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Yoshiharu Nishiyama 《Journal of Wood Science》2009,55(4):241-249
The current structural models of the cellulose microfibril as well as its mechanical and thermal properties are reviewed.
The cellulose microfibril can be considered as a single thin and long crystalline entity with highly anisotropic physical
properties. The contribution and limit of different methods employed such as electron microscopy, infrared spectroscopy, X-ray
scattering and diffraction, solid state nuclear magnetic resonance spectroscopy, and molecular modeling are also discussed. 相似文献
63.
对竹大片刨花板(BW)、木质定向刨花板(OSB)和结构胶合板(SPly)的剪切性能和以其为腹板的3种木质工字梁(IB)静曲挠度的检测和分析结果表明:腹板横截面剪切弹性模量(MOEs)与IB的静曲剪切挠度和静曲总挠度成负幂指数关系;腹板MOEs的不足对IB静曲挠度的不利影响不容忽视;实际应用中应注意到IB的跨度对静曲剪切挠度的影响;具适当MOEs的BW、OSB和SPly均可满足IB对静曲剪切挠度的要求。建议我国相关标准和规范增补或修改对腹板用木质结构板的MOEs指标要求及其检测方法,以及对IB静曲挠度中静曲剪切挠度的控制指标及其实用性工程计算方法。 相似文献
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Jun Tanabe Akira Tamura Jyunichi Ohshima Kazuya Iizuka Shinso Yokota 《Scandinavian Journal of Forest Research》2017,32(1):39-44
With emphasis on tree breeding for wood quality in Picea jezoensis, we aimed to evaluate radial and between-family variations in the microfibril angle (MFA) of the S2 layer in the latewood tracheids in 10 open-pollinated families of 43-year-old P. jezoensis trees. In addition, the relationships between MFA/wood density with the modulus of elasticity (MOE) or modulus of rupture (MOR) were investigated. Significant differences in MFA between families were found from the pith toward the bark. MFA showed higher values around the pith area, although some families showed relatively lower values than others around this area. In addition, due to a larger coefficient of variations of MFA near the pith, the potential for juvenile wood MFA improvement may be greater compared with mature wood. MOE was correlated with MFA in juvenile wood and with wood density in mature wood, whereas MOR was mainly correlated with wood density at radial positions in both woods. Therefore, to improve the MOE and MOR of P. jezoensis wood, both MFA and wood density would be factors to consider in both juvenile and mature woods. On the other hand, there are indications that, only wood density would be an important criterion for improving mature wood properties. 相似文献
65.
为提供一种更加符合蛋壳结构力学特性的测试蛋壳弹性模量的方法,以鹅蛋壳为研究对象,对鹅蛋进行轴向压缩试验,获取赤道部位的经向、纬向应变与轴向载荷之间的关系;依据旋转壳无矩理论推导出蛋壳弹性模量和泊松比的表达式,并根据试验数据求取试验鹅蛋壳的弹性模量和泊松比。测得试验鹅蛋壳弹性模量的平均值为47.33GPa,方差为5.68;泊松比平均值为0.411,方差为0.064。本研究所述测试方法更加符合蛋壳结构力学特性,可以为蛋类的生产、运输、加工装置设计提供参考。 相似文献
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Baked product texture: Correlations between instrumental and sensory characterization using Flash Profile 总被引:1,自引:0,他引:1
Fifteen wheat doughs with various compositions have been selected and baked in order to obtain products with densities in the range of commercial bread values (0.25–0.35 g/cm3). A quick sensory profiling technique (Flash Profile), based on the combination of free choice profiling and a comparative evaluation of the whole product set was used. The sensory jury had to focus on the sensory perception of crumb texture (tactile and visual). The treatment of collected data by Generalized Procustes Analysis shows that products were perceived differently by the panel. The main differences concern the uniformity and the size of gas cells but also mechanical properties of corresponding crumb for which attributes like hardness, springiness and crumbliness were used. Instrumental characterization was performed using uniaxial compression (Young's modulus) and image analysis based on texture granulometry (fineness and homogeneity of cell distribution). A Multiple Factor Analysis allowed assessing the correlations between the sensory attributes and the instrumental measurements. Density and Young's modulus are positively correlated with the sensory elasticity. The instrumental and sensory measurements of the size and of the homogeneity of the cells distribution are correlated. 相似文献
70.
It is well known that the presence of knots in structural lumber is one of the most important strengthreducing factors. For practical purposes, visual grading including knot restriction is an effective method for nondestructive evaluation of strength. Edge knot restriction for not only visually graded lumbers but also mechanically graded lumbers is specified in the Japanese agricultural standards for glued laminated lumber. We conducted experimental studies on differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch (Larix kaempferi, carriere) lumbers daily used for manufacturing glued laminated timbers in Nagano, Japan. We then examined the additional visual grading of mechanically graded lumbers for nondestructive evaluation. We visually graded the prepared mechanically graded lumber by focusing on the knots' area ratio of grouped knots. We confirmed that the higher visual grade related to the stronger tensile strength, similar to our present knowledge; but the effects of knot restriction were reduced when the length of the lumber increased in view of nonparametric 5th percentiles of tensile strength. The differences in the strength/elasticity ratio between mechanically high-grade and low-grade lumber were negligible. It was clear that the length effect on the ratio in visually graded high-grade lumber was smaller than that of visually graded low-grade lumber. It was thus concluded that knot restriction should have little effect on the tensile strength of mechanically graded lumber. 相似文献