共查询到18条相似文献，搜索用时 421 毫秒
1.
人工林杨木的用途选择——实木或单板层积材 总被引：9，自引：0，他引：9
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３５６５ｍｍ、２６１４ｍｍ、１５４５ｍｍ３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３５６５ｍｍ单板组配的单板层积材相比,杨木宜用作实木,与较薄的２６１４ｍｍ和１５４５ｍｍ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。 相似文献
2.
人工林杨木材性对单板层积材强度的贡献率 总被引：3，自引：0，他引：3
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%. 相似文献
3.
１９９０年引进３５／６６，７４／７６杨等黑杨派６个新无性系，经５年多引种选择试验表明，３５／６６，ＪＰ７，ＪＰ１８和７４／７６杨具有明显的生长优势分别比６９杨材积增加７４．４％，６７．２％，２９．９％和２５．２％比７２杨增幅，１３．７％～５８．４％，３５／６６和ＪＰ７杨不仅速生，且树干通直圆满，干材率高，是培养优质大径旋切单板的理想品种，７４／７６和ＰＥ４－６８杨分枝角度小，树冠趋光敏感性不强，是 相似文献
4.
5.
6.
经分析计算，基本密度为０．３６ｇ／ｃｍ￣３的木材，在１２０％的含水率状态下木材中细胞壁物质、水和空气三者的体积比约为１：１：１，因此当该木材体积压榨率达到６６％时，木材中的水分（自由水）几乎将被全部挤出。据此，使用表面有沟槽的几种不同模板对速生树种Ｉ－６９杨和火炬松的生材单板进行了不同压榨车的挤水试验，结果表明：Ｉ－６９杨２．０２ｍｍ生材单板用７０％的压榨率挤压后，含水率显著降低，组内试件间的合水率差异显著缩小；火炬松２．３８ｍｍ和３．３３ｍｍ生材单板，压榨率６０％比４０％的挤水量大、挤后与挤前组内含水率极差比值小，因而达到了降低并均匀生材单板含水车的目的。另外，模板不同也显出不同的挤水效果。 相似文献
7.
8.
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. 相似文献
9.
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。 相似文献
10.
单板密度β射线检测法的研究 总被引：1，自引：1，他引：1
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. 相似文献
11.
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。 相似文献
12.
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 相似文献
13.
Compression control and its significance in the manufacture and effects on properties of poplar LVL 总被引：1，自引：0，他引：1
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. 相似文献
14.
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. 相似文献
15.
Babatola Olufemi 《林业研究》2012,23(2):295-298
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. 相似文献
16.
《Wood material science & engineering》2013,8(3):142-156
ABSTRACTInnovative 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%. 相似文献
17.
ABSTRACTCertain 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. 相似文献
18.
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。 相似文献