Dry Spruce Research Articles

Mechanics of Screw Joints Solved as Beams Placed in a Tangential Elastic Foundation

This article deals with a new original analytical solution of deformation, force and stress states in wood screw joints up to the limit values of pulling out/breaking the screw. The screws are under tension. The wood-to-screw interaction is effectively simplified by introducing several physical model variants using a tangential elastic non-linear foundation. The experimental verification of the proposed models using pull-out tests (i.e., pulling out screws from dry spruce wood in laboratory conditions) confirms the correctness of the proposed models of the elastic linear/non-linear foundation. The validity of the model is also analytically and experimentally verified in the biomechanical model of pulling out screws from the femur of a bovine/human cadaver, which confirms and expands the validity of newly designed screw joint models outside the timber structure area.

Diptera in clear-felling stumps like it dry

ABSTRACTWhen stumps on clear cuts are harvested for bioenergy, retention of a share of them is recommended to mitigate environmental issues. To maximise benefits for the diversity of saproxylic beetles, retention should be done in dry positions. Saproxylic dipterans are usually thought to be associated with wetter wood substrates. We therefore hypothesised that dipterans would benefit from other recommendations. We tested that by rearing out insects from spruce and birch stumps sampled in clear fellings, and received a material of 866 individuals of 24 Diptera taxa. Among six Diptera species tested statistically, one was associated with dry stumps when comparing within spruce, and the total abundance of dipterans was higher in dry spruce stumps than in wet. No parameter (total species number, species number per stump, total abundances and abundances of individual species) showed a higher value for wet stumps than for dry. We conclude that there are several Diptera species that frequently use stumps, of which a large share was earlier regarded as very rare. For those, our hypothesis was falsified, as the affinities to dry stumps seem similar as for beetles and the same recommendations could be used.

Highly effective impregnation and modification of spruce wood with epoxy-functional siloxane using supercritical carbon dioxide solvent

Chemical modification of wood is an established approach to improve its biological durability, water repellence, dimensional stability, and UV resistance. Norway spruce wood (Picea abies) in dry state, however, has an extraordinarily high recalcitrance towards impregnation with liquid modification reagents as drying triggers the irreversible closure of pits, i.e. the cell-to-cell valves in softwood. In the present study, it is shown that supercritical carbon dioxide is a highly suitable impregnation medium to overcome the recalcitrance of dry spruce wood. This has been exemplarily demonstrated for deca(dimethylsiloxane)-α,ω-diglycidylether (D8M 2 OG ), a linear oligosiloxane with terminal epoxy-functionalities, which could be loaded into respective wood samples affording a weight gain of up to 63%. The thermally assisted reaction of the epoxy-functional siloxane with the wood polymers was catalysed with ring-opening Tin (II) octoate. The effort resulted in a remarkably reduced wettability with water, as evident from contact angle measurements (~ 140°), and in a significant decrease (≤ 20%) of the sample’s sensitivity towards moisture-induced dimensional changes.

Microwave testing of moist and oven-dry wood to evaluate grain angle, density, moisture content and the dielectric constant of spruce from 8\xa0GHz to 12\xa0GHz

The scope of this work is to discuss the challenges and demonstrate the potential of microwave testing for applications in the wood processing industry. Microwave technology benefits from the anisotropic dielectric properties of wood to simultaneously identify grain angle, density, and moisture content of wood. Therefore, the theory of free space transmission measurement is thoroughly discussed with emphasis on the characteristics of (and how to deal with) reflections occurring in real measurements. A more sophisticated calculation method for the derivation of the desired physical wood properties is presented. The advantages of a modern laboratory style setup are shown and its possible transition in an industrial-style application is discussed. Moist (moisture content 7.6–14%) and oven-dry spruce samples are tested. The detection of grain angle for moist and oven-dry wood yields an RMSE (root-mean-squared-error) of 0.14° and 0.4°, respectively. Moisture content is evaluated with density- and thickness-independent methods. Adapted regression models are proposed yielding an RMSE for moisture content of 0.45% for a single frequency measurement. The promising advantages of wood moisture estimation with frequency sweeps instead of fixed frequency signals are discussed and demonstrated for all samples (RMSE 0.39%). The dielectric constant of moist and oven dry spruce in the range from 8 to 12 GHz is evaluated in respect to density, moisture content and temperature. The respective constants ε′, ε′′, and tan(δ) are formulated in a general form via a non-linear regression and compared to existing data in literature.

Emissions of Nanoparticles from Small Combustion Equipment with Regard to the Combustion Mode and Wood Humidity

Contamination of air by solid particles is serious problem for human health and also environment, especially in certain regions of the Czech Republic and Poland. Small particles in nano-sizes are more dangerous than same weight of larger size. Negative effect namely of the solid particles depends on number, specific surface area, respirability and bonding of others substances (e.g. PAH, As, Cd, Zn, Cu etc.) which are higher for smaller (nano-sizes) particles compared to larger one. With the approaching winter, yearly problems with distribution of particles from small combustion equipments arise. The annual emission balance indicate that the proportion of small sources to total air pollution (PAH, dust) is surprisingly expressive [1]. For this reason mentioned above this contribution deals with measuring of amount, and distribution of nanoparticles produced form combustion of wood in small combustion unit. <br />For combustion test in grave-free stoves were used three samples of wood (wet spruce, dry spruce and raw spruce) and two combustion modes. Nanoparticles from flue gas were characterized by the aperture low-pressure cascade impactor DLPI (separation and weighing of particles in sizes 30 ηm ÷ 10 µm). Wood were combusted in the form of ¼ logs.

Modeling carbon dynamics in two adjacent spruce forests with different soil conditions in Russia

Abstract. Net ecosystem carbon exchange (NEE) was measured with eddy covariance method for two adjacent forests located at the southern boundary of European taiga in Russia in 1999–2004. The two spruce forests shared similar vegetation composition but differed in soil conditions. The wet spruce forest (WSF) possessed a thick peat layer (60 cm) with a high water table seasonally close to or above the soil surface. The dry spruce forest (DSF) had a relatively thin organic layer (5 cm) with a deep water table (>60 cm). The measured multi-year average NEE fluxes (2000 and –1440 kg C ha−1yr−1 for WSF and DSF, respectively) indicated that WSF was a source while DSF a sink of atmospheric carbon dioxide (CO2) during the experimental years. A process-based model, Forest-DNDC, was employed in the study to interpret the observations. The modeled multi-year average NEE fluxes were 1800 and –2200 kg C ha−1yr−1 for WSF and DSF, respectively, which were comparable with observations. The modeled data also showed high soil heterotrophic respiration rates at WSF that suggested that the water table fluctuation at WSF could have played a key role in determining the negative carbon balance in the wetland ecosystem. A sensitivity test was conducted by running Forest-DNDC with varied water table scenarios for WSF. The results indicated that the NEE fluxes from WSF were highly sensitive to the water table depth. When the water table was high, the WSF ecosystem maintained as a sink of atmospheric CO2; while along with the drop of the water table the length of the flooded period reduced and more organic matter in the soil profile suffered from rapid decomposition that gradually converted the ecosystem into a source of atmospheric CO2. The general effect of water table variation on wetland carbon balance observed from this modeling study could be applicable for a wide range of wetland ecosystems that have accumulated soil organic carbon while face hydrological changes under certain climatic or land-use change scenarios.

Urea-melamine-formaldehyde (UMF) resin penetration in medium-density fiberboard (MDF) wood fibers

Confocal microscopy has been used to investigate the behavior of urea-melamine-formaldehyde (UMF) resin after being sprayed onto wood fibers. Samples of wood fibers were dyed with Toluidine Blue O (TBO) to create a contrast between the resin and the fiber when studied under a confocal laser scanning microscope (CLSM). The resin droplet penetration into the fiber cell wall was evaluated from the three-dimensional images generated by the CLSM. Experimental conditions were varied to determine their influence on the penetration of the resin into the cell wall. The Washburn equation was used to model the penetration process. The model takes into account variations of the resin viscosity with temperature and time. The penetration rate was found to be related to resin viscosity. The penetration depth can be as low as 1 μm if the resin is applied on a dry spruce fiber in a drum mixer. The maximum penetration depth corresponds to the thickness of the cell wall, which can vary from 10 to 20 μm for spruce. Further work should lead to the development of a more effective resin that could be used to make boards with the same performance but less resin.

Distribution with depth of protozoa, bacteria and fungi in soil profiles from three Danish forest sites

The numbers and biomass of protozoa, bacteria and fungi were measured at various depths (1.5–122.5 cm) in the unsaturated zone of three contrasting pristine Danish forest site profiles: a dry beech ( Fagus silvatica) forest on mor, a wet peaty spruce ( Picea abies)/birch ( Betula pubescens) forest and a dry spruce ( P. abies) forest on mor. All sites were situated on a Weichel moraine. Except for a bacterial peak at 42.5 cm in the peat profile, the general tendency was a decrease in biomass with increasing depth for all groups examined. Protozoa decreased more rapidly with increasing depth than the other two groups of organisms examined. An evaluation of the bacterial–protozoan relationship by a simple mathematical model indicated that the subsurface protozoan populations are active and not accidental percolated cysts. The low protozoan numbers found in shallow subsurface sites contrast markedly with the results from contaminated sites where much larger protozoan populations have been reported even at considerable depths. Consequently, the results suggest that protozoa are good indicators of organic pollution in subsurface soils; however, more work involving the comparison of polluted and unpolluted soils is needed to confirm this suggestion.