共查询到20条相似文献，搜索用时 31 毫秒
1.
《Scandinavian Journal of Forest Research》2012,27(3):241-249
The Brinell hardness and equilibrium moisture content (EMC) were measured from thinning-aged silver birch wood. Wood material both from the trees harvested in the first commercial thinning and from trees remaining on site after the thinning was included. The average Brinell hardness was 19.40 MPa. It correlated significantly with the basic density of wood. With respect to the distance from the pith, the Brinell hardness of air-dried wood was higher than that of artificially dried wood. The average EMC of the conditioned (20°C, 65% relative humidity) wood was 12.0%. The EMC of the wood also varied, with the EMC being higher for air-dried wood than for kiln-dried wood. EMC was the highest at a distance of 30–40 mm from the pith, decreasing towards both pith and log surface. Seasonal variation in both the Brinell hardness and the EMC of the wood was found. It was presumed to be a consequence of season-dependent physiological changes in trees. 相似文献
2.
Density profile relation to hardness of VTC wood composites was evaluated using X-ray densitometry and modified Brinell hardness
method using different applied forces. Moreover, surface elasticity was evaluated. Prior to lamination, the low-density hybrid
poplar (Populus deltoides × Populus trichocarpa L.) and Douglas-fir (Pseudotsuga menziesii L.) thin boards were compressed to 1.22 or 1.14 g/cm3, respectively. Two different kinds of laminations were made, either single layer of 1.5 mm thickness or two 1.5-mm layers
bonded to unmodified wood. The results show that thicker laminate has a great positive influence on Brinell hardness. This
study suggests that results from the existing method for Brinell hardness are not comparable, and if applied force is chosen
without restraint, the effect on the hardness value is significant for inhomogeneous wood composites. 相似文献
3.
Manon Vincent Queju Tong Nasko Terziev Geoffrey Daniel Cecilia Bustos William Gacitúa Escobar Isabelle Duchesne 《Wood Science and Technology》2014,48(1):7-22
Nanoindentation is a powerful tool for hardness testing on a very small scale. Since the technique was first introduced for studying wood cell wall mechanics, it has been integrated as an important tool for measuring the modulus of elasticity and hardness of wood cell walls. In this study, hardness measured with nanoindentation (nanohardness) was compared with hardness measured by the standard Brinell test method (Brinell hardness) on jack pine (Pinus banksiana Lamb.) wood. Nanoindentation was performed on both the S2 layer of the secondary cell wall and the middle lamella (ML) of early- and latewood fibers. Four annual growth rings were studied. The influence of growth ring and initial spacing on both measurements was analyzed. The relationship between Brinell hardness, nanoindentation measurements, and average ring density was also studied. Results suggest that Brinell- and nanohardness are controlled by different mechanisms and factors. The location of nanohardness measurements (i.e., S2 layer or ML) also influenced hardness differently. It was concluded that nanomeasurements are not an exact representation of wood mechanical properties conducted at the macro level because of the hierarchical structure of wood. The effect of other factors such as moisture or wood extractive content may also need consideration. 相似文献
4.
Effects of semi-isostatic densification of wood on the variation in strength properties with density
The variation in strength properties with density was compared between semi-isostatically densified and non-densified wood.
Strength properties were compared with published data from earlier studies using other methods for densification. Small clear
specimens of eight species were analysed for compression strength in axial, radial and tangential direction, three-point bending
and Brinell hardness. After densification, all tested strength properties increased with density, but especially strength
perpendicular to grain became lower than expected from the density of non-densified wood. Strength of densified wood relative
to what could be expected for non-densified wood of similar density was denoted as ‘strength potential index’. For axial compression
strength and bending strength, strength potential index of individual wood species varied between 0.7 and 1.0, i.e. densified
wood is slightly weaker than what could be expected from its density. Strength potential index was lower for properties much
determined by strength perpendicular to grain. In radial direction, densified wood was rubbery with low modulus of elasticity
and nearly no proportional limit or modulus of rupture. Generally, wood was apparently weakened in proportion to the degree
of compression in respective direction. Strength potential index also increased with increasing original density of the species. 相似文献
5.
6.
Formation of benzyl esters from acetic and formic acids during heat treatment of birch at 160–200°C has been studied by gas chromatography. High concentrations of formic and acetic acids formed by the wood itself during hydrothermal treatment were found. The concentrations of acids increased with both treatment time and temperature. The maximum formic- and acetic acid concentrations found at 180°C and after 4 h of treatment performed in this work were 1.1 and 7.2%, based on dry-weight wood, respectively. The treated wood material was characterised by mechanical testing [bending tests perpendicular to the grain, modulus of rupture, modulus of elasticity, Brinell hardness, impact bending and colour measurements (CIE colour space)]. The experiments, where high concentration of acids was formed, showed severe losses in mass and mechanical strength. Indications of possible enhanced mechanical properties for the treated, compared with untreated birch wood were found around 180–200°C at short treatment times. This paper discusses possible degradation reactions coupled with the colour and mechanical properties in relation to acid formation, and suggestions for process optimisations. 相似文献
7.
8.
Thermal effects at the surface of a sample wood specimen while it is rubbed by reduction with a metal disk rotating at high speed are investigated. The results provide fundamental data for the development of new surface processing methods. The results of high-speed friction tests showed that the wood surface developed high-temperature regions due to the effect of friction heat, and deformed tissue was observed at the wood surface in the region that experienced the rubbing action. The thermal effects extended to a deep range in the deformed region by reduction due to different fiber inclination angles, both parallel and normal to the friction surface. The thermal effects from the rubbed conditions of the reduction and feed speed also extended deeply into the region deformed by reduction, although the thermal effect was decreased at higher feed speed. From the results of these friction tests, the change in wood temperature is described unambiguously by factors related to pressure on the friction surface. 相似文献
9.
Effects of short-term thermomechanical densification on the structure and properties of wood veneers
Pavlo Bekhta Stanisław Proszyk Tomasz Krystofiak Jan Sedliacik Igor Novak Miroslava Mamonova 《Wood material science & engineering》2017,12(1):40-54
The effects of short-term thermomechanical (STTM) densification temperature and pressure on the changes in surface roughness, wettability, mass loss (ML), thickness and density of alder, beech, birch, and pine wood veneer with low moisture content (~5%) were investigated. The anatomical structure of veneers was also observed. Veneer sheets were densified using pressure levels of 4, 8 and 12 MPa at three temperatures: 100°C, 150°C and 200°C for 4 min. The results were compared with those of the non-densified veneers. The obtained results show that STTM densification of veneers similarly to long-term densification of solid wood causes irreversible changes in their properties. The STTM-densified veneer surfaces became smoother and more hydrophobic, ML increased slightly while roughness and thickness values decreased significantly, the cell lumens collapsed and a certain amount of fractures in cell walls developed with increasing densification temperature and pressure. All of the investigated wood species showed higher density values after densification. It was found that an even STTM densification of veneers provides stable properties under normal atmosphere conditions; in particular, the thickness and contact angle values were stable for 24 hours after densification, which is an important consideration for industrial applications. 相似文献
10.
Masako Seki Hiroyuki Sugimoto Tsunehisa Miki Kozo Kanayama Yuzo Furuta 《Journal of Wood Science》2013,59(1):10-16
Friction that arises during processing for the deformation of wood under relatively high pressure levels (ca. >1 MPa) is an important factor to be taken into account when wood is processed. However, few studies on such friction have been published. The present study was undertaken to evaluate the influence of surface finishing conditions on the nominal friction coefficient (μ) of the wood and metal tool surfaces. Sticking friction was likely to arise on a relatively coarse metal surface, and the type of metal tool surface finishing was found to have large impact on the friction mechanism. The friction characteristics during exposure to high pressure seem to be affected not only by the interface contact characteristics, but also by the deformation characteristics of wood during compressive load or measurement. The value of μ on water-saturated wood was equal or higher than that on dry wood, which suggests that the contact characteristics between these two types of wood are significantly different. The water content in wood was shown to affect both the interface contact and deformation characteristics of wood. The value of μ was not significantly affected by the wood surface finishing conditions; however, changes in μ during sliding differed slightly, depending on the finishing conditions. 相似文献
11.
Pavlo Bekhta Stanisław Proszyk Tomasz Krystofiak Miroslava Mamonova Grzegorz Pinkowski Barbara Lis 《Wood material science & engineering》2014,9(4):233-245
The effect of short-term thermomechanical densification of veneer on the surface roughness and surface anatomical changes in four wood species – alder (Alnus glutinosa Gaertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) – was studied. Veneer sheets were densified at a temperature of 100, 150, or 200°C and at a pressure of 4, 8, or 12 MPa for 4 minutes. Seven roughness parameters such as Ra, Rz, Rq, Rp, Rv, Rsk, and Rku were determined. Profile surface was recorded using a modified Carl Zeiss ME-10 profile gauging profilometer. Surface anatomical changes of veneer were examined using scanning electron microscopy. The results showed that densification temperature and pressure affect surface roughness of veneer. The surface became smoother, and roughness values decreased significantly (except for Rku which increased slightly) with increasing temperature and pressure of densification. The effect of temperature on surface roughness changes is more pronounced compared with that of densification pressure. The lowest values of surface roughness were recorded for pine veneer samples followed by alder, birch, and beech samples. These results can be used to provide initial data for adhesive application processes in woodworking industry. 相似文献
12.
人工林杉木木材力学性质对高温热处理条件变化的响应 总被引：6，自引：0，他引：6
以人工林杉木为试材,分别用空气和菜子油为介质,在温度为180,200和220 ℃对其分别热处理1,3和5 h,研究试材的抗弯强度(MOR)、抗弯弹性模量(MOE)、顺纹抗压强度、表面硬度对高温热处理条件变化的响应,同时对处理材的主要化学成分进行分析,用扫描电镜对处理材横切面微观结构进行观察.结果表明:人工林杉木试材的4种主要力学性质对不同条件热处理的响应程度不同.无论是空气热处理还是油热处理,试材的MOR,MOE,顺纹抗压强度与对照比有不同程度的降低,且随处理温度升高、时间延长,下降幅度增大,相比于时间,温度的影响更显著;180 ℃热处理1,3和5 h时,试材的MOR,MOE与对照比未发生明显变化(降幅在3%以内),而顺纹抗压强度则明显低于对照,两介质中降低幅度分别在3.29%～9.58%和3.89%～7.18%;200 ℃以上处理时,不同时间处理的3种主要力学性质不仅显著或极显著低于对照,且各性质问的差异也达显著或极显著水平;对硬度的测试结果表明:180 ℃热处理时,试件的径面硬度和弦面硬度均随时间的延长而增大;200 ℃热处理3 h时,试件的硬度达最大,与对照差异达显著水平;随后热处理试件的硬度开始降低,220 ℃热处理5 h后试件的硬度又明显低于对照.在隔氧的油介质中进行热处理,4种主要力学性质的变化程度低于空气介质处理材,当温度高于200 ℃时,两介质处理间的差异达显著水平.而热处理过程中木材主要化学组成与横切面微观结构变化的差异,反映了4种主要力学性质对不同条件热处理时表现出的响应差异. 相似文献
13.
The viscoelastic thermal compression (VTC) of low-density hybrid poplar (Populus deltoides × Populus trichocarpa) from fast growing trees was performed in order to produce specimens with three different degrees of densification (63, 98, and 132%). The morphology and density profile of the VTC specimens were studied. Three different methods for the preparation of specimens for microscopy were used in order to find a technique that makes it possible to examine the VTC wood microscopically in the completely deformed state. It was found that the abrasive surface preparation of oil-embedded blocks was the most promising technique. Microscopic observation revealed that the deformations in the VTC wood were mostly the result of the viscous buckling of cell walls without fracture. The volume of the void areas in the specimens decreased with the degree of densification. The results showed that the density profile of the VTC wood varied with the degree of densification as a consequence of different temperature and moisture gradients formed before and during wood compression. The density profile is also visible on the cross-section of the VTC specimens. 相似文献
14.
The mechanical properties of 613 small clear specimens of 35 species (11 ring-porous hardwoods, 19 diffuse-porous hardwoods,
and 5 softwoods) were evaluated. The aim of the study was to examine indexes of wood quality that are easy to measure and
that exhibit a high correlation with bending performance and hardness that are essential properties of hardwood products.
The modulus of rigidity, dynamic modulus of elasticity, bending properties (modulus of elasticity, modulus of rupture, stress
at the proportional limit, absorbed energy, Tetmajer’s modulus), dynamic energy absorption by an impact bending test, compressive
strength parallel to the grain, shear strength, partial bearing strength, and Brinell’s hardness were measured. A high correlation
was found between dynamic modulus of elasticity and static modulus of elasticity. Bending stress at the proportional limit
was found to be approximately equivalent to the compressive strength parallel to the grain. Static energy absorption correlated
with dynamic energy absorption. Tetmajer’s modulus was found to be closely related to the ratio of the initial stiffness within
the elastic range to the secant modulus at the maximum load. A high correlation was observed between Brinell’s hardness and
partial bearing strength. The difference in the regression coefficients obtained for these correlations between the species
groups was small.
Part of this study was presented at the All Division 5 Conference of IUFRO, Taipei, October 2007 相似文献
15.
对3种追肥处理1(N300P200K200)、处理2(N200P100K150)和处理3(N100P50K50),从12、27、42、50、62、75、88、99、110、144到192月生的尾巨桉生长量数据进行了统计分析,并在198月生时对每种施肥处理取7株样木进行了木材的基本密度、抗弯强度、弹性模量、硬度、干缩率以及皱缩率等指标开展研究,结果如下:追肥量与生长量成正相关关系.追肥量越多,生长量越大,这种差距从追肥后就开始产生,一直到192月生时都存在;但是,这种差距在大部分时间里都未达到显著水平:达到显著差距的只有施肥处理1和处理3之间,27月生时DBH达到0.01的显著性差异、平均高在12、27和37月生时达到0.05的显著性差异、蓄积量在27、37、42和50月生时达到0.05的显著性差异.材性指标上,大径材木材材性与追肥量的关系密切,增大施肥会影响木材材性,包括降低抗弯强度,增加弹性模量,降低端、径面和弦面硬度,降低基本密度,增加木材含水率等;达到显著差异的有:木材的抗弯强度、径面硬度被显著降低,达到了0.05的显著水平.木材边材基本密度降低更大,达到了0.01的极显著水平.经过多重比较的分析,都是常规施肥处理3与处理2和常规施肥处理3与处理1两两之间差异显著.处理1和2比处理3的抗弯强度平均分别降低了12％和14％、径面硬度分别降低了11.7％和14.1％,而边材基本密度分别降低了8.6％和8.1％;因此,在培育桉树大径材时,一定要考虑合理施肥量. 相似文献
16.
以火车集装箱底板加工剩余物为原料,经过去贴面、磨砂等简单的处理后与杨木单板重组成一种层层交错结构的竹木复合建筑混凝土模板。用单因素实验方法,分析不同热压工艺参数下的静曲强度、弹性模量、含水率,从而确定热压温度、压力、时间的工艺参数范围。用正交实验法测试静曲强度、弹性模量、湿态胶合强度、密度等性能,并进行了方差分析和平均值分析。结果表明:与传统建筑混凝土模板制备方法相比,该工艺省去了去竹青、竹黄、竹节和软化等复杂的竹片材料制备方法。成品的竹材加工剩余物的体积利用率占竹木复合建筑混凝土模板的80%以上,同时节约了生产成本。通过极差分析,热压工艺因素对静曲强度、弹性模量、湿态胶合强度的影响程度都是:热压压力>热压时间>热压温度。通过平均值分析,最优热压参数为:3 MPa、50 s·mm^-1、135℃。 相似文献
17.
采用1 m3气候箱法测试2种浸渍胶膜纸饰面人造板甲醛释放规律以及不同处理条件对板材甲醛释放浓度的影响。结果表明,热压工艺、基材结构可能是影响甲醛释放周期的关键因素,2种饰面人造板的平衡周期基本相同;封边处理可有效降低甲醛含量得释放;温度和相对湿度与板材甲醛释放量呈正相关,空气交换率与板材甲醛释放量呈负相关。 相似文献
18.
19.
The objective of this study was to evaluate influence of steam treatment on surface quality and hardness of eastern redcedar (Juniperus virginiana L.). Defect-free samples with dimensions of 40 mm by 50 mm in by 20 mm were used for the tests. Specimens were exposed to steam having a temperature of 130 °C for 1-h and 3-h periods of time. Surface roughness of the samples at initial and exposed conditions was determined using stylus type equipment across the grain orientation on tangential surface of each sample. Janka hardness of the control and treated samples was also determined on Comten testing system. Based on the findings in this work, no significance was found between surface roughness values of the specimens steamed for 1 and 3 h. However, both types of steamed specimens had higher average roughness values ranging from 52 and 60 % than those of control samples. It appears that 3-h steaming adversely influenced hardness of the samples reducing its 9 % as compared to those of control samples. Densification effect of steaming on the samples was also evaluated using scanning electron microscope (SEM) and it was determined that steaming had some crushing effect on the cell wall. 相似文献
20.
Georg Behr Susanne Bollmus Antje Gellerich Holger Militz 《Wood material science & engineering》2018,13(5):262-270
Specimens of beech, ash, lime and poplar were thermally modified (T) and treated with an aqueous solution of melamine (M) resin to investigate the mechanical changes after combined (double) modification (TM). Density, solution uptake, weight percent gain, bulking and equilibrium moisture content were recorded to ensure proper treatment. Samples for Brinell hardness and three-point bending were cured at 120°C under dry conditions. The WPGs of the two treatment groups M and TM were similar, but bulking of TM specimens was negative. This might indicate an incomplete penetration into the thermally modified cell wall in combination with a potential leaching of soluble hemicellulose components by the alkaline impregnation solution. The decreased hardness of heat-treated wood was substantially increased by melamine treatment (combined modification). Both modifications and their combination slightly increased the modulus of elasticity. The modulus of rupture was increased after melamine treatment, decreased after thermal modification and combined modification. The work in bending was severely reduced for all treatments. Melamine treatment of thermally modified wood was carried out successfully and some mechanical properties were improved. Double-modified wood with increased modulus of rupture (MOR) and extraordinary surface hardness would be suitable for non-structural outdoor applications such as decking and cladding.
Abbreviations: ANOVA: Analysis of variance; EMC: Equilibrium moisture content; EMCR: Reduced (corrected) equilibrium moisture content; IB: Impact bending strength; M: Melamine treated; MOE: Modulus of elasticity; MOR: Modulus of rupture; MUF: melamine-urea-formaldehyde resin; OD: Oven dry density; R: Untreated references; RH: relative humidity; SC: Solid content; SU: Solution uptake; T: Thermally modified; TM: Thermally modified and melamine treated (double modification); WB: Work in bending; WPG: Weight percent gain 相似文献