共查询到20条相似文献，搜索用时 31 毫秒
1.
《Wood material science & engineering》2013,8(4):219-227
Abstract Heat treatment of wood is an effective method by which to improve the dimensional stability and biological durability, but the mechanical strength is decreased at the same time. Besides chemical modification of cell-wall constituents, physical weakening of the microstructure owing to heat-induced defects may also contribute to strength loss. Therefore, anatomical properties of heat-treated beech (Fagus sylvatica L.) and spruce (Picea abies Karst.), studied by light microscopic and scanning electron microscopic analysis, and their interrelation with strength properties and structural integrity were investigated. For determination of structural integrity, the high-energy–multiple-impact (HEMI) test was applied. Microscopic analyses showed frequent formation of radial cracks in heat-treated beech close to the rays as well as tangential cracks in the latewood of spruce. In addition, the modulus of rupture was more affected by the heat treatments than the resistance to impact milling (RIM) determined by the HEMI test, because RIM is based on multiple fractures on the microlevel that are not affected by the formation of intercellular cracks or other defects due to the heat treatment. It was concluded that heat-induced defects in the wood microstructure contribute to the substantial strength loss of thermally modified timber. 相似文献
2.
《Wood material science & engineering》2013,8(1):13-23
Abstract Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself. 相似文献
3.
Bruna Ugulino 《Wood material science & engineering》2018,13(2):64-72
Sanding is the most common machining process used to prepare wood surfaces prior to coating. Hence, to improve surface quality and coating performance during this process, an optimal set of machining parameters should be established according to wood species and its final use. The effects of grit size and feed speed on surface properties and coating performance of red oak wood were studied. Surface quality was assessed by surface roughness, scanning electron micrographs, and wetting analyses. Coating performance was evaluated using pull-off adhesion tests on coated surfaces before and after an accelerated weathering. The results showed that smoother surfaces are obtained as the grit size number of the abrasive increased. On the other hand, minor differences were observed on cell damages and surface roughness as feed speed changed. Also, there was little difference among treatments concerning wetting behavior and surface energy. Pull-off strength was more affected by changes in grit size than feed speed. A P100-grit size program with a feed speed of 7 m/min resulted in a suitable roughness which provided good adhesion and high pull-off strength after aging test. 相似文献
4.
采用挤出成型制备了竹粉增强聚丙烯复合材料,研究竹粉/聚丙烯复合材料在紫外加速老化与湿热老化后的力学性能变化与尺寸稳定性.结果表明:在紫外线加速老化200 h后,复合材料的弯曲强度与弯曲模量无显著变化,试件宽度与厚度在紫外加速老化前后也无显著改变;但湿热老化对复合材料的弯曲强度与弯曲模量有显著影响,在沸水中浸泡2h后,复... 相似文献
5.
Eylem Dizman Tomak Elif Topaloglu Nurgul Ay Umit C. Yildiz 《Wood Science and Technology》2012,46(5):905-918
The objective of this study was to investigate the effect of accelerated aging on compression strength, modulus of rupture, modulus of elasticity, color change, volumetric swelling, and volumetric shrinkage of bamboo specimens with and without node sections. In the study, these properties were compared with those of Scots pine and beech wood specimens. Depending on bamboo sections, the aging procedure reduced modulus of rupture, modulus of elasticity, and compression strength. Bamboo specimens showed relatively high strength properties compared to wood specimens due to having high density. Strength properties increased from bottom to top of bamboo culms. The presence of nodes in the specimens reduced compression strength and modulus of rupture but affected modulus of elasticity slightly. Remarkable color changes in specimens were observed after aging. Volumetric swelling and shrinkage of bamboo specimens exposed to aging decreased probably due to heat effect of aging procedure. 相似文献
6.
采用加速老化试验方法对竹复合管材的湿热老化性能及老化机理进行研究,探究不同湿热老化历时下竹复合管材拉伸、压缩和弯曲性能的变化。结果表明,在交变湿热应力作用下,竹复合管材拉伸强度、压缩强度、压缩弹性模量、弯曲强度和弯曲弹性模量随湿热老化时间延长呈幂指数降低,拉伸劣化大于弯曲,弯曲劣化大于压缩,模量劣化大于强度;湿热老化28次后,竹复合管材拉伸强度、压缩强度、压缩弹性模量、弯曲强度和弯曲弹性模量分别降低34.11%、25.64%、26.39%、26.14%和27.83%。交变湿热应力使结构层树脂和竹纤维均发生湿胀,结构层树脂湿胀率小于竹纤维,不均匀的湿胀使结构层树脂受拉、竹纤维受压,结构层树脂竹纤维界面产生剪切力,树脂开裂、脱落,纤维树脂界面形成孔洞和微裂纹降低有效应力传递,当剪切力大于界面粘结力时,界面损伤模式主要表现为脱粘以及剪切分层。 相似文献
7.
在100℃、50%相对湿度的无光条件下,对虫胶涂层和基材进行288 h的老化试验,采用扫描仪、积分球式分光度谱仪、傅里叶红外光测谱仪检测其老化过程中物理和化学变化,从表面颜色、附着力和耐冷液体性能三方面研究高温老化对涂层质量的影响。结果表明:高温老化后,虫胶涂层颜色变深,附着力下降,但耐冷液体性能有所提高。红外光谱表明:虫胶中部分游离羟基发生内脂化反应导致涂层性能变化;基材颜色加深,红外光谱中3400 cm-1和1645 cm-1两处峰强有微弱变化,说明高温环境下半纤维素有部分降解。涂层颜色的变化是由涂料和基材颜色变化叠加的结果。 相似文献
8.
论述和分析木质剩余物复合材料老化的原因,主要有木质剩余物的老化、胶粘剂的老化、木质剩余物的回弹和膨胀—收缩应力。综合论述木质剩余物复合材料加速老化试验方法,指出木质剩余物复合材料在加速老化试验方面的研究,适宜采用ASTM D1037六循环加速老化法和老化仪检侧法。分析木质剩余物复合材料老化的影响因素,如温度、湿度、试件尺寸等。 相似文献
9.
Since the structure of oil palm wood varies dramatically, the property gradients of oil palm wood within a trunk are of great interest. In this study, the physical (density, water uptake and swelling in the radial direction) and mechanical properties (bending modulus of elasticity and strength, compressive modulus of elasticity and strength in the direction parallel to the fiber, compressive strength in the direction perpendicular to the fiber and shear strength in the direction parallel to the fiber) of oil palm wood for a whole trunk were examined. The water uptake, compressive strength in the direction perpendicular to the fiber, shear strength in the direction parallel to the fiber, bending modulus of elasticity and strength and compressive modulus of elasticity and strength in the direction parallel to the fiber appeared to be independent of trunk height but tended to be related to the relative distance from surface or density by a single master curve. However, the swelling in the radial direction of the oil palm wood was not correlated with the relative distance from the surface, trunk height or density. Finally, property map of oil palm wood for a cross section at any height was prepared for practical use. 相似文献
10.
《Scandinavian Journal of Forest Research》2012,27(2):237-246
Rate of growth and wood properties of Sitka spruce (Picea sitchensis (Bong.) Carr.) were investigated in triplet mixtures with lodgepole pine (Pinus contorta Loud.) (Alaskan provenance) and Japanese larch (Larix kaempferi (Lamb.) Carr.), established on nitrogen-deficient, iron pan soils. These ?nursing? mixtures were compared with pure stands of Sitka spruce that had been either regularly or periodically fertilized with nitrogen. Japanese larch promoted a growth rate in Sitka spruce greater than that achieved in the lodgepole pine-nursed spruce and equivalent to the two pure spruce treatments over the duration of the experiment (current age 28 yrs). Growth of regularly fertilized pure Sitka spruce was not significantly greater than that of periodically fertilized pure spruce. Alaskan lodgepole pine controlled branch size on the lower part of the spruce stems more effectively than the other treatments, although this may have been a function of tree size. Branch characteristics of Japanese larch-nursed spruce, however, were similar to those of the pure spruce treatments. Japanese larch caused an imbalance in crown development in the spruce, although it is unclear from the present study whether this will have an influence on stem and wood quality by the end of the rotation. Overall, the evidence from this study suggests that Japanese larch is an effective nurse of Sitka spruce on nitrogen-deficient iron pans, maintaining a rate of growth similar to that of pure Sitka spruce periodically fertilized with nitrogen and higher than that observed in spruce nursed by Alaskan lodgepole pine. 相似文献
11.
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
12.
《Wood material science & engineering》2013,8(1):64-88
Abstract This state-of-the-art report presents the basic concepts of some of the thermo-hydro (TH) and thermo-hydro-mechanical (THM) wood processes that are in use today, i.e. heat treatment, compression of wood in the longitudinal or transverse direction and wood welding. The reasons for the growing interest in TH and THM techniques are discussed, and the development of the different concepts, from first ideas to current status, is briefly presented. The physical and chemical changes that occur in wood during TH and THM processing according to the latest research are also presented. Finally, developments that are close to or already have an industrial application are presented, and the challenges for further development of the heat treatment, compression and wood welding processes are discussed. The TH processing of wood is based entirely on water and heat, and a THM process incorporates an additional mechanical force. The purpose of wood transformation by a TH or a THM process is to improve the intrinsic wood properties, to acquire a form and functionality desired by engineers without changing its eco-friendly characteristics or hindering its further use in the total material life cycle. Only a few of the recently developed techniques, e.g. heat treatment, wood welding and various densification applications, have been industrialized to some extent. There are many reasons for this relatively low transfer of the research results to a full up-scaled industrial production. Some of them are related to unsolved problems at the laboratory level on small-sized samples and others are related to the scaling-up processes in industry. Furthermore, the ageing of heated wood leads to deterioration with time, in some cases there is an unpleasant odour, the strength of the wood decreases substantially and the wood becomes more brittle. These are new challenges which need to be resolved by the collaboration of researchers from the different scientific domains of academia, research institutes and industry. 相似文献
13.
Maria Christiernin Shannon M. Notley Liming Zhang Thomas Nilsson Gunnar Henriksson 《Wood Science and Technology》2009,43(1-2):23-41
Wood from white spruce Picea glauca that had been preserved by rapid burial in lake sediments 10,000 years ago, was investigated and compared to a contemporary reference white spruce wood. The 10,000-year old sample appeared to have an intact primary cell wall and middle lamella, whereas the carbohydrate monomer distribution, and microscopic images showed that the secondary wall was at least partially removed, indicating that this structure had been selectively attacked by bacteria. The Klason lignin amount in the aged spruce was found to be 60%. The relative lignin monomer content in the aged spruce was 9% lower than that of the reference wood, showing that there were fewer β-O-4′ linkages in the aged sample. This finding was supported by SEC analysis of the thioacidolysed samples as a larger proportion of lignin oligomers were observed in the aged spruce than in the reference material. This indicates a somewhat greater number of condensed bonds in the aged spruce than in the reference spruce sample. Quantitative 13C NMR analysis and HSQC techniques applied on milled wood lignins (MWL) revealed no significant structural differences between the aged spruce and the reference. 相似文献
14.
We examined the applicability of the Iosipescu shear test for measuring the shear properties of wood. Quarter-sawn board of sitka spruce (Picea sitchensis Carr.) and shioji (Japanese ash,Fraxinus spaethiana Lingelsh. were used for the specimens. Iosipescu shear tests were conducted with two types of specimen whose longitudinal and radial directions coincided with the loading direction. The shear modulus, yield shear stress, and shear strength were obtained and were compared with those obtained by the torsion tests of rectangular bars. The results are summarized as follows: (1) The Iosipescu shear test is effective in measuring the shear modulus and the yield shear stress. (2) To measure the shear strength properly by the Iosipescu shear test, the configuration of specimen and the supporting condition should be examined in more in detail. 相似文献
15.
《Wood material science & engineering》2013,8(4):186-195
Abstract This work was an investigation of the effect of nanoparticles on the durability of wood specimens exposed to artificial weathering. TiO2 and clay nanoparticles were mixed with preservative (Wolmanit CX-8) for improving the durability of Norway spruce (Picea abies). Impregnated and untreated specimens were subjected to Atlas Solar Simulator accelerated ageing test chamber for solar radiation and water spray exposure. The effectiveness of the treatment against colour and chemical changes was investigated using CIEL*a*b* colour measurements system and Fourier transform infrared analysis. The present study showed that the wood specimens that had been treated with preservatives containing nanoparticles were slightly more stable against artificial ageing than both untreated specimens and specimens treated with preservative alone. 相似文献
16.
The dormancy and vigor of Picea abies seeds were studied after five months of storage at 25 and 75% relative humidity (RH) and 5 and 12 °C. Dormancy was evaluated by studying germination response to light and moist chilling at 12 and 21 °C. Dormancy causing germination reduction in the dark was induced in seeds during storage at 25% RH (5–6% moisture content, MC) in darkness. The dormancy was greater when seeds were germinated at 12 than at 21 °C and after storage at 12 than at 5 °C. The effective dormancy relief by light indicates that germination was under phytochrome control. Moist chilling could partly replace light. According to accelerated aging and leachate conductivity tests, dry seeds could be stored at 12 °C for five months without affecting their vigor. After storage at 75% RH (11% MC) and 5 °C, the seeds germinated slowly and incompletely. The decreased germination response to light indicates that other processes than those mediated directly by phytochrome restricted germination of these seeds. The positive germination response to moist chilling suggested that secondary dormancy was induced in the seeds. However, vigor tests gave some evidence of simultaneous decrease of vigor. Storage at 75% RH and 12 °C decreased germination nearly to 0%. Germination of seeds stored at 75% RH could be stimulated by a short accelerated aging period. 相似文献
17.
18.
Surface quality and gluing performance of black spruce samples prepared by peripheral straight-edge knife planing and sanding were studied. Four wavelengths (1.5, 1.9, 3.1, and 6.5 mm) and four rake angles (15°, 20°, 25°, and 30°) were tested for peripheral planing. Three feed speeds (4, 10.5, and 17 m/min) and three grit size sandpapers (80, 100, and 120) were studied for sanding. The resulting surfaces were glued with an isocyanate adhesive and tested to evaluate their gluing performance (shear strength and percent wood failure). Results revealed that planing with a rake angle of 20° and wavelengths of up to 3.1 mm produced wood surfaces with adequate glueline shear strength. Sanding with 80-grit sandpaper produced the best glueline shear strength, regardless of feed speed. After accelerated aging, the loss of gluing performance was lower for the sanded samples compared with that of planed samples. In general, sanding process produced better wood surfaces for bonding with the adhesive studied. 相似文献
19.
B. A.. -L. Östman 《Wood Science and Technology》1985,19(2):103-116
Summary The immediate tensile strength parameters for spruce parallel to the grain and for hardboard have been determined at equilibrium conditions at temperatures up to 250°C. Below 100°C the moisture content has been varied between 0 and 30%. Above 100°C dry samples have been studied. An increase in moisture content up to about 12% leads to a slight increase in the tensile strength of spruce whereas the modulus of elasticity remains constant. With a further increase in moisture content, both properties decrease significantly. At any given moisture content, both properties decrease with increasing temperature. The corresponding strain at rupture is constant. An increase in temperature leads to a more or less linear decrease in the tensile strength and in the modulus of elasticity up to about 200°C. Above 200°C there is a more rapid decrease due to thermal softening. It is most relevant to consider the relative strength decrease since the absolute levels may be quite high due to the fact that wood samples without any irregularities were used. Such relative strength data are compared with the small amount of similar data found in the literature. The effects on the modulus of elasticity are discussed in terms of thermal softening and of water as a softener for the cellulose/hemicellulose polymers. The glass transition temperature is determined as a function of the moisture content.A special thank to Ms. K. Bojadzijev for skillful experimental assistance, to Prof. E. L. Back for stimulating discussions and to the fund for research in woodworking industries for financial support 相似文献
20.
《Forest Ecology and Management》1998,112(3):203-211
Genetic control of germination parameters and the effects of accelerated aging in mountain hemlock (Tsuga mertensiana [Bong.] Carr.) seeds were investigated using standard germination tests and simulated aging, respectively. Germination parameters were studied on seeds collected from individual trees from two natural populations (Sooke and San Juan) located on southern Vancouver Island, BC. Strong genetic control was confirmed by the high heritability estimates that ranged from 0.35 to 0.82 (stratified) and from 0.58 to 0.73 (unstratified) for Sooke and from 0.30 to 0.85 (stratified) and from 0.45 to 0.84 (unstratified) for San Juan. Simulated aging was conducted on eight seedlots collected from natural stands representing the species distribution in British Columbia. Stratified and unstratified seeds were aged at 100% RH and 37.5°C for 0 to 21 days at 3-day intervals. Seed aging accounted for the majority of variation which ranged from 97.61% to 99.86% of the total variation observed. Gradual loss of seed viability was observed over the aging treatments with a total loss of viability after aging for 12 days. Differential losses in viability among seedlots were maximum after aging for 6 days. Results are discussed in terms of the impact of long-term storage and the reliance on seed banks for ex-situ conservation of this species. 相似文献