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The vibrational properties of spruce (Picea abies Karst.) and European beech (Fagus sylvatica L.) were investigated in this study in dependence on the relative humidity (RH). The RH was measured at 20 °C ranging from oven-dried to 85%. For the evaluation of the vibrational properties the dynamic modulus of elasticity E’ and the damping coefficient tan δ were measured at 7 climate steps. The same samples used for the vibrational tests were afterwards mildly thermally modified at 180 °C and measured at the same climate steps. Both wood species were compared and evaluated considering the property changes (E’, tan δ, sorption isotherms and volume swelling) due to the thermal modification. The chosen modification resulted in a marginal change in the vibrational properties of spruce, whereas the properties of beech were clearly changed. The vibrational properties of beech could be improved in the usual RH range (35–85%) due to this thermal modification. For spruce, it was concluded that a mild modification, conducted in this study, is not suitable for improving the vibrational properties. Further conclusions concerning the underlying causes as well as the use in musical instruments were drawn.

The aim of this work is to establish a bending test method as evaluation criteria for mechanical properties (strength and modulus of elasticity) of veneers. The bending test is one essential and ea...

In this study, the relatively new picture frame method applied to wood is compared with three established shear test methods, namely the experimental modal analysis, the square plate twist method and the torsion test. For the investigations, the wood species European beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) were used and the shear tests were conducted in LR and RL direction. The results show comparable shear moduli for beech and spruce in the range of 931–1289 Nmm−2 and 495–842 Nmm−2, respectively. In contrast to the theory of linear elastic orthotropic materials, significant differences in the results of the picture frame method between LR and RL direction were observed for spruce.

The mechanical properties of cured wood adhesive films were tested in a dry state by means of nanoindentation. These studies have found that the application of adhesives have an effect on the accuracy of the hardness and elastic modulus determination. The highest values of hardness among the tested adhesives at 20 °C have condensation resins: MF (0.64 GPa) and RPF (0.52 GPa). Then the decreasing EPI (0.43 GPa), PUR (0.23 GPa) and PVAc (0.14 GPa) adhesives. The values of the elastic modulus look a little bit different. The highest values among the tested adhesives at 20 °C have EPI (11.97 GPa), followed by MF (10.54 GPa), RPF (7.98 GPa), PVAc (4.71 GPa) and PUR (3.37 GPa). X-ray micro-computed tomography was used to evaluate the adhesive joint by the determination of the voids. It has been proven that this value depends on the type of adhesive, glue quantity and reactivity. The highest values of the void ratio achieve the PUR (17.26%) adhesives, then PVAc (13.97%), RRF (6.88%), MF (1.78%) and EPI (0.03%). The ratio of the gaps increases with the higher joint thickness. A too high proportion of voids may weaken the adhesive joint. Validerad;2023;Nivå 2;2023-01-01 (johcin)

A new method for the determination of shear modulus and shear strength is presented in this study using a shear or picture frame. A shear frame in accordance with DIN SPEC 4885 is in other fields, such as fibre reinforced composites, state of the art. Here, a square test specimen with recessed corners is held in the shear frame and subjected to a quite uniform shear deformation state. To determine the shear modulus and the shear strength, tensile load acting on the shear frame and the associated shear strain are measured. This method has the advantage of simultaneous determination of the shear modulus and the shear strength. Thin square wooden plates of European beech (Fagus sylvatica L.) were tested in all anatomical directions. The results show good accordance with literature values. The highest values of shear modulus and shear strength were yielded for the LR plane, followed by the values in the LT plane. The tests in the RT plane clearly resulted in the lowest values.

Untreated and thermally modified woods of cherry, service tree, pear and plum were investigated as potential substitutions for Indian rosewood in guitar making. Acoustic properties such as dynamic modulus of elasticity, dynamic shear modulus in LR-plane and loss coefficient as an indicator for damping were determined by means of experimental modal analysis and the mechanical properties by means of static bending and hardness test. The swelling behavior was also investigated. The results suggest that cherry and service tree could be used as alternative back and side material and plum and service tree may also be used for fingerboards. Thermal modifications at 160 °C for 8 h improve swelling behavior, mechanical properties, but damping was slightly increased for cherry and pear. No significant change of Brinell hardness was observed owing to thermal modification.

Water vapor sorption surface areas and sorption energies of untreated and thermally modified Norway spruce [Picea abies (L.) Karst.], sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelcior L.) were investigated by means of dynamic vapor sorption (DVS) measurements and excess surface work (ESW) evaluation method, respectively. Adsorption and desorption experiments in the hygroscopic range and desorption tests from water saturation were conducted. Thermodynamically, ESW is the sum of the surface free energy and the isothermal isobaric work of sorption. From the amount adsorbed in the first minimum a specific surface area similar to the BET surface area can be obtained. The results show that untreated spruce has a significantly higher specific water vapor sorption surface and sorption energy compared to both hardwoods maple and ash. Thermal modification of the woods leads to a significant reduction of water vapor sorption surface and sorption energy. The determined surface area and energy are higher in desorption direction than in adsorption direction, whereby the highest values in desorption direction from water saturation, especially for maple and ash, were obtained. The surface areas calculated by means of the ESW method are similar to the surface areas calculated by means of the BET method, particularly in adsorption direction.

This research investigated the effect of different fractions of commercial wood flour (Type c100 from JRS, Germany) on mechanical and physical properties of wood-polymer composites (WPC). The fractions were named regarding the mean lengths of their particles in µm; 80, 130, 255, 405 and 485. The composite samples were manufactured with 30 wt% of wood flour fractions of all five groups as well as the not fractionated flour, and 70 wt% of cellulose propionate (CP). The melt mass-flow rate (MFR) of the different granules, tensile strength, and modulus of elasticity, flexural strength, flexural modulus and the impact strength of the injection molded specimens as well as the water uptake were determined in this study. WPCs with the specific size range used in this investigation exhibited improved strength and modulus of elasticity in tensile and flexural tests, compared to pure CP. Using fraction 255, the mechanical properties increased the most. Tensile strength rose by 28 and 13% compared to CP and to WPC with the not fractioned wood powder, respectively. Fraction 255 increased flexural strength by 33 and 5% compared to CP and WPC with the not fractioned flour. The MFR (tested at 190 °C with 7.16 kg) of WPC_255 is the lowest with 2.3 g/10 min. Composites with the smallest particles showed the least water uptake.

During the manufacture of veneers cracks and other damages occur. These damages impair and reduce the veneer cross-section. By means of microscopic investigations cracks and damages in veneer cross-sections were documented and measured. These investigations were conducted with industrially sliced 0.3, 0.6 and 1.2 mm thick veneers. The results determine the residual cross-sections in dependence of veneer thickness which can be used for numerical calculations.

Large string instruments, such as cellos and double basses, are manufactured, bought and played all over the world. Thereby they are exposed to different climate conditions. This paper describes shape alterations using the example of a double bass stored at different climatic conditions. By means of an optical measurement these shape alterations were recorded and represented. The results clearly show spots with strong and without deformations. Thus, weak points of the construction are localised and improvements can be established for the construction of string instruments.

Milling is one of the most important cutting procedures in the wood industry. It allows shaping of workpiece surfaces with a high chip-removal rate. This is possible because of a fast rotary cutting motion, the possibility to place many cutting edges on the tool circumference and a fast linear feeding motion. Due to these different kinds of motions the resulting effective motion follows a prolonged cycloid which forms periodic waves on the workpiece surface. These surface patterns, called cuttermarks, may be visible on the machined surface after cutting and mainly influence the workpiece quality. Further surface machining steps are required to meet the demanded standards of surface quality. This is why researchers have been looking for possibilities to lower or avoid these cuttermarks. Beside the description and the analyses of the geometry of cuttermarks, magnitudes of disturbance, mechanical and mechatronic approaches and alternative procedures will be introduced and discussed. Especially mechat...

The possibility of the use of thermally modified European beech (Fagus sylvatica L.) in necks of electric bass guitars for the substitution of Hard maple (Acer saccharum) has been studied. The heat treatments were performed at relatively mild treatment temperatures of 140 and 160 °C for 12 h. The acoustic properties were determined by means of experimental modal analysis (EMA) and the mechanical properties by means of static and impact bending tests. The results show that both the acoustic and mechanical, static properties of beech improve significantly owing to thermal modification, being similar or better compared to Hard maple. The impact bending strengths decrease owing to thermal modification. Additional tests on complete necks of electric bass guitars by means of EMA and plucking tests on total instruments show that thermally treated beech at mild temperatures can substitute Hard maple for the use as neck material in electric bass guitars.

This paper deals with the determination of the pore-size distribution of untreated and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.) and sycamore maple (Acer pseudoplatanus L.) by means of mercury intrusion porosimetry. The investigations considered oven-dried and at 22 °C and 95 % relative humidity-conditioned samples. A special sample holder and a novel method for evacuation were developed for the measurements. This was necessary both to ensure that samples were positioned at a defined distance and the conditioned samples did not dry in an uncontrolled manner. The results clearly show that the climatic state influences the results. Thermal modification greatly alters the pore-size distribution of spruce. This can be largely attributed to the formation of intercellular spaces in the middle lamella as a result of cell-wall compression due to thermal modification. The alteration of the pore structure of maple due to thermal modification is not as pronounced as that of spruce.

The aim of this paper was to investigate pore-size distributions in the nano-diameter range of wood and their alteration due to thermal modification of wood using thermoporosimetry, and to find out what consequences can be derived regarding the biological durability. Thermoporosimetry is a technique that is based on the measurement using differential scanning calorimetry (DSC). The method is based on the fact that frozen water contained within small pores is at elevated pressure and therefore has a depressed melting temperature as a function of the appropriate pore diameter. In addition, the fiber saturation points (FSP) were determined by DSC. The former were performed in an isothermal-step method and the latter using the continuous heating-up method. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), Sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelsior L.) were analyzed. The results clearly show that the pore shares of wood for the measurable diameter range between 4 and 400 nm decrease considerably in all studied wood species due to thermal modification of the wood. Furthermore, thermal modification of wood leads to a decreased FSP for all studied wood species. For evaluation as well as reproducibility of the results of pore-size distribution and FSP, the consideration of sensible heat and specific heat of fusion plays an important role. If this is not done, it can lead to misinterpretations.

The main objective of this study was to evaluate the effect of sample preparation on cell-wall density and porosity using gas pycnometry. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), sycamore maple (Acer pseudoplatanus L.), and European ash (Fraxinus excelsior L.) were analyzed. The samples differed in terms of shape, geometry, and climatic state. On the one hand, the samples were oven dry as usual and, on the other hand, conditioned at 22 °C and 95 % relative humidity. Furthermore, the samples were processed using solvent exchange drying. In addition to helium, nitrogen was used as a displacement gas. The tests show i.a. how this can lead to misinterpretation of the cell-wall density or porosity of wood determined by gas pycnometry. The results show that native spruce has a lower cell-wall density and higher porosity compared with native maple and ash. Due to thermal modification, the cell-wall densities are decreased. The investigations show that the determined cell-wall density and porosity of the wood are strongly dependent on the sample geometry and climatic state. The cell-wall densities of all investigated wood species in the conditioned state at 22 °C and 95 % relative humidity are significantly higher compared with the oven-dry cell-wall densities.

Wood furfurylation is a modification method that improves several wood properties. Thereby wood is impregnated with a solution of furfuryl alcohol, catalysts and water, in general. The objective of this study was to understand the penetration of furfuryl alcohol into wood. Furthermore, a possible relationship between the substance amount and the swelling behaviour should be determined. To this end microscopic investigations were conducted to describe the temporal process of penetration and swelling. It was found that the swelling coefficients differ at the microscopic and macroscopic level. The microscopic swelling can reach twice the values of macroscopic swelling.

A new design of a milling cutter with solid helical edge has been developed for improving the performance of cutting wood. Development of the new helical edge milling cutter with its geometries for planing wood has been followed by some research progresses. In this work, a conventional edge milling cutter and helical edge milling cutters were tested in planing spruce wood (Picea abies). The purpose of the research work was to investigate chip flow, power consumption, noise emissions, edge wear, and surface roughness characteristics of the helical edge milling cutters in planing spruce wood. Experimental results showed that the helical edges compared to the conventional edge milling cutter provide better chip flows with nearly axial direction and low flight velocity. Though the extreme helical edges up to 75° inclination angle generate comparable or slightly larger cutting power than the conventional edge, they considerably generate lower sound pressure level of up to 5 dB(A). The helical edge milling cutters are better in wear resistance, suffer less edge fractures, and produce better surface quality of planed wood than the conventional edge milling cutter.

International audience; The aim of this work was to analyse the material behaviour of thermally modified and native spruce by load applied perpendicularly to the grain. Therefore, thermally modified and native samples were prepared for bending tests with the load in tangential direction. The bending strength in radial direction decreases significantly with the thermal treatment. The fracture surfaces in the tangential section of the bending samples after testing were analysed with a scanning electron microscope. For native samples, the typical failure was found in the intercellular area. For thermally modified samples, failure of the entire cell wall was observed. The material behaviour is more brittle, as demonstrated by the load-deflection curves, but also by anatomical studies of the fracture surfaces.

The characterization and removal of odorous substances caused by thermal treatment of wood were investigated using chromatographic and spectroscopic methods. Emissions of pentanal and hexanal, probably formed by oxidation of unsaturated fatty acids, were the prevailing aldehydes in untreated wood samples. Their amount decreased during thermal treatment, while furfural and 5-methylfurfural (degradation products of hemicelluloses) accounted for almost 100% of the aldehyde fraction. Furthermore, it can be assumed that odorous emissions of thermally modified wood can be strongly reduced by solvent extraction. An ethanol–cyclohexane mixture that produces wood samples without significant odour emissions obtained good results. Certain organic solvent extractives from thermally modified beech have fungicidal properties. Methanol extracts, resolubilized in propanone, caused a retardation of fungal growth on native beech specimens. Beech specimens impregnated with these extractives could be assigned to dur...

Bending and tensile tests were carried out on veneer of beech (Fagus sylvatica L.) and European oak (Quercus robur L./Quercus petraea Liebl.) with a thickness between 0.35 mm and 0.5 mm. The tests were done on veneer in two test series, one parallel to the fibre and the other one perpendicular to the fibre. Mechanical properties and bending radiuses were measured and evaluated. It could be concluded that the bending properties of the veneers not only depend on the bending stiffness but also the mechanical strength and structure of the material. During the tests it could be shown that the 3-point bending test procedure is not a suitable method for determining the bending modulus of rupture.

During the coating of multidimensional moulded surfaces the coating material suffers different stresses, which limit the possible mould. The behaviour of veneer as a thin coating material is discussed in the following article. The investigations were carried out with veneers of beech (Fagus sylvatica L.), sycamore maple (Acer pseudoplatanus L.) and American walnut (Juglans nigra L.) of different thicknesses. The anisotropy of the material is analysed concerning the various structure of the considered wood species. Feasibilities and limits of a three dimensional moulding are presented and conditions for a plastic deformation are discussed.

Ziel der dargestellten Arbeit war die vergleichende Untersuchung thermisch modifizierter und unmodifizierter Zwillingsproben aus Fichtenresonanzholz fur Gitarrendecken. Durch eine thermische Modifikation konnen die physikalisch-technischen Eigenschaften des Resonanzholzes derartig verandert werden, dass sie den Erfordernissen des Musikinstrumentenbaus besser entsprechen als unmodifizierte Proben. Vor allem sind dies die reduzierte Wassersorption, grossere Dimensionsstabilitat, hohere Dauerhaftigkeit aber vor allem auch die Verbesserung von akustischen Kennwerten. Der Einfluss einer relativ milden thermischen Modifikation auf das Resonanzholz kann mit einer “kunstlichen” Alterung verglichen werden. Das Holz erfahrt durch die Modifikation eine Verbesserung objektiv messbarer Kennwerte, welche auf ein verbessertes Klangverhalten schliessen lassen.

Colorimetric measurements are often carried out for evaluation of colour changes on wooden surfaces. However, a grading of the value $\Delta E^{*}_{\mathrm{ab}}$ , (colour difference) is missing for wooden surfaces. Colour measurements were carried out on surfaces of six wood species. It could be shown that there is a native colour difference within wooden surfaces which is influenced by the texture of the wood. This native colour difference has a magnitude of $\Delta E^{*}_{\mathrm{ab}}$ of about 2.

The modulus of elasticity of weakly thermally modified as well as native twin samples of spruce was determined at different air humidity levels. Within the range of 0 and 93% of relative humidity a higher modulus of elasticity could be proven for thermally modified samples than for native comparison samples. The functional interrelation between modulus of elasticity and wood moisture admitted for native woods could be confirmed for modified twin samples.

Tensile tests on walnut burl veneer (Junglans nigra L.) were carried out in different directions. The modulus of rupture, the modulus of elasticity and the elongation of rupture were determined from the veneers tested. Thereby a dependence on the direction was found. The values determined differ up to 30% in dependence of the direction of cutting and the development of cracks connected with the production of the veneers.

International audience; For the production of spliced veneers the veneers are coated with thin cellulose fleece or special paper layers, and thereby thin composites are generated. This article describes the mechanical properties of such a composite material consisting of 0.35 mm beech ( L.) veneer and a 0.12 mm cellulose fleece bonded with a PVAc adhesive.

The milling process of Arboform was analysed by cutting force measurements and compared with experiments on MDF and chipboard. Under similar and practice-specific conditions, the specific cutting forces of Arboform were slightly higher than the ones of MDF and chipboard but below the values for HDF taken from literature.

The aim of this work was to examine the pulping process of wood and annual plants by use of an extruder. The fibrous materials manufactured in the extruding attempts were examined, compared and evaluated on the basis of different testing methods. An analysis and a characterisation of the fibrous materials could be proven using this method.