竹材径向动态力学性能研究

采用动态热机械分析仪研究了竹材不同部位制得的径向竹篾的动态热力学性能。结果表明:测试频率对竹材径向的动态热力学性能影响较小;竹材不同部位制得的径向竹篾的储能模量(E′)均随着试验温度的升高而逐渐降低,损耗模量(E″)和损耗角正切都随着试验温度的升高而逐渐上升;三种径向竹篾的玻璃化转变温度值非常接近,储能模量的大小顺序为:基部径向竹篾中部径向竹篾梢部径向竹篾;在径向竹帘胶合的生产中增大梢部径向竹篾的使用量,有利于提高其耐温能力。     

密闭高温软化处理竹材的玻璃化转变温度

动态热机械分析(DMA)可以用来评判水热处理竹材的效果.DMA研究表明:高温软化处理的竹材,其储能模量明显降低,在40℃时,经高温软化处理后竹材的储能模量比未软化处理后的竹材降低了60.4%;未软化处理竹材的玻璃化转变温度(Tg)为119.8℃,软化处理竹材的玻璃化转变温度(Tg)为88.4℃,软化处理竹材的Tg比未软化处理竹材的Tg下降了26.2%.     

氨水与不同浓度尿素联合处理对竹材软化效果的影响

采用6%浓度氨水浸泡后与10%、20%、30%、40%、50%浓度尿素溶液蒸煮(95℃)的方法对有竹节和无竹节毛竹(Phyllostachys heterocycla cv.pubescens)材进行软化处理,展平试验及XRD和FTIR分析,结果表明:竹材的展平裂缝数均随着尿素浓度的增加而减少,当尿素浓度较低时,竹节的有无对裂缝数的影响不大,当尿素浓度较高时,无节竹材展平裂缝数明显小于有节竹材的裂缝数;竹筒曲率半径随着尿素溶液浓度的增大而增大,当尿素浓度较低时,有无竹节对竹材曲率半径变化率的影响不大,当尿素浓度在较高时,无节竹材的曲率半径变化率明显高于有节试件的曲率半径变化率;XRD分析表明,试件相对结晶度随尿素浓度增加而增大的原因是由于试件蒸煮处理的过程中试件中的抽出物的溶出,非结晶区内纤维素微纤丝的表面活性得到表现。另外在蒸煮过程中木质素的玻璃化转变温度降低,导致木质素部分降解;FTIR分析结果表明,随尿素浓度增加竹材表面羟基(-OH)数量显著增加,结晶度逐渐增大,最高时可达59.91%,竹材表面裂缝数逐渐减少。     

竹龄与竹材部位对毛竹材动态黏弹性的影响

以毛竹材为研究对象,探索不同竹龄、竹秆部位、竹壁部位对毛竹材动态黏弹性的影响。结果表明：在相同的测量条件下,随着测试温度的升高,毛竹材的贮存模量逐渐减小,损耗模量先增大后减小。随着竹龄的增加,毛竹材的贮存模量和损耗模量逐渐增大;在竹秆轴向上,毛竹材的贮存模量和损耗模量自下而上逐渐增大;在竹壁径向上,毛竹材的贮存模量和损耗模量由内而外逐渐增大。     

毛竹动态粘弹性研究

采用动态力学分析仪(DMA)和傅立叶变换红外光谱(FTIR)对取自竹青和竹黄两部分试件的动态力学性能变化规律和化学结构进行研究,结果表明:随着测试温度的升高,取自竹青部位和竹黄部位试材的贮存模量都有降低趋势,但在相同的测量方式下取自竹青部分试件的储存模量和损耗模量皆大于取自竹黄部分的试件,在温度超过160℃后,各试材的损耗角正切值都急剧增加;红外吸收光谱图发现取自竹青部分试件的羟基吸收峰强度和羰基吸收峰的强度都明显低于取自竹黄部分的试件。     

蔗渣纤维增强聚丙烯复合材料的力学性能研究

利用甘蔗渣纤维作为增强剂,回收的聚丙烯塑料作为基体,并添加MAPP为偶联剂,通过熔融混合、注射成型法制成蔗渣纤维/PP 复合材料,研究蔗渣纤维和偶联剂对复合材料静态及动态力学性能的影响。结果表明：与PP相比,添加了蔗渣纤维和MAPP后,除抗拉强度外,复合材料的静态力学强度有所提高;复合材料的储能模量和损耗模量增加,而损耗因子降低;蔗渣纤维/PP复合材料的玻璃化转变温度Tg为61.8℃。     

白蜡树杆材的剖面密度及与动态力学性能的关系

以6年生白蜡树（Fraxinus chinensis）杆材为试材，利用剖面密度仪测试其不同高度的剖面密度，并分析白蜡树杆材不同高度剖面密度与动态力学性能的关系。结果表明：白蜡树杆材近树皮的木材密度最低、由树皮到近髓心部位的木材密度逐渐升高、髓心处的木材密度又较低；下部的密度平均值为409.0 kg/m3、中部的密度平均值为313.3 kg/m3、上部的密度平均值为304.1 kg/m3；下部心材密度值较集中，而中部和上部心材密度值波动性较大；除白蜡树杆材上部剖面密度与储能模量不显著相关外，白蜡树杆材其他部位的剖面密度与储能模量、损耗模量和损耗因子等动态力学性能极显著相关。     

毛竹节间材与节部材的构造与强度差异研究

竹节是竹子为适应其生存环境长期择优演化而形成的特殊构造,它对提高细长竹子的刚度与稳定性至关重要。但在竹的利用中,竹节对竹材的力学强度是否会有影响,说法不一。现以毛竹为研究对象,在比较了竹节间材和竹节之间的构造差异的基础上,以竹青、竹黄、竹节未处理和已刨平处理的两种试件形式,分析研究了毛竹的含节材与不含节的节间材在强度上的差异。结果表明,无论是自然状态下的竹材试件,还是刨去刨平青、黄、节的竹材试件,竹节对弯曲强度、顺纹剪切强度、抗压强度等力学性能均未见有降低的作用,相反还有着不同程度的增强作用。但竹节对竹材顺纹抗拉强度有着不可忽视的降低影响。     

龙竹的常压液体渗透性研究

采用常压渗透法对竹材液体渗透性进行了试验测定,以单位体积增重率作为评价指标对竹材液体渗透性进行了分析。研究结果表明:(1)预处理方式对竹材液体渗透性有影响,水煮处理竹材试件的液体渗透效果较好。(2)竹材构造对竹材液体渗透性有显著影响。未剖分含竹青和竹黄竹材试件的液体渗透性小于去掉竹青和竹黄的竹材试件的液体渗透性;不含竹节试件的液体渗透性优于含竹节试件的液体渗透性;竹材纵向的液体渗透性优于横向的液体渗透效果。(3)液体种类和液体浓度对竹材液体渗透性有影响,低浓度酸性染料渗透效果较好。(4)竹材液体渗透效果随含水率的升高而降低。     

以杉木积成材为芯板的新型细木工板的动态热机械分析

为了探索以杉木积成材为芯板的新型细木工板的动态热机械性能,利用动态热机械分析技术对新型细木工板进行了研究,结果表明:以杉木积成材为芯板的新型细木工板的储能模量(E′),随着试验温度的升高而迅速下降;损耗模量(E″)和损耗角正切(tan d),却随着试验温度的升高而迅速上升;其使用环境温度不能高于88℃。     

获得土体回弹模量的方法研究

指出了回弹模量做为一种表征土体却荷回弹性质的参数，室内土工试验可以获得，但试验周期较长，成本较高，因而只有在重要工程中才要求试验测试，一般工程只要求测试土体的压缩模量。通过搜集45套回弹模量与压缩模量的试验数据，在统计分析的基础上进行了回弹模量取值研究，成功的建立了回弹模量经验模型，模型计算值与试验测试值吻合程度很好，为获得回弹模量提供了一种新途径。     

Stiffness moduli of various softwood and hardwood species determined with ultrasound

Abstract

Comprehensive data sets of the elastic constants are available for only a few European wood species. The goal of this study was to provide stiffnesses for the principal directions and planes for further selected European softwoods and hardwoods, to extend the currently existing data sets. For this purpose, a dynamic technique was chosen: the moduli were estimated on the basis of sound velocity and density measurements. The collected data may be helpful for specialists in the relevant research and practical fields, particularly when stresses and strains of structural elements have to be calculated using modelling approaches.     

加速度计质量和安装位置对木材材料常数测试值的影响分析北大核心

为考察加速计质量和安装位置对木材测试频率的影响,设计了用自由梁和悬臂梁测试一阶弯曲频率以及用自由板测试一阶扭转频率的试验方案。根据能量法和振型推导出适用于计入加速计质量和安装位置影响的弹性模量和自由梁、悬臂梁的一阶弯曲频率的修正关系式以及剪切模量和自由板一阶扭转频率的修正关系式。应用加速度计为传感器实测了西加云杉梁、板和定向刨花板(OSB)沿其长度方向的一阶弯曲频率和一阶扭转频率,验证了导出的修正关系式应用于测试材料弹性模量和剪切模量的有效性,并以加速度计质量m和试件质量M之比m/M为参数,探讨了上述导出的修正关系式的适用范围。     

Estimation of shear moduli of wood by quasi-simple shear tests

A quasi-simple shear test, which is the most direct method for examining the shear properties of sheet metals, has been applied to measure the shear moduli of wood. Buna (Fagus crenata Blume) with variously sized shear regions was used for the test specimens. Strain gauges were mounted in the center of the shear regions to measure the shear strains. The shear tests were carried out to determine the shear moduli in the radial and tangential planes. Apparent shear moduli obtained from the experimental results were corrected by finite element method (FEM) simulation of the shear region, where both shearing and bending are produced. It was found that the corrected shear moduli are roughly independent of test conditions, and their values are in good agreement with the data obtained from bending-shear tests. This suggests that the method employed here can effectively estimate the shear moduli of wood.Part of this research was presented at the 50th Annual Meeting of the Society of Materials Science, Osaka, May 2001     

薄板类中密度纤维板动静态弹性模量的检测

植物挥发物在植食性昆虫的寄主选择和产卵选择中起着重要作用(杜家纬,2001).薄板类中密度纤维板的弹性模量(MOE)是表征其力学性能的主要指标之一.传统都是采用简支静曲测试方法,该方法过程繁琐、消耗时间长(赵仁杰等,2003;Ross et al.,1998).依据振动法测定木质材料的力学性能,过去几十年来已经被证明是一种成功的方法(Moslemi,1967;Ross et al.,1994),测定结果显示振动法测得的力学性质与传统静态弯曲测得的弹性模量间有非常好的一致关系.     

Evaluation of rolling shear strength of plywood by flexural vibration method

The rolling shear strength of plywood was evaluated using a flexural vibration test. Test specimens were lauan and Douglas fir three-ply plywoods made from thick veneers. The dynamic shear and Young's moduli were determined using the flexural vibration method, which involved in-plane and out-of-plane flexural vibration. The rolling shear strength was determined using the static destructive method, which is dependent on the direction of the lathe check in the core veneer. Before and after accelerated aging treatments were conducted, there were relations between out-of-plane dynamic properties (out-of-plane shear and Young's moduli) and its rolling shear strength. It was concluded that the rolling shear strength is related not only to the shear property of the core but the flexural stiffness of two faces when the deformation of out-of-plane plywood was not restrained.Part of this work was presented at the 47th Annual Meeting of The Japan Wood Research Society, Kochi, April 1997     

纤维板的静曲弹性模量及静曲强度的动态检测

利用振动无损检测法测得纤维板的动态静曲弹性模量,并用一元和二元回归分析了纤维板的密度、静态静曲弹性模量、动态静曲弹性模量、静曲强度之间的相关性。结果表明:纤维板的静态静曲弹性模量与动态静曲弹性模量之间,或动态静曲弹性模量与静曲强度之间均密切线性相关;以纤维板的动态静曲弹性模量和密度为自变量与静曲强度建立的二元回归方程,其相关程度较一元回归更为密切。密度及长度与横截面面积比值较大的纤维板,其动态静曲弹性模量与静态值较为接近。     

超声波预测落叶松规格材的抗弯性能

用超声波法测量落叶松规格材的动态弹性模量(DMOE),用弯曲试验测量其静态抗弯弹性模量(MOE)和抗弯强度(MOR),分析DMOE与MOE和MOR的相关性。研究结果表明:落叶松规格材的DMOE值比MOE高;DMOE与MOE和MOR的相关性均在0.01水平显著,DMOE与MOE的相关性高于DMOE与MOR的相关性。     

Prediction of the buckling stress of intermediate wooden columns using the secant modulus

We made several buckling tests of wooden columns with intermediate slenderness ratios () and examined the empirical formulas. On the basis of the examination, we formulated an equation for predicting the buckling stress () of an intermediate wooden column. Sitka spruce (Picea sitchensis Carr.) and buna (Japanese beech, Fagus crenata BI.) were used for the studies. A compressive load was applied on the specimen supported with pin ends, and the buckling stress was predicted by the tangent modulus theory and two empirical equations: those of Tetmajer and Newlin-Gahagan. The predicted - relations were compared with the test results, and the applicability of these predictions were examined. Based on the comparisons, we formulated an equation that can predict the - relations of materials with various stress-strain characters in the plastic strain range.     

竹木复合板与竹木复合层积材的抗弯性能

采用成熟的竹木复合集装箱底板制造工艺,根据不同的组坯方式,用竹帘及杨木单板压制成竹木复合板和竹木复合层积材。该工艺的创新点在于只将杨木单板浸胶,而竹帘直接干燥铺装,以减少人工操作对竹帘的破坏。通过研究两种板的抗弯性能,发现其顺向抗弯性能非常好,可将其分别作为集装箱底板和建筑结构用材。此外,针对竹木复合板性能不稳定的问题提出了改进方案。