薄型单板层积材结构改进的研究

薄型单板层积材(LVL)可替代锯材,应用于木质门窗构件等轻载结构领域.由于单板全部顺纹组坯,导致产品存在横向翘曲变形的技术问题.为此,尝试采用"部分单板横纹组坯"和"纤维板与单板复合"两种方法进行改进,制造了15 mm厚LVL,包含1～2层单板横纹组坯或1～2层3 mm纤维板.测试结果表明:单板横纹组坯.显著降低了LVL的抗弯性能,但LVL的弹性模量仍能达到单板层积材国家标准中70E级别的要求,而静曲强度甚至超过180E级别优等品的限值;与此同时,改进结构的LVL吸水翘曲变形显著降低.横纹单板越靠近LvL表层,板子抗弯性能降低越显著,而翘曲变形改善越明显.采用纤维板与单板复合制造LVL,纤维板的内结合强度衰减明显,易受破坏.     

地铁车辆用铸铝座椅骨架设计及仿真分析

设计了一种新型的地铁车辆用座椅,该座椅骨架采用铸铝材料。对铸铝座椅建立有限元仿真模型,分析了静态载荷、动态载荷工况下铸铝座椅骨架的等效应力,结合铸铝本身的特性,对座椅骨架强度进行评估,验证其强度符合设计要求。     

结构用杨木单板层积材力学性能特征值的研究

根据美国ASTM D5456《结构复合木材产品评价规范》评价方法标准及美国工程木材协会PRL-501《单板层积材性能标准》,对国产杨木单板层积材力学性能进行了检测和评价分析。通过拟合优度检验,发现杨木单板层积材力学性能与对数正态分布拟合得较好。杨木单板层积材力学性能特征值的研究可为我国结构用单板层积材特征值确定方法提供参考。     

玻璃纤维增强结构用单板层积材热压工艺研究

通过玻璃纤维增强速生杨木制备杨木单板层积材(LVL),可提高杨木的强度等级,使其达到结构集成材层板的使用要求。采用正交实验方法,研究温度、时间、压力、偶联剂浓度、涂胶量对杨木单板层积材弹性模量、静曲强度、剪切强度的影响,其中主要研究热压工艺对力学强度的影响,得出的最优工艺参数为:热压温度130℃、时间100s/mm、压力1.2MPa。     

智轨电车座椅骨架强度分析及结构优化

为实现智轨电车减重降本的目标,对座椅骨架进行强度分析及结构的优化设计.首先利用Creo和HyperMesh对座椅骨架进行三维建模和网格划分;然后将有限元模型导入ANSYS进行模态分析和强度分析,得到座椅骨架的前六阶固有频率和最大应力;最后根据有限元结果进行结构优化,以实现座椅骨架的轻量化设计.对比优化前后的有限元计算结...     

基于有限元模拟的单板层积材纵Ⅱ型切屑形成机理

研究单板层积材切削加工中纵Ⅱ型切屑形成机理,通过对材料几何模型、力学模型和切屑分离等关键物理环节建模,建立切削加工的有限元模型,并利用该有限元模型模拟纵Ⅱ型切屑形成的全过程,通过分析切屑的形成过程以及该过程中的切削力和应力应变的变化规律,利用有限元软件的模拟功能,得到其切屑的形成过程和切削过程中工件的应力、应变分布及切削力的变化情况,有效揭示纵Ⅱ型切屑形成的内部因素。     

结构用慈竹单板层积材的制备工艺与性能

以慈竹和毛竹为材料,采用竹材纤维可控分离技术,在去除竹青和竹黄后,制造竹材单板层积材,并测定板材的性能.结果表明:以去青黄竹材压制单板层积材的性能,高于未处理竹材;慈竹单板层积材的性能高于毛竹;随着密度的增大,30 mm厚慈竹单板层积材的力学强度提高,可达到集装箱底板用胶合板和风电叶片材料的标准要求.     

基于超声波回波分析的单板层积材质量检测系统

系统提出一种以超声波回波分析理论建立检测模型的方法,以单板层积材为研究对象,通过超声波换能器探头对其质量进行无损检测,并对超声波回波进行时域及频域实验分析和讨论.分析了FFT变换后的频谱图,通过对比频谱图可判断出单板层积材的质量,实现在线检测.     

杨木单板层积材足尺力学性能特征值测试分析

采用足尺测试方法,对杨木单板层积材的力学性能特征值进行测试;分析了不同生产工艺条件下,不同承载方向和不同规格尺寸的杨木单板层积材力学性能特征值的差异性。     

结构单板层积材标准对比及测试评价方法探讨

通过分析2个结构单板层积材国家标准,简述了结构单板层积材标准框架及技术内容对比,介绍了结构单板层积材足尺检测和评价方法及尺寸效应,为新标准的实施奠定了应用基础。     

增强型杨木单板层积材力学性能分析

采用玻璃纤维布与碳纤维布复合材料及分步热压法增强杨木单板层积材,研究了玻璃纤维布与碳纤维布复合材料的铺设位置及分步热压法对杨木单板层积材力学性能的影响.结果表明:两种增强方式对杨木单板层积材静曲强度(MOR)和弹性模量(MOE)的增强效果均较明显;采用对称铺设相同的增强材料时,铺设位置靠近杨木单板层积材表层时对MOR和MOE等力学性能的增强效果较铺设在靠近芯层时的增强效果明显;采用分步热压法可以明显改善单板层积材水平剪切强度.     

Outdoor exposure tests of structural laminated veneer lumber (II): evaluation of the strength properties after nine years

To investigate the durability of structural laminated veneer lumber (LVL), outdoor exposure tests have been conducted since 1990 at a field-testing site at the Forestry and Forest Products Research Institute. This article is the second interim report on the results after 9 years of exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the tests. Almost all the exposed specimens were decayed by a kind of brown rot fungi (Pseudomerulius aureus (Fr.) Julich). The degree of decay varied with wood species; grand fir and western hemlock LVL in particular showed weak resistance against the decay. All the specimens were stored for more than 1 year in a testing room conditioned at 20°C and 65% relative humidity. We then measured the ultrasonic velocity of the specimens by the Pundit method, penetration depth by the Pilodyn method, and bending strength by a conventional bending test. Correlation between nondestructive measurement factors and the density was strong even on LVL with many adhesive layers. The nondestructive testing method was found to be applicable to LVL as well as solid lumber. After the nondestructive measurements, each LVL was cut into three types of specimen (top: T, middle: M, and bottom: B) for the bending tests. The bending strength varied with the type of specimens. Correlation between modulus of elasticity and modulus of rupture was strong even in the decayed specimens.     

单板接缝对LVL力学性能的影响

将LVL中的单板接缝分别配置在表芯层、同一垂直面上、错开的相邻层,并对所测得的力学性能进行分析,结果表明:除最外3层同位接缝外,其他接缝板材的3点弯曲和4点弯曲静曲强度和弹性模量都大于无接缝板A。同位接缝的水平剪切强度按接缝11,5,6,7和9层递增。表背3层接缝错开对板材的静曲强度提高幅度高于芯层5层接缝错开的影响;弹性模量在表背3层随着接缝错开距离的增加而升高,随着芯层5层接缝错开距离的增加而减小。     

Outdoor exposure tests of structural laminated veneer lumber I: evaluation of the physical properties after six years

To investigate the durability of structural laminated veneer lumber (LVL), outdoor exposure tests have been conducted since 1990 at a field-testing site at the Forestry and Forest Products Research Institute. This paper is an interim report on the results after 6 years' exposure. Seven kinds of structural LVL with no preservative treatment were subjected to the tests. These specimens were sampled at the testing site each year and then stored for more than 1 year in a testing room conditioned at 20°C and 65% relative humidity. We then measured the modulus of elasticity (MOE) by longitudinal vibration frequency, the penetration depth by the Pilodyn method, weight loss, color difference (E ^*) by the CIEL ^* a ^* b ^* system, swelling, compression strength, and bending-shear strength. Deterioration caused by outdoor exposure was obvious in the color, weight, MOE, and compressive strength of LVLs, but not in the penetration depth by the Pilodyn method or the bending-shear strength. The retention values of MOE and compressive strength after 6 years of exposure were 78% and 77%, respectively. The difference in durability among material species was not significant in general, except that heavy decay by brown rot fungi took place on some of the grand fir specimens. It should be noted that no significant delamination occurred in any of the adhesive layers, although slight checks developed on the surface of the specimens.     

混合组坯对杨木单板层积材弹性常数及力学性能的影响

单板层积材具有结构均匀、强度高等优点,材料、结构、制造工艺等差异对其性能影响显著。以13层22 mm厚全顺纹、2层及3层横纹其余顺纹混合组坯的杨木单板层积材为对象,通过电测法、三点弯曲及拉伸实验,对其主要弹性常数及力学性能参数进行测试,得出以下结论:1)随着横纹层数的增加,顺纹方向的弹性模量下降,横纹方向的弹性模量增加,层积方向的弹性模量先减小后增加,单板层积材的各向异性降低;2)随着横纹层数的增加,静曲强度减小,变异性逐渐增大,进行结构设计时需更多考虑材料的性能稳定性;3)组坯方式对LVL抗拉强度的影响不大,适当增加横纹层板可提高抗拉强度;4)组坯方式对泊松比的影响较大,随着横纹层数的增加,泊松比总体降低,采用纵横混合式组坯可能有利于抵抗由拉、压载荷所造成的材料变形。     

尾巨桉/金属复合材料层间剪应力分布特征的有限元解析

利用三层尾巨桉单板之间嵌入与两张性能相同的金属薄板组成五层尾巨桉单板/金属网层积复合材,并采用预实验优化的热压工艺参数压制成板。采用大型通用有限元分析软件ANSYS 10.0建立了尾巨桉/金属网复合材料的有限元分析模型,模拟了尾巨桉/金属复合材料界面自由边附近与板材内部界面剪切应力分布规律,确定了最可能引起分层破坏的剪切应力的分布规律。结果表明:(1)复合材料四层界面处3个剪切应力的二维应力场分布云图表明自由边附近出现奇异应力的分布特征,自由边处剪切应力τxy的值最大,其最大值为14.0MPa;(2)复合材料四层界面处3个剪切应力的三维应力场分布云图表明在四层界面处剪切应力τxy的应力集中现象都最为明显,最大应力集中值可达25.0 MPa。     

Constitutive Equation of Laminated Veneer Lumber （LVL） at Large Deformation Condition

The stress-strain relation of laminated veneer lumber (LVL) was established by the method of regression, and its constitutive equation at large deformation and constant loading conditions was given to predict the static mechanical behaviors of LVL.     

Fire protection of a laminated veneer lumber joint by wood carbon phenolic spheres sheeting

Laminated veneer lumber joints made with metal plate connectors were protected with wood carbon phenolic spheres (CPS) sheeting and tested for creep under fire. The effects of the carbonizing temperature of charcoal, used as raw material for the CPS sheets, the thickness, and the location of the sheet on the joint regarding the fire-resistance performance of the joint were studied. The time to rupture of the joints covered with CPS sheets made from charcoal carbonized at 800°C (CPS800) was slightly prolonged compared with that of uncovered joints. On the other hand, the time to rupture of CPS sheets made from charcoal carbonized at 1600°C (CPS1600) was markedly extended. The changes in the charcoal properties due to increasing the carbonizing temperature might be the main reason the CPS1600 sheets had higher fire-resistance performance. The thickness and location of CPS1600 sheets have significant effects on the fire resistance of the joint. A highly fire-resistant laminated veneer lumber joint was obtained using a CPS1600 sheet. The CPS1600 sheet with a thickness of 3mm covering three sides of the joint prolonged the time to rupture 16-fold compared with that of unprotected joints.Part of this paper was presented at the 4th International Wood Science Symposium, Serpong, Indonesia, September 2002     

密实型杨木强化单板层积材制造工艺及应用前景分析

介绍了杨木强化单板层积材的制造工艺。杨木强化单板层积材的压缩率约为15％～40％，其硬度、抗弯强度、耐水性、尺寸稳定性等指标远高于普通单板层积材，可作建筑用木梁、立柱、水泥模板、家具、门窗、地板、车厢板、集装箱板等多种材料。它是一种很好的结构用材，市场前景十分看好。     

Fire-resistant performance of a laminated veneer lumber joint with metal plate connectors protected with graphite phenolic sphere sheeting

Creep under fire of laminated veneer lumber (LVL) joined with metal connectors was studied. The fire-resistant performance of LVL butt joints connected with metal plates protected with graphite phenolic sphere (GPS) sheeting was discussed. The GPS sheeting was overlaid on the joint in different sizes and locations. The joint was exposed to a burner with a top flame temperature of 800°C and loaded with a load of 200 N to test for creep under fire. The results showed that the fire-resistant performance of the joint was markedly improved by the sheeting. The size and location of the GPS sheet significantly affected the time to rupture of the specimen, which was six times longer than that without GPS. Temperature measurements at the joint showed that the GPS sheeting distributed the heat along the surface and delayed failure. Thermographic images and analyses clarified the improvement in fire-resistant properties due to GPS.