild steam pretreatments (e.g. 3 to 4 min at 1.55 MPa) cause a significant reduction of the water insoluble xylan content in hardwoods and the amount of xylan, mannan and galactan in softwoods without any apparent changes in the cellulose or lignin content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386023
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  • 3
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    Boundary stresses due to impacts from dry granular flows (2012)
    Wiley
    Details
    Publication Date: 2012-05-23
    Description: Field data and laboratory experiments suggest that bedrock wear from debris flows is largely due to particle–bed impacts, rather than solely due to abrasion by sliding, and that the associated bedrock erosion rates are dependent on the particle size distribution in the debris flow. Here we use Discrete Element Method (DEM) simulations with an established contact mechanics model to explore grain-size influences on contact forces associated with particle–bed impacts in sheared granular mixtures. We first compare DEM simulations with experimental observations obtained from shallow granular flows in rotating drums of diameters 0.56 m and 4.0 m. Our simulations reproduce, without parameter tuning, experimentally measured segregation, boundary pressures, and height profiles. We perform additional simulations systematically varying particle size distributions in binary mixtures. We show that local time-averaged boundary pressures in thin flows are essentially the normal component of the weight of the flow, independent of particle size distribution. However, other statistical measures of boundary forces scale with mass-averaged particle size. We demonstrate that this is because individual particle–bed impacts, rather than impacts from multiple particle collisions, dominate the largest contact forces. We show that these largest impact forces vary as the square of grain size and the 1.2 power of impact velocity as predicted from the contact mechanics model underlying the DEM. These results support the particle size dependence of a recently proposed bedrock incision model and suggest that next steps for a predictive bedrock incision model require the statistics of the largest impact velocities.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Mean and fluctuating basal forces generated by granular flows: laboratory observations in a large vertically rotating drum (2014)
    Wiley
    Details
    Publication Date: 2014-05-14
    Description: A flowing granular mass generates forces on the boundary that drive near-bed grain dynamics, bed surface erosion, and energy dissipation. Few quantitative analyses exist of the controls on the dynamically fluctuating force caused by granular flows with wide grain-size distributions and a liquid phase in the pores. To study the mechanisms controlling the boundary forces, we used a 225 cm 2 load plate to measure the bed-normal force from a suite of granular flows in a 4-meter-diameter, 80-cm-wide vertically rotating drum. We analyzed the time series of bed forces generated in flows composed of granular material for both narrow (gravel-water) and wide (muddy, sand-gravel-cobble) grain-size distributions. The tail of the force distribution was captured more closely by a generalized Pareto distribution than an exponential distribution, suggesting a way to predict empirically the force distribution. We show that the impulse on the bed, related to kinetic energy transferred to the bed from the granular collisions, is quantified by the standard deviation of the force. The mean bulk force equaled the static weight of the flow, whereas the force fluctuations, represented by the standard deviation and the averaged top 1% of force, were a near-linear function of effective grain diameter and flow velocity, and a ~0.5 power function of an inertial stress scaling term. The force fluctuations depend on both Savage and Bagnold numbers. The correlations revealed in this study suggest that it may be possible to estimate dynamic forces on the bed from gross properties of the flows.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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