人工林杨木材性对单板层积材强度的贡献率

本文提出了衡量单板层积材强度中实木材性所占份额的贡献率概念,以揭示实木材性对单板层积材强度的贡献程度。以人工林杨木为对象,研究了实木材性对单板层积材强度的贡献率。结果表明,实木材性好或单板层积材中的单板较厚时,贡献率较高。材性较优的６９杨和材性居中的７２杨、材性较差的６３杨３个无性系杨木的平均贡献率分别为７４３４％、６７４８％、６４７２％,厚度为３５６５ｍｍ、２６１４ｍｍ、１５４５ｍｍ单板组配的单板层积材中的平均贡献率分别为７４００％、６７４８％和５８０６％。研究的６项强度性能中,杨木实木材性对抗剪强度、弹性模量和冲击韧性的贡献率较高,约为８０％。     

人工林杨木的用途选择——实木或单板层积材

实木材性对单板层积材强度的贡献率可衡量单板层积材强度中源自实木材性的份额,是人工林杨木单项用途选择的基础。本文以３个无性系实体杨木和由３种不同厚度杨木单板分别组配的单板层积材为对象,以由贡献率引出的实木与单板层积材的份率差值为依据,研究得出人工林杨木的最终用途选择。结果表明：６９杨、７２杨和６３杨３个无性系杨木的平均份率差值分别为５７％、－１５％、－２９％,说明６９杨宜用作实木,７２杨和６３杨宜用作单板层积材;杨木用作不同组配结构的单板层积材时,实木与３５６５ｍｍ、２６１４ｍｍ、１５４５ｍｍ３种厚度单板组配的单板层积材的平均份率差值分别为４３％、－１３％和－４３％,说明实木与较厚的３５６５ｍｍ单板组配的单板层积材相比,杨木宜用作实木,与较薄的２６１４ｍｍ和１５４５ｍｍ单板组配的单板层积材相比,杨木宜用作单板层积材。不同荷载作用的结果下用途选择结果显示,在抗剪强度、弹性模量和冲击韧性３项性能上的份率差值为正,此时杨木宜用作实木;在抗弯强度、抗压强度和硬度３项性能上的份率差值为负,此时杨木则宜用作单板层积材。     

密实型杨木单板层积材制造技术

介绍了单板层积材、密实型单板层积材在国内外的研究和利用概况.探讨了采用低分子量酚醛树脂浸渍处理杨木单板的方法制备杨木单板层积材的生产技术.结果表明:施胶量相当时,浸渍方式与涂胶方式生产的单板层积材相比,密度相当,吸水厚度膨胀(24hTS)降低了24%,胶合强度提高了:16%,弹性模量(MOE)和静曲强度(MOR)分别提高了20.17%和44.76%.采用浸渍树脂方式生产的密实型强化杨木单板层积材随着吸药量的增多,密度增大;24hTS减小;胶合强度随着吸药量的增加先增大而后趋于平稳;MOE和MOR先增大后减小.当吸药量为168%时,MOE、MOR达到最大,分别为15.34GPa和135.31 MPa.密实型强化单板层积材能够满足建筑和木结构等结构材要求,具有良好的发展空间.     

几种人工林树种单板层积材的生产试验及力学性能研究

主要介绍了我国单板层积材的发展状况,几种人工林木材单板层积材的研制工艺和生产技术。通过不同树种制得的单板层积材的静曲强度和弹性模量的对比,发现无论垂直或平行加载,静曲强度和弹性模量与树种及材性关系甚大,桉树等高密度树种呈现较高的静曲强度和弹性模量,而用杨树制得的单板层积材具有较小的静曲强度和弹性模量。而水平剪切强度无论是垂直还是平行加载对树种差别不大。     

高湿状态下单板层积材的横纹承压性能

重组加工是提高低强度木材结构性能的重要手段,以杨木重组加工的单板层积材为研究对象,从受力方式、承压方向及增强方法等方面研究了高湿状态下单板层积材的全表面、局部表面及尽端局部表面横纹承压性能。结果表明：湿环境对杨木单板层积材横纹承压性能影响较大,湿环境下其全表面横纹承压性能为干环境下的33%;杨木单板层积材横纹承压性能主要与其承压位置与承压方向有关,局部横纹承压时受到承压面周围木材纤维的支持作用显著,承压面平行于单板层时其局部承压强度最高,在干燥环境下,分别是尽端局部及全表面横纹承压强度的1.2倍和1.4倍。单板层积材结构是导致不同承压方向横纹承压性能差异的主要原因,承压面垂直于单板层时,单板层积材易过早发生分层或屈曲破坏。湿环境下单板层积材含水率较高材质较软,自攻螺钉支持作用明显,有助于改善其承压性能。杨木单板层积材横纹承压强度对环境湿度较为敏感,在工程应用时应保持环境干燥并使承压面平行于单板层。     

杉木小径材制造单板层积材技术的研究开发

利用人工林杉木小径材制造单板层积材对于高效利用小径材资源和缓解结构用木材供需矛盾具有十分重要的意义。介绍了《杉木小径材制造单板层积材及应用研究》课题组利用杉木小径材制作单板层积材的研究过程、工艺开发、设备制造和产品应用方面所作的工作和研究成果。     

单板密度β射线检测法的研究

单板是制造层积材、胶合板等人造板材的基础材料,其密度对人造板材的机械、物理性能影响很大.对单板密度进行快速无损检测具有较高的实用价值.本文在分析国内外木材密度检测现状的基础上,提出了一种以计算机为核心的可以在线、无损检测单板密度的β射线检测法,并研究了系统的实现原理.     

单板厚度对杨木单板层积材强度性能的影响

单板厚度是影响单板层积材（英文缩写LVL）强度性能的主要因素之一，在同样的工艺条件下，单板越厚，LVL的剪断强度越低，剥离率越高。冷压胶合制造非结构单板积材时，建议采用4mm厚的单板     

人工林杨树木材性质与单板和胶合板质量关系的研究

本文以生长在3种长江滩地类型(江滩、洲滩、湖滩)、3种栽植密度(3m×4m,4m×5m,5m×6m)下的3个品系人工林杨树木材[欧美杨无性系72杨(Populus×euramericana cv.I-72/58),美洲黑杨无性系63杨(P.deltoides cv.I-63/51)和69杨(P.deltoides cv.I-69/55)]为对象,深入地分析了人工林杨树木材材性与单板和胶合板质量之间的关系.结果表明,72、63、69杨木材旋切和制胶合板均能获得较低的单板厚度偏差和背面裂隙率及较高的胶合强度.72、63、69杨单板厚度偏差与解剖性质中的纤维宽度、导管比量、木纤维比量在0.01水平下相关极显著,与纤维长度、胞壁厚度、壁腔比、腔径比、导管长和木射线比量在0.05水平下相关显著;单板背面裂隙率仅与胞腔直径在0.05水平下相关显著,与其它解剖性质相关不显著;胶合板的胶合强度与解剖性质相关最密切,其中与纤维长度、纤维宽度、胞腔直径、胞壁厚度、壁腔比、导管长、导管弦向直径、微纤丝角、导管比量、木射线比量在0.01水平下相关极显著\.与木纤维比量在0.05水平下相关显著.72、63、96杨木材单板厚度偏差和单板背面裂隙率与木材化学性质(pH,酸、碱缓冲容量)之间的关系不密切;胶合板的胶合强度与边材pH值在0.05水平下相关显著,与心材pH值以及心、边材的pH均值达到0.01水平相关极显著,与木材的碱缓冲容量在0.05水平下相关显著.72、63、69杨木材单板厚度偏差和胶合强度与木材物理、力学性质关系不密切;单板背面裂隙率与木材抗弯弹性模量在0.01水平下相关极显著,与气干密度在0.05水平下相关显著.     

竹板增强单板层积材组合梁受弯性能

单板层积材加工成梁构件应用于建筑结构材时,由于材料本身的强度和刚度不足,其结构构件不能满足现代多、高层以及大跨度建筑的需求。竹集成材是原竹经过切削成竹片、低温干燥、碳化、涂胶,再同方向平面或侧面组坯、热压胶合而成的竹基复合材料,其力学性能与稳定性优于木材。将集成竹材作为增强材料用于加固单板层积材梁是一种简单有效的提高梁极限承载力的方法。通过进行竹板增强单板层积材组合梁四点弯曲试验,研究了集成竹板对单板层积材受弯性能的增强效果。结果表明,在单板层积材受弯构件上下部粘贴集成竹板可提高构件极限承载力10%～50%。同时,考虑单板层积材和集成竹材料的非线性,推导出了适用于组合梁的极限承载力计算公式,计算结果与试验结果吻合良好。     

杨木单板实木门的制造工艺及应用研究

探讨了利用速生杨木单板层积材及科技木生产实木门的可行性,介绍了杨木单板实木门的制造工艺。速生杨木单板层积材压缩率、硬度、抗弯强度、尺寸稳定性等指标均远高于普通板材,是一种很好的结构用材,可用其替代高档硬质实木使用,以提升杨木产品的科技含量和附加值。     

Properties of curved laminated veneer lumber made from fast-growing species with radiofrequency heating for use in furniture

Curved laminated veneer lumber (LVL) is manufactured from glue-coated pieces of rotary-cut veneers assembled and pressed between molds. In this study, curved LVLs were produced from two fast-growing wood species such as massion pine (Pinus massoniana Lamb.) and poplar (Populus euramericana CV. I.) for use in furniture. In addition to the applicability of the two wood species used, the optimum technological conditions of curved LVL production with radiofrequency (RF) heating and the physical and mechanical properties of curved LVL were investigated. The results are as follows: (1) Curved LVL made from massion pine and fast-growing poplar shows excellent mechanical properties. These fast-growing wood species are suitable for curved LVL being used as furniture structural members. (2) The mechanical properties of curved LVL are affected by frequency, voltage, RF application time, and moisture content, with the RF application time and moisture content having more important effects on the mechanical properties than the frequency and the voltage. (3) The mechanical properties of curved LVL increase with a linear increase in the density of curved LVL.The abstract of this study was presented at the 9th Annual Meeting of the Chugoku Shikoku Branch of the Japan Wood Research Society, Tottori, October 4, 1997     

Compression control and its significance in the manufacture and effects on properties of poplar LVL

Summary In order to control the compression effectively, the main processing parameters for hot-pressing of poplar LVL were investigated in this study. Results from an orthogonal experiment show qualitatively that compression of poplar LVL is influenced by pressing pressure and moisture content of the veneers. High press pressure and veneer moisture content lead to high compression during hot pressing. It is shown that compression has significant effects on modulus of elasticity, modulus of rupture, specific gravity and thickness swelling of poplar LVL. Modulus of elasticity, modulus of rupture and specific gravity appear to be directly proportional to compression within the compression range of 5% to 20%. Horizontal shear strength results indicate that, due to inadequate contact, proper glue bond may not be achieved between veneers of LVL with low compression. Thickness swelling appears not sensitive to compression between the compression range of 4% to 10%.The authors wish to acknowledge the financial support from the Natural Sciences and Engineering Research Council of Canada to this study, which was carried out when the first author was a visiting scientist at Wood Science and Technology Centre, University of New Brunswick, Canada. The veneers and adhesive used in this study were provided by Temlam Inc., Ville-Marie, Quebec. Their contribution is gratefully acknowledged.     

Comparative study on physical and mechanical properties of laminated veneer lumber and plywood panels made of wood from fast-growing <Emphasis Type="Italic">Gmelina arborea</Emphasis> trees

Laminated products, such as laminated veneer lumber (LVL) or plywood (PW), have become important recently. The objective of this study was to determine and compare properties of panels fabricated with veneers of Gmelina arborea trees in a fast-growth plantation and glued with phenol formaldehyde resin. The results showed that LVL and PW physical and mechanical properties are comparable to those of solid wood with a specify gravity of 0.60. Moreover, these panels can be cataloged into group 2 of PS 1–95 of the Voluntary Products Standard of the United States. The difference in physical properties was not statistically significant between LVL and PW panels, except for water absorption. Some mechanical properties, such as hardness and glue-line shear, modulus of rupture in perpendicular flexure, nail and screw withdrawal parallel, and perpendicular strength, were statistically different between LVL and PW. However, no differences were established for the modulus of elasticity, tensile strength parallel to the surface, or tensile strength perpendicular to the surface. The differences were attributed to the venners’ orientation in the panels studied.     

Yield and mechanical properties of veneer from Brachystegia nigerica

In an effort to find suitable wood from natural forest to meet the demand for veneer products, the yield and tensile strength of veneers produced from Brachystegia nigerica were investigated. Two trees of B. nigerica were separately selected from 10 different natural forest zones while two logs were obtained from each tree. The logs were debarked and steamed in a vat prior to rotary peeling and slicing for veneer production. The optimum steam temperature was determined by considering different temperatures: 50°C, 60°C, 70°C, 80°C and 90°C for 24 h. Thereafter, optimum steam time was determined at the optimum temperature by considering durations of 24, 48, 72 and 96 h. The average taper of 0.75 mm per 1.0 m length was recorded for B. nigerica, indicating that the logs were reasonably cylindrical; thereby its logs are good for the production of veneer. The yield ranged from 44% to 61% with an average of 52% of the log input. The tensile strength of the veneer was tested perpendicular to grain and both peeled and sliced veneers had the highest tensile strength between 70°C and 90°C, suggesting that softening of wood polymers, especially lignin, is between 70°C and 90°C. The optimum temperature and time for veneer production are 70°C and 48 h, respectively. Commercial production of veneer from B. nigerica is feasible based on the yield and mechanical properties of the obtained veneer, thereby encouraging the expansion of the scope ofits utilization.     

Long-term material properties of circular hollow laminated veneer lumber sections under water saturation and cement alkaline attack

ABSTRACT

Innovative beech laminated veneer lumber (LVL) circular hollow sections for the use as temporary geotechnical soil nailing systems are currently being developed. Due to the permanent subsoil cement embedment, combined with high water saturation and permanent loading, the timber sections will lose strength and stiffness over time to a degree currently unknown. This paper presents the tensile and bending material properties of flat and curved beech LVL under various periods of immersion in a water–cement grout solution aiming at inducing both water saturation and long-term alkaline attack of the timber. In total, 824 and 279 samples were tested in tension and bending, respectively. Results show that samples manufactured from 3?mm thick veneers result in tensile strength and stiffness 17% and 24% higher, respectively, than samples manufactured from 2?mm thick veneers. A reduction in the initial bending and tensile strength of up to 70% was found after 90 days of water saturation and cement contact. Taking into account a duration of load factor for permanent loading of two years, it is recommended to reduce the short-term tensile and bending strength of beech circular hollow sections to be used as geotechnical anchors by 80%.     

Properties of red maple laminated veneer lumber impregnated with waterborne micronized and two soluble copper formulations

ABSTRACT

Certain important quality parameters of red maple (Acer rubrum) laminated veneer lumber (LVL) impregnated with three waterborne formulations: copper azole (CA-B), micronized copper azole (MicroCA or MCA) and alkaline copper quaternary (ACQ-D) bonded with phenol formaldehyde or cross-linked polyvinyl acetate (XPVAc) adhesives were evaluated. Pre-dipping of veneers before LVL production and two post-manufacturing procedures, viz., vacuum-pressure and post-dipping of LVL, were applied. Maximum copper retention in pre-dip-treated, vacuum-pressure and post-dip-treated LVL was 1.4, 9.7 and 1.7?kg/m³, respectively. Copper retention in MCA-treated LVL was relatively lower than soluble formulations. Various physical, mechanical and bonding properties of treated LVL such as density, water absorption, swelling, flexural properties, hardness, tensile shear strength, delamination and wood failure (%) were studied and compared with untreated LVL. Little to negligible deleterious effect was observed on properties of LVL due to these chemical treatments. Analysis of variance results showed that most of properties of red maple LVL were not significantly different compared with those of untreated LVL. Therefore, vacuum-pressure impregnation process can be used to treat the red maple LVL with novel micronized copper formulations for increasing the service life of such products against biodegradation without affecting techno-mechanical quality parameters.     

不同因素对竹/木复合强化单板层积材MOE、MOR的影响

以杨木单板和竹帘为原料,采用低分子量水溶性酚醛树脂浸渍处理,通过干燥、组坯、热压等工艺制备竹木复合强化单板层积材。探讨了组坯方式、压缩率、热压温度、热压时间4个因素对竹木复合强化单板层积材弹性模量(MOE)和静曲强度(MOR)的影响。结果表明:表层为一层竹帘的竹木复合强化单板层积材的MOE和MOR较大,分别是13．43GPa、148．13MPa,与表层为杨木单板次表层为竹帘组坯方式相比分别增加了33．63％、56．16％。确定了竹木复合强化单板层积材较合理的制造工艺参数。