ANSYS在杨木-秸秆层合梁弯曲分析中的应用

利用ANSYS有限元程序包对杨木-秸秆复合材料层合梁的弯曲问题进行分析,并与各种理论和实验结果进行比较.结果表明,利用ANSYS进行杨木-秸秆复合材料应力和变形方面的数值计算研究具有较高的精度和准确性.     

杨木—秸秆层合梁失效分析与优化设计

分析了杨木一秸秆层合梁在弯曲变形中的失效情况,并根据实际需要,在层合梁结构总厚度一定的情况下,以梁的弯曲变形和弯曲应力为约束,以减少复合结构的总质量为目标,利用ANSYS有限元工程分析软件对梁的横截面结构尺寸进行优化设计.     

提高杨木线性振动摩擦焊接胶合性能的研究

研究了杨木线性振动摩擦焊接的干剪切强度、湿剪切强度和木破率。为提高杨木摩擦焊接的湿剪切强度与木破率,采用表面氧化、表面磺化以及表面涂覆的方式处理杨木板材,再经线性振动摩擦焊接进行黏合,使用万能力学试验机测得其剪切强度,对比表面处理前后剪切强度的变化,并利用傅里叶红外光谱分析了其表面处理前后基材和摩擦焊接层的化学基团变化情况,对胶合性能的变化做出解释。研究结果表明:杨木经过表面氧化磺化涂覆醋酸锌处理后,摩擦焊接层的干剪切强度为5.41 MPa,木破率为63%,与未处理的杨木相比,分别提高了48.22%和96.88%;湿剪切强度从0提高到1.34 MPa;摩擦焊接时厚度损失减少了46.4%。杨木分别经过表面氧化和表面磺化处理后,摩擦焊接层的干剪切强度仅为3.45和4.10 MPa,木破率为28%和42%,湿剪切强度为0.76和0.96 MPa。摩擦焊接层的红外光谱分析表明,经表面氧化磺化涂覆醋酸锌处理后,杨木中的纤维素和半纤维素分解,使木质素的相对含量有所增加,且活化了杨木中的—OH,与醋酸锌生成多醚,消耗了亲水性的—OH。     

用高阶剪切理论研究竹木复合空心板的弯曲性能

运用高阶剪切理论对竹木复合空心板的弯曲性能进行分析与研究。结果表明 :在跨高比较小时 ,横向剪切效应对板的弯曲性能有显著影响 ;预测的变形与一阶剪切理论基本相当 ;预测的强度能够反映出横向剪切效应的影响 ,其影响只与载荷大小有关 ,而与跨高比无关 ;描述横截面上的应力分布与一阶剪切理论显著不同 ,尤其是剪应力 ,不仅在跨中截面上存在较大差异 ,而且还随截面的位置而变。     

基于静态弯曲性能的木质工字梁设计计算方法探讨

参照钢质工字梁静态弯曲理论,对木质工字梁（IJ）的“荷载一位移”曲线、IJ正应力理论计算值与实测值、IJ整梁挠度理论计算值与实测值的对比分析,结果认定：1）钢质工字粱的静态弯曲理论计算公式,可用于IJ弹性段应力和挠度的分析计算;2）IJ整梁静态弯曲性能的分析计算时,应注意IJ上翼缘压缩特性和下翼缘拉伸特性的差异。     

浸渍塑化杨木单板顺纹弯曲性能研究

本研究以酚醛树脂为浸渍液,杨木单板为木材试样,对经浸渍塑化处理的杨木单板进行三点弯曲试验,探索了木/竹复合层合板的组分材料--塑化杨木单板受不同压力时的顺纹弯曲弹性性能,并分析了其与塑化压力间的关系.结果表明,塑化杨木单板的静曲模量和静曲强度与塑化压力呈非线性关系.通过对杨木单板试验研究,为木材/竹材复合材料制造过程中的结构设计和生产工艺提供一定的理论依据和基本思路,并对产品的设计、组织现场生产和产品质量评估提供一定的参考.     

正交胶合木平面剪切的开裂形貌及其破坏模式探究北大核心

从应力和应变分析,定量地论述了三点弯曲试验和改进的平面剪切试验皆能实现CLT垂直层的平面剪切。从将CLT垂直层的平面剪切处理为纯剪切的近似性考虑,CLT三点弯曲试验优于CLT改进的平面剪切试验。通过三点弯曲试验和改进的平面剪切试验测试了铁杉(Tsuga canadensis)CLT试件的载荷-位移曲线,并同步地对CLT垂直层的开裂形貌和开裂面的方位角进行观察和记录。应用对CLT垂直层的应力分析与其开裂面方位角相结合的分析方法探讨了CLT垂直层平面剪切的破坏模式。研究表明:三点弯曲试验和改进的平面剪切试验测试的铁杉CLT平面剪切强度值仅相差5.7%;CLT垂直层的横切面开裂形貌除轮裂和径裂外,还存在既不轮裂、又不径裂的新的开裂形貌;占试件总数63.3%的试件开裂破坏面的方位角在CLT垂直层的第一主平面方位角附近;CLT垂直层平面剪切存在拉伸和剪切等两种破坏模式。     

分离刚度法在单向竹篾积成胶合板机械性质测试中的应用研究

介绍了一种实用的材料机械性质测试方法-分离刚度法，用该方法实测了造船工业用的单向竹蔑积成胶合板的弯曲刚度与横向剪切刚度，对单向竹蔑积成胶合板梁弯曲变形的有限元计算与实测基本吻合的事实说明，分离刚度法的测试结果是可靠的。     

竹木复合板的拉伸与弯曲力学特性

竹木复合材料的拉伸和弯曲性能是其重要的力学特性,对其应用有十分重要的影响。通过动态电阻应变仪和电脑程控力学试验机对由竹席、竹帘和杨木单板组成的复合材料的拉伸和弯曲力学性能进行了研究。研究表明竹木复合板的纵向和横向拉伸应变与载荷之间具有显著的线性相关关系,泊松比和弹性模量与载荷之间呈非线性关系。随弯曲载荷增加,竹木复合板的弯曲应力、应变和变形均呈线性增加,但弯曲弹性模量呈非线性下降。泊松比、拉伸和弯曲弹性模量与载荷之间呈非线性关系,证明了该竹木复合板的弹塑性特征。     

正交胶合木(CLT)梁剪应力分析及其层间剪切强度测试

【目的】探索正交胶合木(CLT)矩形截面梁剪应力计算公式,为测试CLT梁层间剪切强度提供理论依据。【方法】根据胡克定律及梁的弯矩与剪力的微分关系,计算3层、5层和7层CLT梁及同向胶合木梁的层间剪应力,给出CLT梁剪应力计算公式,比较CLT梁及同向胶合木梁的剪应力分布特征。【结果】CLT梁层间正应力间断,但层间剪应力是连续的;对于CLT矩形截面梁,其剪应力沿截面高度变化趋于均衡,不再遵循抛物线分布; CLT短跨距梁在三点弯曲加载中,依次发生垂直层滚动剪切破坏、层间剪切破坏和平行层弯曲破坏;短跨距梁三点弯曲载荷-位移曲线的最高峰值载荷为CLT发生层间剪切破坏载荷,其值稳定、易于读取;铁杉CLT梁层间剪切强度与其平行层弹性模量呈正相关。【结论】CLT梁层间剪应力和最大剪应力与CLT层数、平行层与垂直层弹性模量比值E_L/E_T(或E_L/E_R)有关; 3层、5层和7层CLT矩形截面梁的最大剪应力均发生在梁截面中性轴上,其值分别为1.5倍截面平均剪应力的92.8%、86.7%和92.6%;短跨距梁三点弯曲法是一种有效测试CLT层间剪切强度的方法。     

大跨度竹质方梁的制备与抗弯性能研究

为了探究木质材料在大型建筑应用的可行性,以竹材为原料,利用层积热压组坯的方式制备长度为3 m和6 m的竹质方梁,对其进行四点抗弯测试,观察其在测试过程中的弯曲变形及破坏特征,分析弹性模量、静曲强度,根据其破坏形式分析竹质方梁结构及组坯方式对其抗弯性能的影响。结果表明:6 m竹质方梁弹性模量达10261.24 MPa,跨中竖向位移至86.97 mm而不破坏;3 m竹质方梁静曲强度达85.51 MPa。竹质方梁破坏均出现在弯曲的受拉面,且裂纹通过竹节处、胶合界面以及竹纤维排布方向蔓延,这与竹材本身结构特性有关。通过对3 m和6 m竹质方梁抗弯实验及分析,以期为竹质方梁在大跨度下的应用提供数据支撑。     

Estimation of stiffness and strength in timber knee joints with adhesive and verification by experiment

The use of adhesive joints is gradually increasing, especially those with glued-in steel rods (GIRs). There are, however, some problems with the design methods when used for moment-transmitting applications. In this article, design methods for GIRs and cross-lapped glued joints (CLJs) are proposed. For CLJs, we made a hypothesis that both rotational deformation of CLJ and stress of the glue line occurred with bending and shearing deformation of the timber. Using this hypothesis and Kelvin’s theorem, a mechanical model of CLJ is proposed. For GIRs, the axial stress component of the rod and the lateral stress component of the rod were taken into account using the theory of a beam on an elastic foundation. From the comparisons between calculations and experimental results, it was recognized that the stiffness and strength of CLJs and GIRs could be predicted precisely using our proposed models.     

木工字梁的挠度计算方法探讨

对木工字梁的挠度进行了公式推导、试验、计算和验证分析。结果表明，考虑剪切变形时，实测挠度值与预测挠度值非常接近；忽略剪切变形时，实测值和预测值相差非常大。理论和实测证明了在计算木工字梁挠度时剪切变形是不可忽略的。采用试验方法可以得到木工字梁的EI和K值，其可用于准确预测木工字梁的挠度，为木工字梁挠度计算和预测提供了一种比较简单的方法。     

Study on Physical and Mechanical Properties of Structural Laminated Bamboo Panel

In this paper, the physical and mechanical properties of laminated bamboo lumber were studied by testing moisture content, delamination ratio, horizontal shear strength, MOE and MOR of the structure-use material, in the same time, these subjects of finger-joint were tested too. The results showed that, the horizontal shear strength, MOR, MOE of laminated bamboo were superior to the ordinary structure-use timber in architecture, such as Pinus. The performance of aging test was not extraordinary, although the physical and mechanical properties of laminated bamboo lumber decreased after aging test, these properties were beyond Pinus yet.     

实木拼接板胶合性能及其破坏形式

对铁杉木、橡胶木和北美核桃木拼接板的胶层耐久性能、侧拼抗剪和指接抗弯强度进行了检验.结果表明:侧拼胶层通过Ⅰ类浸渍剥离试验要求,指接胶层不能完全满足Ⅱ类浸渍剥离要求,破坏形式主要有胶层开裂和边齿脱落 ;侧拼抗剪强度低于木材顺纹抗剪强度5％,指接抗弯强度是木材抗弯强度的26.2％～77.9％,破坏形式主要有指接胶层开裂、指榫折断及木材撕裂.     

Shear behaviour of bond lines in glued laminated timber beams at high temperatures

A comprehensive research project has been carried out at the Swiss Federal Institute of Technology (ETH) on the fire behaviour of timber-concrete composite slabs (Frangi and Fontana 2000). The glued laminated timber beams used for the fire tests were bonded with a one-component polyurethane (1-K-PUR) adhesive. As one fire test on a slab showed an unexpected shear failure of a glued laminated timber beam, a series of tests was carried out to study the shear behaviour of different types of adhesives at high temperatures. The first part of the paper describes the results of the shear tests at elevated temperatures, in the second part the shear test results are compared to the fire test on a slab.     

Incorporating size effects in the Tsai-Wu strength theory for Douglas-fir laminated veneer

Summary This paper elucidates the need to consider the effect of volume on brittle material strengths when these strengths are used in a strength theory. Specifically, Weibull weakest-link theory has been implemented with the Tsai-Wu strength theory to predict the ultimate load carrying capacity of a center point off-axis bending member made from Douglas-fir laminated veneer. Weibull theory has been used in two distinct ways to account for size effects needed to evaluate brittle material strengths (ie. tension perpendicular and parallel to grain, and shear) for the strength criterion. The analytical methods assume linear elastic, plane stress states and have been described and evaluated using probability theory as a framework. Analytical results are in reasonable agreement with experimental findings substantiating the techniques proposed herein.     

Finger joint performance of structural laminated bamboo member

The structural performance of finger-jointed laminated bamboo was investigated for two bamboo species by considering the finger length, profile orientation, lamination direction, culm growth height, and mechanical properties of bamboo materials. Based on the growth height variation and bamboo species, the best finger-jointed laminated bamboo was found for the lamina processed from the middle growth height of a moso bamboo culm with the finger profile shown on the width face of the beam. It was 38.7% higher in bending strength than the lowest group, with the lamina from the lower ma bamboo culm showing the finger profile on the thickness face of the beam. When considering the finger length and lamination orientation, the strongest finger-jointed laminated bamboo joined with an 18-mm finger, showing the finger profile on the width face of a vertically laminated beam was 50.1% higher in bending strength than the lowest group having a 12-mm finger showing the finger profile on the thickness face of a vertically laminated beam. The laminated ma bamboo showed higher finger-joint efficiency, 11.6%, than moso bamboo, and the members showing the finger profile on the width surface was 12.3% better in joint efficiency than that showing on the thickness surface of the beam.