WOOD RESEARCH Volume 64, Number 5, 2019
Ondřej Schönfelder, Aleš Zeidler, Vlastimil Borůvka, and Lukáš Bílek

Impact of silvicultural measures on the quality of scots pine wood Part II. Effect of site

This study deals with the variability of wood density, compression strength and the impact bending strength within the trunk of Scots pine (Pinus sylvestris L.). The impact of the site on the examined properties was also evaluated. The tree samplers come from four different sites that are representative for Scots pine growth in the Czech Republic. From the samplers the sections representing a basal part of the trunk and a middle part of the tree were cut. The most significant influence of the site was confirmed for wood density; on the other hand, the influence of the site is ambiguous in terms of the examined strength characteristics. A decrease in the wood properties with increasing trunk height was proven for all tested properties. The highest impact of the position was observed for wood density, while the results of vertical variability in mechanical properties are not always significant (compression strength: basal 47.1 MPa and middle 45.8 MPa). A close correlation between mechanical properties and wood density was also proven.

WOOD RESEARCH Volume 65, Number 6, 2020
Rudolf Petráš, Julian Mecko, Danica Krupová, and Pažitný Andrej

Aboveground biomass basic density of hardwoods tree species

The influence of tree species on basic density of wood, bark and small-wood was investigated here. Experimental material was obtained from 73 trees of 7 tree species, namely alder (Alnus glutinosa (L.) Gaertn.), beech (Fagus sylvatica L.), birch (Betula pendula Roth.), hornbeam (Carpinus betulus L.), Black locust (Robinia pseudoacacia L.), Sessile oak (Quercus petraea (Matt.) Liebl.) and Turkey oak (Quercus cerris L.) from the territory of Slovakia. Wood and bark samples were taken from discs cut from three trunk sections and from small-wood and branch parts coming from tree crowns. The volume of green samples was measured in graduated cylinders with a precision of 1 ml; a dry matter was measured with a precision of 0.01 g. The statistically significant effect has been shown in tree species, biomass fractions and locations on the tree. The average basic density of all species varies from 440 to 650 kg.m-3 for wood, for bark it is 380-670 kg.m-3 and for small-wood outside bark it reaches 490-650 kg.m-3. Alder and Black locust tree species have the lowest and highest wood density, Black locust and Turkey oak of bark and alder and Turkey oak of small-wood.

WOOD RESEARCH Volume 64, Number 4, 2019
Ondřej Schönfelder, Aleš Zeidler, Vlastimil Borůvka, and Lukáš Bílek

Impact of silvicultural measures on the quality of Scots pine wood. Part I. effect of regeneration method

This study deals with the influence of the silvicultural measures on selected mechanical properties of Scots pine (Pinus sylvestris L.) wood in the Czech Republic. Sample trees were selected at two different localities that are characteristic of Scots pine growth, and they represent two different Scots pine regeneration methods, namely the clear-cutting and shelterwood regeneration method. We tested compressive strength and impact bending strength. The density of the wood was also evaluated as a factor influencing strength characteristics. The shelterwood regeneration method shows higher values in most of the investigated characteristics (49.3 MPa for the shelterwood method and 44.6 MPa for the clear-cutting method in the case of compressive strength); however, these differences are not significant for the processing industry. Another positive effect of the shelterwood regeneration method is the even distribution of the properties within the trunk in radial direction in contrast to clear-cutting method.

WOOD RESEARCH Volume 64, Number 4, 2019
Paweł Czarniak, Karol Szymanowski, Jacek Wilkowski, Jarosław Górski, and Fabrice Dagrain

Machinability characterization of solid wood with scratching and drilling techniques

This paper describes the characterization of four wood species (alder, oak, jatoba and obeche) with regards to their machinability, i.e. susceptibility to mechanical processing expressed by different machinability indicators. Three types of tests were performed. Drilling tests were conducted on a computer numerical control (CNC) working center as well as on a conventional vertical drilling machine. Both machines were fully instrumented with transducers to continuously measure the torque and the thrust force while drilling. Scratching tests were performed on an instrumented shaper, allowing continuous measurement of the normal and tangential components of the total force applied on a cutter while cutting. This resulted in correlations between particular machinability indicators that were estimated with usage of different measurement benches. Moreover, machinability indicators obtained in this way were compared to the mechanical properties of the wood species. Especially strong correlations were obtained with density or strength in static bending. Those alternative techniques were to some extent coincidental. Particularly, similar results occurred with assessments on CNC machine indicators (torque and thrust force) and friction coefficients (MIε-drilling) during drilling on a conventional drilling machine or indicator C2. The necessity of some improvements in fitting the geometry of an elementary cutter regards to specific properties of solid wood proved in described below experiments should result in higher reliability and usefulness of testing method.

WOOD RESEARCH Volume 64, Number 4, 2019
Li W. G. and Zhang Z. K.

The effect of micro-pits texture on the coefficient of friction between wood and cemented carbide under different wood moisture content

Friction is an important factor during cutting of wood. Micro-texture has been proven to be an effective measure for the improvement of material friction performance. This paper investigates the effect of the cemented carbide surface micro-pits texture on the performance of wood cutting tools with the purpose to reduce the coefficient of friction on knife/workpiece contact zone. Birch (Betula spp.) and pine (Pinus sylvestris) were selected as the research object, the impacts of wood moisture content and the load used on the friction coefficient of different micropits structures were assessed and compared. We found that at a diameter of the micro-texture of 60 μm, the coefficient of friction can be effectively reduced at different wood moisture contents. The average friction coefficient between cemented carbide and wood surface increased with increasing moisture content below fiber saturation point (FSP). But the increase in free water quantity can lead to a more considerable decrease in the friction coefficient. At a higher working load, the value of the average coefficient of friction between the surfaces increases.

WOOD RESEARCH Volume 65, Number 4, 2020
Roman Fojtík, Viktor Dubovský, Kateřina Kozlová, and Lenka Kubíncová

Prestress losses in spruce timber

Prestressing force and its change is one of the key factors that affect wooden constructions, especially those using methods of transverse prestressing. To achieve a description of a prestress force (P) in transversally prestressed wooden constructions a simulated experiment was done. Prestressing force, external temperature, and moisture were measured during 669 days. The main goal of this article was to model the primary losses of the prestress force at the spruce element of the 138 x 138 mm cross-section with the sensor installed. For this purpose, all measurements were statistically analyzed and the period of primary loss was found. During this period the prestress force was decreasing with time mainly and the influence of temperature and moisture could be omitted. Based on this analysis a mathematical model of losses of the prestress force was found as P = 8.538-0.014.day.

WOOD RESEARCH Volume 65, Number 3, 2020
Darius Albrektas, Milda Jucienė, Vaida Dobilaitė, and Raimondas Bliūdžius

The influence of thermal modification on the resistance to water impact properties and strength of wood used in outdoor conditions

In this study the influence of thermal modification on the resistance of wood to the impact of water and mechanical properties and to compare the durability of thermally modified and coated wood products operating in wet conditions was investigated. It was found that the weight of thermally unmodified non-coated oak wood after 48 h of soaking increased on average up to ~ 15%, and the weight of coated oak wood increased up to ~ 8%. If wood was thermally modified, the weight of non-coated oak wood increased up to ~ 9%, and the weight of coated oak wood increased up to ~ 5%. After 168 h of soaking these change is about 2 times larger. In the case of pine wood compared to oak wood these change of weight after 48 h is about 2.0 – 2.4 times and after 168 h about 1.4 – 2.0 larger. It can be stated that wooden constructions intended to be used in very wet conditions should be made of thermally modified wood without coating. Thermally modified wood will have greater dimensional and shape stability. Thermal modification reduces the swell up to 1.6 times in the case of oak, more than 2 times in the case of pine.

WOOD RESEARCH Volume 65, Number 3, 2020
Candan Kus Sahin, Mehmet Topay, and Ahmet Ali Var

A study on suitability of some wood species for landscape applications: Surface color, hardness and roughness changes at outdoor conditions

In this study, each of the commonly used two types of woods (softwood and hardwood) from five species was studied. All wood species show a systematic trend to change to higher values of surface roughness with natural weathering progress. The Black pine, Calabrian pine and beech wood samples show a more or less smooth trend, whereas basswood gives the highest surface roughness changes under all conditions. However, the hardwood species, except basswood, have higher hardness properties both initially and at the end of weathering process when compared to softwoods. The surface discoloration that occurs is clearly visible as a natural texturing. However, the degree of, and the pattern of texturing, may vary with different kinds of woods; the color changes also vary to some extent. It was revealed that the discoloration is strongly dependent on the botanical origin of wood species. The lower lightness changes (ΔL %) were found for all three pine species (16.2 to 37.2%) when compared to fir (54.9%) and spruce samples (91.8%). The Scotch pine wood showed highest values for the contribution of red color initially and low redness change on the surface after the weathering process, among the other softwood species.

WOOD RESEARCH Volume 65, Number 2, 2020
VLADIMÍR IHNÁT, HENRICH LÜBKE, Balberčák Jozef, and Kuňa Vladimír

Size reduction downcycling of waste wood. Review

The article includes research related to utilization of waste wood which is primarily size reduced due to its voluminity for next processing for lower value added products for about last twenty years. Procedures and results obtained by different authors were considered in one study. In this review a wood waste downcycling was consider as a process of transformation of large size wood products over their lifetime to the new products, where a size reduction is one of the first operations needed to achieve to. Incineration of each way was excluded from the present review, but second-generation biofuels are considered as potential products for the future. Two points of research selection according to origin and according to products made of waste wood was applied in this review. Comparison shown that the most industrially applicable implementation of treated particles obtained from waste wood is intended to the composite materials production as particleboards, fibreboards, cement-bonded and wood-plastics.

WOOD RESEARCH Volume 65, Number 2, 2020
Sinn Gerhard, Jürgen Maierhofer, Dieter Loidl, Stephan Puchegger, and Stefanie Stanzl-Tschegg

Elastic constants of six wood species measured with the resonant beam technique

The elastic properties of six wood species were determined using the resonant beam technique. By stimulation of transverse vibrations and analyzing the responding oscillations of carefully prepared rectangular beams of wood, simultaneous determination of one Young’s modulus and two shear-moduli on one specimen is possible. Using three different cutting orientations along the principal material directions all three Young’s moduli and three shear moduli can be determined. This paper presents the application of this technique to six wood species: two softwoods, two hardwoods and two tropical woods.

WOOD RESEARCH Volume 65, Number 1, 2020
Candan Kus Sahin and Busra Onay

Alternative wood species for playgrounds wood from fruit trees

A number of orchard woods have been investigated for suitability in the playgrounds, in the view of responders. In this sense, photos were taken of the specially prepared samples as stimuli, and there were three different groups of respondents. It was observed that the participants were effective in terms of age grouping and material preferences. For group A and C, majority of the participants preferred wooden elements for playground material. However, the majority of participants in group B (50.5%) preferred plastic elements, followed by wooden (31.5%), and then metal (18.0%). Moreover, it was seen that the most significant factors for selection of material for a playground should be safety for both Group A (79%), and C (76.5%), whereas it was aesthetic appearance, for group B (71%). Similar results were found for color properties of wood — the majority of participants of all three groups preferred light colored wooden elements in playgrounds. The results for the aesthetic preferences of wood species judged one-by-one and judged together received similar results. The preference scores for fig wood (Figus canica) is significantly higher than for other wood species, while “wood color” and “aesthetic appearance” are reliable positive predictors to aesthetic preferences.

WOOD RESEARCH Volume 65, Number 1, 2020
Anderson Renato Vobornik Wolenski, Rodrigo Guerra Peixoto, Veronika Fedotova, André Luis Christoforo, and Francisco Antonio Rocco Lahr

Short note: Shear strength estimation model for tropical wood species

For safety reasons, wood strength values are calculated based on their characteristic values. Brazilian national standard (NBR, in Portuguese “Norma Brasileira Regulamentadora”) 7190 (1997) establishes ratios for characteristic strength estimation and three forms of wood characterization, with an emphasis on the simplified procedure for common species, which allows obtaining the strength characteristic values through equations correlating different mechanical properties. The present work evaluates the accuracy of the relation proposed by NBR 7190 (1997) of shear strength along the grain (fv0,k) to compression strength along the grain (fc0,k) (fv0,k=0.12 fc0,k). 960 experimental measurements of shear and compression strength values were performed for 40 hardwood species, and the precision of the relation proposed by the Brazilian standard was evaluated using the analysis of variance (ANOVA) method. Linear, exponential, logarithmic, and geometric regression models were used as an alternative to the NBR relation for shear strength estimation. The statistical analysis revealed that the geometric regression is the model of best fit.

WOOD RESEARCH Volume 66, Number 3, 2021
Huijun Dong, Mohsen Bahmani, Miha Humar, and Sohrab Rahimi

Fiber morphology and physical properties of branch and stem wood of hawthorn (crataegus azarolus l.) grown in zagros forests

This study aims at investigating the effect of three altitude levels (below 1800 m, 1800-2000 m and above 2000 m) on the physical and biometric properties of stem-wood and branch-wood of hawthorn species. Moreover, the relationship between wood dry density and volumetric swelling, fiber length, fiber diameter, cell wall thickness were studied. Results indicated that altitude had significant effects on the dry density, volumetric swelling and fiber length of stem wood while did not significant effects on the density of branch wood. Additionally, some physical and biometric properties had relatively greater correlation coefficients in branch wood than in stem wood whereas others had higher coefficients in stem wood compared to branch wood. Deep understanding of properties this wood species will provide a fresh insight into the relationship between wood properties and environmental factors.

WOOD RESEARCH Volume 64, Number 3, 2019
Hung-Chi Su, Shu-Fen Tung, Chun-Ta Tzeng, and Chi-Ming Lai

Variation in the charring depth of wood studs inside wood-frame walls with time in a fire

In this study, the variation in the charring depth of wood studs inside wood-frame walls (WFWs) in a fire was investigated. First, the time variation in the surface temperature of wood studs inside WFWs was determined based on ISO 834 fire-resistance tests, and the resulting heating conditions were used in subsequent heat exposure tests. Then, wood stud specimens of four different wood species (Chinese fir, Japanese cedar, Southern pine and spruce) were each subjected to a heat exposure test in an electric furnace. The results exhibited no significant correlation between the charring depth of the wood stud specimens and the preheating density. In addition, the test data validated that the equation proposed by Sugahara can be used for predicting the charring depth of wood studs inside WFWs in a fire.

WOOD RESEARCH Volume 64, Number 3, 2019
Roman Fojtík

Moisture content analysis of wooden bridges

The article deals with assessing the impact of moisture content conditions in wood mass of the wood bridges constructions on their lifespan in Central Europe. Wood moisture content as one of main factors influencing the wooden elements mechanical properties was studied on seventeen wooden bridge constructions. The dependence of temperature and relative humidity on material moisture content was observed in summer season and also in winter season. The lifespan of historical and modern wood structures was discussed as well.

WOOD RESEARCH Volume 64, Number 2, 2019
Ngargueudedjim Kimtangar, Guersoube Tao, and Guy Edgard Ntamack

Study of the correlation between fiber and mechanical properties of wood Borassus aethiopum Mart. of chad

Palmyra palm (Borassus aethiopum Mart.) is a large palm tree whose wood is often used for its mechanical resistance and weathering in buildings in Africa. In this work, the influence of fibre characteristics on the mechanical properties of wood was studied. For this purpose, the mechanical characteristics were determined and study of the micrograph of the sapwood and Duramen which are the useful parts of this wood were carried out. The results of this study show the mechanical properties of the palmyra are very influenced by the number and the mechanical characteristics of the fibres. The proposed polynomial model of the evolution of the mechanical characteristics gives the good results because the maximum relative mistakes of the prevision are 4.43% for the breaking strength and 0.40% for the Young’s modulus.

WOOD RESEARCH Volume 64, Number 1, 2019
S. Sadiye Yasar

Effects of wood preservatives on the combustion process and combustion quality of wood

This study examines the combustion properties of Scots pine (Pinus sylvestris L.) and Oriental beech (Fagus orientalis L.) in 3 stages (CWF, SC and EC) according to ASTM E 160-50 (1975). Wood samples were impregnated with Tanalith-E (T) and Wolmanit-CB (WC) and then were varnished with Synthetic (St) and water based (wb) varnishes. When the combustion was completed, the weight loss, combustion temperatures, illuminance values, total time of combustion, and demolition time were measured. As the result, illuminance value of Oriental beech wood decreased, while the smoke density increased. Scots pine was later destroyed in the combustion process. Areas with a risk of fire are advised to use pine wood instead of beech. Wolmanit-CB and synthetic varnish reduced the temperature and illuminance values. Oriental beech, Tanalith-E, and synthetic varnish resulted in the highest temperatures for all combustion stages. This triple interaction increased total combustion time values by more than 90% when compared with the control samples.

WOOD RESEARCH Volume 66, Number 1, 2021
Minghua Wang, MING LI, TINGTING DENG, SAIYIN FANG, Xiaosong Li, and Fei Lai

Study on lamb wave propagation characteristics along the grain of thin wood sheet

Through the time-frequency analysis of the propagation waveform of the acoustic emission (AE) signal propagating in the thin sheet of Pinus sylvestris var. mongolica, the propagation characteristics of the stress wave when propagating as a lamb wave was studied. An AE source was generated on the surface of the specimen, the discrete wavelet transform method was used to achieve AE signal de-noising and reconstruct the waveform of the AE signal. On this basis, the time difference positioning method was used to calculate the propagation velocity of lamb waves, and compared with the propagation characteristics of lamb waves in the metal specimen. The results show that the high-frequency mode of lamb waves attenuated sharply as they propagate in the thin wood sheet, indicating that the microstructure of wood has a significant low-pass characteristic for lamb waves. The average attenuation rates of lamb waves in metal and thin wood sheet were 87.1% and 75.7%, and the velocity was 4447.0 m.s-1 and 1186.3 m.s-1, respectively. This shows that AE signals can travel longer distances in the thin wood sheet, but the propagation velocity is significantly reduced.