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不同结构杨木单板层积材的蠕变和抗弯性能 总被引：17，自引：1，他引：17
本文研究了单板层积材(LVL)的压缩率、结构形式和增强方式对其蠕变特性、弹性模量以及静曲强度的影响。研究表明：在本研究范围内，提高LVL的密度和合理组坯是改善其力学性能和蠕变特性的较好途径；采用浸胶单板可适当改善LVL的力学性能；LVL的蠕变特性曲线同木材的相似，但其瞬时挠度一般大于瞬时弹性恢复值；通过提高LVL的静曲强度和弹性模量有望改善其蠕变性能。 相似文献
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对从10.9％吸湿到25％再吸水到33％,接着蒸发回到25％再解吸回到10.9％的一个循环内多点含水率(MC)下的意杨酚醛树脂单板层积材(P-PF-LVL)静曲弹性模量(MOE)的测试分析结果表明:仅一个周期(MC 10.9％～33％～10.9％)的增水和失水,就导致P-PF-LVL产生了31.36％初始MOE的永久性损失,其中,源自于热压压缩永久性厚度回复的有4.61％;初始MOE最大可下降56.66％,初始厚度最大可增加4.84％,其中,热压压缩的永久性厚度回复有2.76％.P-PF-LVL的纤维饱和点为25％左右,其特征与一般实木有所不同.研究结果有助于结构用LVL的设计、制造和性能控制. 相似文献
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桉木单板层积材生产工艺的优化 总被引：1，自引：0，他引：1
采用响应面法(RSM)和中心组合旋转设计(CCRD),研究了桉树单板层积材(LVL)的生产工艺条件,并对优化工艺所得的预测值进行了实验验证。方差分析结果表明:面粉添加量对桉木LVL的静曲强度(MOR)和弹性模量(MOE)有着显著影响,而热压温度和热压时间的影响不显著。通过回归分析,建立了相应的回归模型。回归模型的预测值与实验值的拟合良好,说明回归方程能用来预测和优化桉木LVL的力学强度性能。最佳工艺条件为:热压温度130℃,热压时间1.5 min/mm,面粉添加量5%(质量分数)。在此工艺条件下压制的桉木LVL垂直加载条件下的静曲强度(MOR⊥)和弹性模量(MOE⊥)分别为89 MPa和16 722 MPa,平行加载条件下的静曲强度(MOR∥)和弹性模量(MOE∥)分别为88 MPa和15 067 MPa,MOR和MOE分别达到了结构用单板层积材国家标准的优等品和140E级别。 相似文献
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基于静态弯曲性能的木质工字梁设计计算方法探讨 总被引：1，自引：0，他引：1
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。 相似文献
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利用兴安落叶松小径原木高频胶合制造单板层积材的研究 总被引：3，自引：0，他引：3
本文讨论了高频胶合制造小径落叶松LVL作结构材的工艺和强度性能;分析了板坯内部的温升速度;比较了高频胶合无缺陷LVL和冷压LVL、单板经CCA防腐处理的LVL以及有节子、有对拼LVL的性能指标;最后为了工业化生产的需要,进行了LVL大试样静曲强度试验。结果表明,用高频介质加热法制造LVL获得了普通热板热压法达不到的快速加热效果,弥补了小径材材质差、强度低的缺点。因此用小径落叶松原木制造结构用单板层积材是可行的。 相似文献
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热压工艺对定向刨花-单板复合集装箱底板性能的影响 总被引：1，自引：0，他引：1
采用不同的施胶量、热压压力、热压时间,研究定向刨花(Oriented Strand)作芯层、单板作面层的一次热压复合制造集装箱底板的热压工艺,以及底板的密度与力学性能之间的关系。结果表明:(1)当刨花的施胶量(MDI)为8%时,在与刨花接触的单板上不涂胶、涂MDI及涂WD型酚醛胶,对整块板的静曲强度的差异不大;(2)WD型PF胶适合作为一次复合热压工艺的单板间用胶黏剂;(3)延长卸压时间,可以减小板的回弹,理想的热压时间为27min;(4)复合集装箱底板的芯层密度对底板的静曲强度起决定性作用,当芯层密度低时,其破坏形式均表现为剪切破坏;(5)按3-D工艺压出的板的力学性能超过传统的克隆集装箱胶合板底板,可以作为集装箱底板使用。 相似文献
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为了提高速生杨木的综合性能,以脲醛树脂/钠基蒙脱土(UF-Na-MMT)插层复合材料为改性液进行改性处理.结果表明:速生杨木的密度、尺寸稳定性以及力学性能均能得到明显改善;随着改性液中Na-MMT比例的增加,其抗弯强度、抗压强度、弹性模量不断增加;当Na-MMT的用量为14%、UF树脂的用量为20%时能获得较好的改性效... 相似文献
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Since the structure of oil palm wood varies dramatically, the property gradients of oil palm wood within a trunk are of great interest. In this study, the physical (density, water uptake and swelling in the radial direction) and mechanical properties (bending modulus of elasticity and strength, compressive modulus of elasticity and strength in the direction parallel to the fiber, compressive strength in the direction perpendicular to the fiber and shear strength in the direction parallel to the fiber) of oil palm wood for a whole trunk were examined. The water uptake, compressive strength in the direction perpendicular to the fiber, shear strength in the direction parallel to the fiber, bending modulus of elasticity and strength and compressive modulus of elasticity and strength in the direction parallel to the fiber appeared to be independent of trunk height but tended to be related to the relative distance from surface or density by a single master curve. However, the swelling in the radial direction of the oil palm wood was not correlated with the relative distance from the surface, trunk height or density. Finally, property map of oil palm wood for a cross section at any height was prepared for practical use. 相似文献
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对3种追肥处理1(N300P200K200)、处理2(N200P100K150)和处理3(N100P50K50),从12、27、42、50、62、75、88、99、110、144到192月生的尾巨桉生长量数据进行了统计分析,并在198月生时对每种施肥处理取7株样木进行了木材的基本密度、抗弯强度、弹性模量、硬度、干缩率以及皱缩率等指标开展研究,结果如下:追肥量与生长量成正相关关系.追肥量越多,生长量越大,这种差距从追肥后就开始产生,一直到192月生时都存在;但是,这种差距在大部分时间里都未达到显著水平:达到显著差距的只有施肥处理1和处理3之间,27月生时DBH达到0.01的显著性差异、平均高在12、27和37月生时达到0.05的显著性差异、蓄积量在27、37、42和50月生时达到0.05的显著性差异.材性指标上,大径材木材材性与追肥量的关系密切,增大施肥会影响木材材性,包括降低抗弯强度,增加弹性模量,降低端、径面和弦面硬度,降低基本密度,增加木材含水率等;达到显著差异的有:木材的抗弯强度、径面硬度被显著降低,达到了0.05的显著水平.木材边材基本密度降低更大,达到了0.01的极显著水平.经过多重比较的分析,都是常规施肥处理3与处理2和常规施肥处理3与处理1两两之间差异显著.处理1和2比处理3的抗弯强度平均分别降低了12％和14％、径面硬度分别降低了11.7％和14.1％,而边材基本密度分别降低了8.6％和8.1％;因此,在培育桉树大径材时,一定要考虑合理施肥量. 相似文献
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毛竹竹材物理力学性能研究 总被引：5，自引：0，他引：5
为了解不同竹龄毛竹生材含水率、线性干缩率、气干密度、抗弯强度、抗弯弹性模量和顺纹抗压强度等物理性能,对其加工应用的影响,笔者以2-7年生毛竹为材料进行研究,结果表明：竹材的生材含水率、气干干缩率（弦向、径向、纵向）和全干缩率（弦向、径向、纵向）随着竹龄的增加呈减小的趋势;从基部到梢部竹材的生材含水率、线性干缩率均减小;竹材线性干缩率弦向＞径向＞纵向.竹材气干密度、抗弯强度、抗弯弹性模量和顺纹抗压强度均随着竹龄的增加呈增大的趋势,尤其是3年生竹材的这些物理力学性能与2年生差异显著,但3年后生竹材差异不大;从基部到梢部竹材的气干密度、抗弯强度、抗弯弹性模量和顺纹抗压强度逐渐增加.综合考虑毛竹的物理力学性能和竹林的经济效益,适合采伐的是3年后生竹材,锯截之后的竹材也应根据部位不同进行区分,以便于加工应用过程中合理利用,提高产品的理化性能和质量的稳定性. 相似文献
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Strength grading of Norway spruce structural timber: revisiting property relationships used in EN 338 classification system 总被引：1，自引：0，他引：1
Solid timber for structural applications has to be strength graded prior to its use. In order to remain economic the grading process usually focuses on the most important physical and mechanical properties: density, modulus of elasticity (MOE) and bending strength. Based on respective limits given in standards, the timber is assigned to strength classes. Additional mechanical properties such as tensile and compression strength parallel to the grain are derived from the basic property values by empirical relationships. The objective of this study was to review some of these property relationships based on recently compiled large data sets as a contribution for a future revision of the grading standards. Based on mechanical tests of Norway spruce structural timber with different cross-sections, the following characteristic values and property relationships were evaluated: (a) strength and MOE in bending, (b) in-grade characteristic values of bending strength, bending MOE and density, (c) relationship of characteristic values of tension and compression strength parallel to the grain with respect to the corresponding characteristic value of bending strength, (d) ratio of fifth percentiles and mean values of density and MOE, as well as (e) the ratio of MOE in bending, tension and compression. Mechanical tests were accompanied by measurements of density and ultrasonic wave speed. Resulting dynamic MOE was partly used as an indicator of timber quality. 相似文献
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Kei Sawata Tatsuya Shibusawa Kazuo Ohashi Javier Ramon Sotomayor Castellanos Yasunori Hatano 《Journal of Wood Science》2008,54(1):45-53
Nail-head pull-through, lateral nail resistance, and single shear nailed joint tests were conducted on medium density fiberboard
(MDF) with different density profiles, and the relations between the results of these tests and the density profiles of MDF
were investigated. The maximum load of nail-head pull-through and the maximum load of nailed joints were little affected by
the density profile. However, the ultimate strength of lateral nail resistance, the stiffness, and the yield strength of nailed
joints were affected by the density profile of MDF and showed high values when the surface layer of the MDF had high density.
It is known that bending performance is also influenced by density profile. Therefore, the stiffness and the yield strength
of nailed joints were compared with the bending performance of MDF. The stiffness of nailed joints was positively correlated
with the modulus of elasticity (MOE); in the case of CN65 nails, the initial stiffness of joints changed little in response
to changes in MOE. The yield strength of nailed joints had a high positive correlation with the modulus of rupture (MOR).
The stiffness and the yield strength of nailed joints showed linear relationships with MOE and MOR, respectively. 相似文献
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Mikael Fonselius 《Wood Science and Technology》1997,31(6):399-413
Summary The effect of size on bending strength has been experimentally determined for laminated veneer lumber. Width was found to have no effect on bending strength. The effect of depth times length on bending strength obtained by the slope method was about 0.075, which is in good agreement with the results obtained by the shape parameter method. The effect of length is somewhat more severe than the effect of depth. Size was found to have no effect on modulus of elasticity or modulus of rigidity.In addition, the relationships between bending strength, modulus of elasticity and density of laminated veneer lumber were experimentally modelled.The author is pleased to acknowledge Research and Development Manager Matti Kairi, who represents the Kerto laminated veneer lumber manufacturer of Finnforest Oy, for fruitful co-operation over several years. The patience of senior research scientist Markku Kortesmaa, who calculated and several times explained the details of Appendix A for the author, is also acknowledged 相似文献
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为发展和科学利用速生阔叶工业用材种,对6种江西常见速生阔叶树木荷、苦楝、鹅掌楸、深山含笑、东京野茉莉及檫树的纤维形态及材性进行测定与分析。结果表明：木荷、苦楝、深山含笑、东京野茉莉的纤维都属长细型纤维,具有良好的制浆造纸性能,尤其苦楝属制浆造纸优等材,纤维长度最长,平均纤维长度达1.43 mm。檫树和鹅掌楸制浆造纸性能略差。11～12年生木荷和檫树密度已达中等密度木材范围,其中木荷平均密度最大,平均密度为0.69 g/cm3,但干缩性相对略大,深山含笑尺寸稳定性相对较好;木荷的综合强度最高,抗压强度50.52 MPa,属中级,抗弯强度和抗弯弹性模量分别为141.7 MPa、17.88 GPa,均属高等水平;鹅掌楸综合强度中等,顺纹抗压强度为50.52 MPa、抗弯强度84.99 MPa,抗弯弹性模量14.55 GPa;深山含笑抗弯强度和抗弯弹性模量均可达中等水平,但抗压强度略差;苦楝、东京野茉莉在材性综合强度方面稍差,抗压强度、抗弯强度和抗弯弹性模量方面均属低等水平。 相似文献
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The balance of strength between the flange and web parts of veneer strand flanged I-beam was investigated by the following
methods: (1) use of different web material types, such as plywood, oriented strand board (OSB), particleboard (PB), and medium
density fiberboard (MDF), that have different strength properties; and (2) fabrication of I-beams with low-density flanges
using low-density strands with PB web material. Replacing PB or MDF with plywood showed slight significant improvement in
the modulus of rupture but not in the modulus of elasticity of the entire I-beam. However, PB and MDF showed competent performance
in comparison with OSB, thus strengthening the promising future of the use of PB or MDF as web material to fabricate I-beams.
Hot-pressing conditions used for I-beam production exerted slightly adverse effects on the bending properties of PB, but not
on MDF, OSB, and plywood web materials. The flange density of 0.60 g/cm3 was considered to be the lower limit that provides I-beams with balanced mechanical properties and dimensional stability. 相似文献