杉木规格材圆钢钉握钉力性能研究

握钉力强度值是木结构构件连接中基本强度设计值之一.本实验采用国内市场上常见直径为2.8mm、3.1mm、3.4mm、3.6mm种普通圆钢钉,测试了国产人工林杉木规格材的握钉力强度,分析了木材密度、钉杆直径以及端纵面纹理与握钉力强度的关系,并将实验结果与北美木结构设计手册所给出了设计值计算公式相比较.实验结果表明,木材密度对握钉力强度影响最大;钉直径与握钉力呈线性正比关系.采用我国人工林杉木及市场上常用钉所连接的钉节点,握钉力强度高于北美木结构设计手册所规定的设计值,符合木结构设计规范要求,并有一定的提升空间.     

Moisture-dependent properties of barnyard millet grain and kernel

The geometric mean diameter, sphericity, grain surface area, 1000 grain mass, true density (toluene displacement method), terminal velocity, dynamic angle of repose, coefficient of internal friction, coefficient of static friction at different surfaces (sun mica, canvas and mild steel surfaces), specific deformation and rupture energy of the grain were found to increase 12.21%, 4.79%, 30.47%, 30.75%, 6.74%, 32.99%, 127.05%, 60%, 18.57%, 34–67%, 69.2% and 88.87% respectively at increase of moisture content from 0.065 to 0.265 kg kg⁻¹ dry matter. However, true density (proximate composition method), bulk density, interstices and rupture force of grain was found to be decrease 8.64%, 20.1%, 86.49% and 21.17% respectively at increase of moisture content. Similar trend was observed for barnyard kernel also. True density (toluene displacement method) was found lower as compared to true density (proximate composition method) at all experimental moisture range indicated that the presence of void space inside the grain and kernel.     

Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

In the present study, the pure viscoelastic behaviour of European beech wood is analysed in the longitudinal direction at three different moisture contents. The moisture-dependent creep compliance is identified using a four-point bending test device. The viscoelastic behaviour is ascertained to be linear with moisture content and quantified by means of a Kelvin-Voigt model approach.     

Moisture-dependent physical properties of dried pomegranate arils

Physical properties of dried pomegranate arils and its variation with moisture content play an important role in designing of equipment for storage, conveying and handling. Physical properties of dried pomegranate arils in the moisture content range of 7–28 % (d.b.) were investigated. Size (GMD), sphericity, weight of the thousand dried arils, true density, bulk density, angle of repose and coefficient of friction at different surfaces (wood, galvanized iron and aluminum) increased, whereas porosity, hardness and toughness decreased with increase in the moisture content. All physical properties except porosity and angle of repose were significantly affected by the change in moisture content at probability level p ≤ 0.01.     

Moisture-dependent engineering properties of sunflower seeds with different structural characteristics

The present study was carried out to investigate the effect of the moisture content of the seeds on engineering properties of sunflower hybrids with different structural characteristics. The properties were evaluated at seven levels of moisture from 2.0% to 20.1% (dry basis) for three selected sunflower hybrids. For both black-hull oilseed hybrid and confectionary hybrid, the variation in moisture content showed a statistically significant effect on dehulling ability, percentage of fines (broken grains with a diameter smaller than 2 mm) and all the physical properties studied (size, true density, bulk density, porosity, volume and weight, volumetric expansion coefficient, equivalent diameter and sphericity), except seed length in the confectionary hybrid and seed length and thickness in the black-hull oilseed hybrid. For the striped-hull oilseed hybrid, moisture content showed a significant effect only on dehulling ability, percentage of fines, seed width and thickness, bulk density and porosity. Of the oilseed hybrids, the striped hull genotype (higher hull content and both lower oil content and seed size) presented a higher dehulling ability. Nevertheless, the black hull hybrid resulted more sensitive to seed moisture changes. Although the confectionary hybrid showed a higher seed size, hull thickness and hull content, and lower oil content than the oilseed hybrids, the dehulling ability resulted fairly similar in the striped hull sunflower hybrids. The results suggest that sunflower seeds with different structural characteristics need to be conditioned with different moisture content before being subjected to the dehulling process.     

Improving fire retardancy of unheated and heat-treated fir wood by nano-sepiolite

European Journal of Wood and Wood Products - The effects of nano-sepiolite (NS) on fire properties of unheated and heat-treated fir wood were studied using a newly developed apparatus. Separate...     

浅析粗糙度对竹木复合板胶合性能的影响

针对粗糙度对竹木复合板胶合性能的影响进行了研究,通过对不同粗糙度表面竹材和杉木单板进行胶合,比较不同粗糙度表面对竹木复合板胶合性能的影响,研究结果表明,粗糙度对竹木复合胶合板的胶合性能影响显著.     

木材弹性模量参数的测量与发展

木材的弹性模量是衡量木材刚度特性的一个重要指标,体现了这种材料最重要、最具特征的力学性质。本文通过对木材弹性模量参数的国内外研究成果概述,以期为该领域的发展现状做出有益的探讨和总结。     

杉木木束干燥性能初探

采用热风循环试验干燥机对杉木木束进行干燥速度与能耗试验,探讨杉木木束的干燥性能.结果表明:杉木木束干燥可采用高温低湿的干燥介质进行快速干燥.为保证干燥速度,节约能耗,木束干燥前最好采用预干处理,使木束初含水率均匀;干燥介质温度应控制在140℃～160℃之间;风速控制在3m/s左右.     

Modelling mechanical properties of spruce and Douglas fir timber by means of X-ray and grain angle measurements for strength grading purpose

This study proposes a model using data from a scanner (X-ray and grain angle measurements) to perform strength grading. The research also includes global measurements of modulus of elasticity (obtained by vibrations and ultrasound methods), static bending stiffness and bending strength of 805 boards of Douglas fir and 437 boards of spruce. This model can be used in an industrial context since it requires low computational time. The results of this study show that the developed model gives better results than the global non-destructive measurements of the elastic modulus commonly used in the industry. It also shows that this improvement is particularly higher in the case of Douglas fir than for spruce. The comparison has been made on both the quality of the mechanical properties assessment and on the improvement of the grading process according to the European standards by using different index.     

Bending strength and modulus of elasticity of particleboards at various temperatures

Bending strength and modulus of elasticity of phenol-formaldehyde (PF)-bonded particleboards were studied at temperatures between -40 °C and +40 °C. These conditions may occur, for example, during exterior use of boards. Bending strength and modulus of elasticity are significantly affected by the temperature. Moreover, positive temperatures cause higher reduction of strength properties than negative temperatures. The bending strength of boards in the temperature range from -40 °C to 0 °C, for example, is reduced by 15% and in the temperature range from 0 °C to 40 °C by 28%.