毛竹不同种源竹材物理力学性质初步研究

通过对来自福建建瓯试验地16个毛竹种源竹材的密度、顺纹抗压强度、顺纹抗剪强度、顺纹抗拉强度和弦向抗弯强度及其弹性模量等物理力学性质的初步研究,结果表明:竹材物理力学性质在各种源之间存在一定的差异,其中湖南株洲的毛竹竹材物理力学性质比于其它种源的毛竹要好,而安徽霍山的毛竹竹材的物理力学性质较差,测量的各指标中有基本密度、抗剪强度、抗拉强度三项指标都达到最低;竹材密度的大小、抗拉强度的高低随种源纬度的降低而呈降低的趋势,而竹材的抗剪强度呈与之相反的趋势。     

藤家具用单叶省藤藤条顺纹抗拉性能比较

沿单叶省藤径向由外而内选取5种常用的编织条,进行顺纹拉伸试验及性能比较分析,考察不同径向取材位置对顺纹抗拉性能的影响.结果表明,径向取材位置对藤条的顺纹抗拉强度和弹性模量均具有显著影响.顺纹抗拉强度平均值由大到小依次为:二层扁平藤皮＞半圆藤芯＞圆藤芯＞头层扁平藤皮＞扁平藤芯;拉伸弹性模量平均值由大到小依次为:圆藤芯＞半圆藤芯＞二层扁平藤皮＞扁平藤芯＞头层扁平藤皮.径向取材位置由外而内对应的藤条顺纹抗拉强度和弹性模量值均呈现先增加后减小的趋势.     

气干和饱水状态下毛竹4种力学性质的比较

以毛竹为研究对象,测试不同年龄毛竹顺纹抗剪强度、顺纹抗压强度、弯曲模量和顺纹拉伸弹性模量在气干状态(北京,含水率8%)和饱水状态下之间的差异,由此探索竹材力学性能的含水率依赖特性.结果表明:上述4种力学性能指标对含水率变化的敏感程度不同,顺纹抗剪强度和顺纹抗压强度受含水率的影响程度最大,弯曲模量次之,顺纹拉伸弹性模量最小;4种力学性能指标对含水率变化的敏感程度均随着竹龄的增大而降低,但是受影响的程度不同,其中顺纹抗压强度从气干到饱水态的降幅受竹龄的影响最小,最大和最小降幅之间的差值只有3.6%,顺纹剪切强度和顺纹拉伸模量次之,弯曲模量最大,差值为14.77%.     

基于数字散斑相关方法的竹材变形特性

利用数字散斑相关方法(DSCM)测定5个竹龄的竹材顺纹抗拉弹性模量,并实时拍摄竹材拉伸和压缩过程中的位移变化,得出竹材抗拉和抗压试样的应变场。结果表明:从竹青至竹黄,顺纹抗拉弹性模量大致呈减小的趋势;随着竹龄的增大,顺纹抗拉弹性模量逐渐增加。竹材破坏过程复杂且能够直观地反映破坏的全过程,与人们肉眼观察相比,DSCM可提前反映试样状态并预见试样的破坏点。     

大木竹竹材力学性质的研究

在浙江平阳竹木混交林内,采集3年生大木竹,按标准制成试样,测定了丛生竹种大木竹竹材的各力学性质,并以材性优良的毛竹为参比进行分析.结果发现:大木竹竹材的顺纹抗拉、顺纹抗压、抗劈力和抗弯弹性模量分别为238.0 MPa、75.1 MPa、45.6 N·mm-1和12.6 GPa,比毛竹材的相应值大或与毛竹相当,顺纹抗剪和抗弯强度较毛竹材为低.大木竹的各力学性质间有较密切的相关性,顺拉强度:顺压强度:顺剪强度:抗劈力:抗弯强度为3.2:1.0:0.2:0.6:1.8.该研究结果可为大木竹的合理开发利用提供理论依据.     

竹材顺纹抗拉强度试件数控加工工艺及技术

竹材顺纹抗拉强度是竹材重要的力学性能指标之一。手工加工竹材顺纹抗拉试件不能保证其尺寸精度,严重影响测试数据的科学性和准确性。本研究探索了该试件关键尺寸一次定位数控加工工艺及技术,提出了一个高效、快速、精准加工竹材顺纹抗拉试件的数控加工方法。     

安徽霍山不同海拔毛竹材力学性质分析

安徽霍山县靠近毛竹天然分布的北部边缘,其独特的地理位置及气候条件影响着毛竹材的各项特性,其中海拔是影响毛竹材力学性质的重要因子。以安徽霍山不同海拔（设120、230、370、510和600 m 5种海拔处理）的毛竹材为试验材料,研究了海拔因子对竹材力学性质的影响。结果表明：海拔因子对霍山毛竹的竹材密度有一定影响,随海拔升高,竹材的气干密度和全干密度呈增大趋势,但差异不大;海拔因子对竹材的顺纹抗压强度和顺纹抗剪强度有显著影响,但对顺纹抗拉强度影响不大。霍山毛竹材的各项力学特性接近传统的建筑用木材,经过合理加工可以替代传统木质建筑材料。     

样品尺寸对竹材顺纹压缩力学性能的影响研究

以毛竹为研究对象,通过对不同尺寸的样品进行顺纹压缩测试,分析样品尺寸对竹材顺纹压缩模量和顺纹抗压强度的影响。结果显示：竹材的顺纹压缩模量与竹壁厚度、样品高度、弧度呈正相关关系,顺纹抗压强度与竹壁厚度、样品高度、弧度呈负相关关系。在弹性变形阶段,样品尺寸的增加会提高维管束的组织比量而增大竹材顺纹压缩模量的计算值,在塑性变形阶段,样品尺寸和弧度会导致提前失稳而降低竹材的顺纹抗压强度。     

测试方法对毛竹顺纹抗剪强度的影响

以4年生毛竹为对象,分别按照国家标准、行业标准和国际标准的方法,进行顺纹抗剪强度的测试.结果表明:测试方法、试件形状以及加载速度对抗剪强度均有显著影响;行业标准的试件形状能较准确测出竹材的纯抗剪强度,综合测试时间,加载速度以0.8～1.5 mm/min为宜.     

不同竹龄、部位竹材经软化后的力学性能比较研究

以毛竹为研究对象,对3个竹龄(1.5、3.5和5.5年生)和5个纵向高度段竹材进行水煮软化处理,比较研究水煮软化后不同年份,不同部位竹材顺纹抗拉强度,顺纹抗压强度,静曲强度和抗弯弹性模量的变化情况,以了解其变化规律。结果表明:1在水煮软化循环实验处理下,毛竹的顺纹抗压强度、顺纹抗拉强度,抗弯弹性模量均呈现下降趋势;2从竹龄来看,在水煮软化循环作用下,5.5年生的毛竹材的各项性能变化差异最小,性能较稳定;1.5年生的毛竹材的性能变化差异最大,较不稳定。3从5个纵向高度看,毛竹材自下而上的顺纹抗压强度、顺纹抗拉强度的变化差异逐渐减小,即毛竹的基部的性能的变化最大,较不稳定,梢部的性能变化最小,较稳定。     

Variation in tensile properties and relationship between tensile properties and air-dried density for moso bamboo

This research investigated the variation in tensile properties and the relationship between the tensile properties and the air-dried density for the moso bamboo (Phyllostachys pubescens) by sampling at different heights and radial positions. Results showed that the variation of the longitudinal tensile properties in the radial direction was greater than that in the longitudinal direction. The longitudinal tensile modules of elasticity (MOE) ranged from 8.49 to 32.49 GPa. MOE for the outermost layer was 3–4 times as high as that for the innermost layer. The longitudinal tensile strength (MOR) ranged from 115.94 to 328.15 MPa. MOR for the outermost layer is 2–3 times as high as that for the innermost layer. Linear and curvilinear regressions were done from tested data of MOE, MOR and air-dried density in this paper. The linear equation worked a little better than the curvilinear one to predict the longitudinal MOR and MOE from air-dried density. __________ Translated from Scientia Silvae Sinicae, 2006, 42(3): 72–76 [译自: 林业科学]     

毛竹维管束的拉伸性能研究

采用机械剥离的方法制取竹材不同部位的维管束,并用激光共聚焦显微镜确定维管束的组成与面积,使用微型万能力学试验机测试维管束的拉伸强度和模量。试验结果表明,沿竹材径向内层到外层,维管束的强度和模量不同,拉伸强度在290～950MPa之间,模量在19～55GPa之间。     

Property gradients in oil palm trunk (<Emphasis Type="Italic">Elaeis guineensis</Emphasis>)

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.     

人工林杉木和杨树木材物理力学性质的株内变异研究

按照中国国家标准研究杉木和I-214杨树木材的抗弯弹性模量、抗弯强度、顺纹抗压强度和密度,同时按照日本国家标准研究2个树种的顺纹抗剪强度.结果表明:杉木的抗弯强度、顺纹抗压强度和密度由胸高直径处向上呈波浪形增加,抗弯弹性模量则稳定降低,但不同高度间杉木的物理力学性质没有显著差异;近树皮处木材的物理力学性质高于近髓心处木材,并有极显著差异.对于I-214杨树,只有抗弯弹性模量从髓心到树皮逐渐增加,其他的物理力学性质,最小值在从髓心到树皮的过渡区,最大值在近树皮处,从髓心到树皮,杨树的物理力学性质有极显著的差异.杉木和杨树的径面顺纹抗剪强度从髓心到树皮有极显著差异,并且近树皮的高于近髓心的木材,而弦面顺纹抗剪强度从髓心到树皮没有显著差异.木材密度与力学性质有很好的线性相关关系,木材密度是一个很好的力学强度的预测手段.     

毛竹筒展平板微观结构和基本性能初步研究张

为了拓展竹展平板后续加工应用,对毛竹筒高温软化前后及展平板的显微构造及基本力学性能进行了观测与测试。结果表明:竹材软化后的薄壁细胞变形较小,展平后的薄壁细胞变形较大。对比原竹材与展平板的物理力学性能,展平板的密度和抗弯弹性模量分别比原竹材增大4.40%和6.76%,静曲强度、顺纹抗压强度和顺纹抗拉强度分别降低4.35%、4.32%和20.52%。除顺纹抗拉强度指标外,其他物理力学性能指标在展平前后变化不大,基本不影响其后续的加工利用。     

赛黑桦的构造特征和物理力学性质

赛黑桦(Betula schmidtii),又称辽东桦,散孔材;木质厚重、坚硬,传统上用来制作车轴、木锤、擀面杖、算盘珠等(戚继忠等,2009;Akcehob et al.,2006),主要生长在我国东北东部与朝鲜接壤地区,与该地区相邻的朝鲜南部和俄罗斯南部海滨一带(锡霍特山脉南端)亦有分布,成年立木高约20m,树干直径约70cm,寿命约300～350年(Nechaeva,1972;Red     

Effects of density and anatomical feature on mechanical properties of various wood species in lateral tension

This study is focused on what factor mainly affects the mechanical properties of each wood species in the lateral direction. At first, the influence of the density which is closely related to mechanical properties in the longitudinal direction was also researched in the lateral direction. Thus, the elastic modulus, strength, and failure strain in the lateral tension were measured using thin cross-sectional samples of softwoods and hardwoods, having wide varieties in the density and anatomical features. The results obtained are as follows. The linear relationship between the density and the elastic modulus which has been verified in the longitudinal direction was not observed in the lateral tension for the samples with the annual ring inclination of 90°, which samples were influenced by ray arranged parallel to the tensile direction. However, samples with the annual ring inclination of 45° showed the high correlation between the density and the elastic modulus due to the shearing deformation of the cell shape. On the other hand, the proportional relationship between the elastic modulus and strength which has been verified in the longitudinal direction was not observed in the lateral tension except for the samples with the annual ring inclination of 90°. From the results obtained, it was revealed that the mechanical properties of wood in the lateral direction were significantly affected not only by the density but also by the structural features such as deformation of cell shapes, arrangement of ray or vessels, and the degree of the transition from the earlywood to the latewood.     

Spatial correlation of tensile perpendicular to grain properties in Norway spruce timber

Tensile strength perpendicular to grain constitutes one of the most vulnerable properties of timber. Due to versatile influencing parameters this property exhibits a high amount of uncertainty. Thus, progress in modeling, in particular by considering stochastics, is seen as worthwhile. This increases the reliability estimates of timber constructions but also their economic efficiency. Test data of tensile properties determined on consecutive board segments of Norway spruce are analyzed. The data consists of four subgroups, classified in regard to segment length and radial position within the log. The correlation in longitudinal direction of perpendicular to grain tensile strength and elastic modulus as well as of density is examined. This is done depending on the radial position of structural timber within the log. A second-order hierarchical model together with equicorrelation is used. The results outline the applicability of the model and allow the quantification of equicorrelation coefficients of all three properties. The outcome provides a valuable and necessary input for state-of-the-art mechanics-stochastic modeling of the resistance perpendicular to grain tensile strength and elastic modulus of unjointed and jointed structural timber, but in particular of products available in large dimensions, like glued and cross-laminated timber. Additionally, the spatial correlation of density is discussed which is seen as worthwhile for the estimation of group action of fasteners. The necessity to differentiate between the variability within and between segments of structural timber is clearly demonstrated.     

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.     

疏解次数对竹基纤维复合材料性能的影响

以慈竹为试材,探讨疏解次数对竹基纤维复合材料性能的影响.结果表明:随着疏解次数的增加,板材的静曲强度亦逐渐增加,弹性模量呈先增后降的趋势,抗压强度提升,抗拉强度降低,耐水性能增强.建议:当要求较高的抗拉强度时,以疏解3次最佳;要求较高的抗弯、抗压强度和耐水性能时,以疏解7次为宜.