单板含水率与桉木单板层积材性能关系初探

对不同含水率桉木单板压制的单板层积材的静曲强度、弹性模量和水平剪切强度进行检测并对比分析,结果表明,结构用单板层积材所用单板的含水率应控制在8%～12%之间。     

增强型层积材地板力学性能分析

采用玻璃纤维布和碳纤维布层间增强单板层积材地板。研究了玻璃纤维布和碳纤维布铺设位置对增强型层积材地板力学性能的影响;设计正交试验,研究了涂胶量、热压温度、热压压力、热压时间对增强型层积材地板力学性能的影响,并得到较优工艺参数。结果表明:玻璃/碳纤维布对称铺设时,靠近单板层积材地板表层铺设时对静曲强度和弹性模量的增强效果较在中间层铺设时的增强效果明显;分析可得层间增强单板层积材地板的工艺较优参数为:涂胶量160g/m2,热压温度110℃,热压压力1.2MPa,热压时间100s/mm;通过方差分析可得,只有热压压力对弹性模量影响显著,其他因素对静曲强度和弹性模量影响都不显著。     

单板层积材力学性能的研究

介绍单板层积材几种力学性能的检测方法及其试验结果的对比,发现在不同跨距和加荷数量情况下,两种检测方法测得的静曲强度和弹性模量结果差异不显著。对比水平剪切强度、拉伸剪切强度和压缩剪切强度显示三者之间相关性不好,压缩剪切强度值标准差(1.92)远大于水平剪切(0.51)和拉伸剪切(0.90),压缩剪切值具有较大的试验误差,但是统计发现三种剪切强度试验结果均服从正态分布。     

单板层积材力学性能的研究

介绍单板层积材几种力学性能的检测方法及其试验结果的对比，发现在不同跨距和加荷数量情况下，两种检测方法测得的静曲强度和弹性模量结果差异不显著。对比水平剪切强度、拉伸剪切强度和压缩剪切强度显示三者之间相关性不好，压缩剪切强度值标准差(1．92)远大于水平剪切(0．51)和拉伸剪切(0．90)，压缩剪切值具有较大的试验误差，但是统计发现三种剪切强度试验结果均服从正态分布。     

酚醛树脂桉木单板层积材生产工艺研究

探讨利用酚醛树脂胶黏剂压制桉木单板层积材的工艺,分析了热压温度、热压时间和面粉添加量对桉木单板层积材力学性能的影响。研究表明：面粉添加量对桉木单板层积材的静曲强度和弹性模量有显著影响,而热压温度和热压时间的影响则不显著。就产品力学强度而言,较佳的工艺条件为：热压温度135℃,热压时间1.2 min/mm,面粉添加量0。验证试验证明,在实际生产中,综合生产成本及产品性能等多方面考虑,添加15%的面粉是可行的。     

纤维板的弹性模量及静曲强度的动态检测

利用振动无损检测法测得纤维板的动态弹性模量,并用一元和二元回归分析了纤维板的密度、静态弹性模量、动态弹性模量、静曲强度之间的相关性。结果表明:纤维板的静态弹性模量与动态弹性模量之间,或动态弹性模量与静曲强度之间均密切线性相关;以纤维板的动态弹性模量和密度为自变量与静曲强度建立二元回归方程,其相关程度较一元回归更为密切。密度及长度与横截面面积比值较大的纤维板,其动态弹性模量与静态值更为接近。     

用于纤维质小尺寸材料力学性能测试的试验机研制

根据纤维质小尺寸试样的静曲强度和抗弯弹性模量的测试要求,利用弹性构件的胡克定律,试制了一种简易的实验用力学测试装置。从利用该样机测试马尾松的抗弯弹性模量和静曲强度的数据来看,这种测试装置用于测试小尺寸试样的静曲强度和抗弯弹性模量是可行的,试验机通过进一步完善和有关元件的配套,完全可以在小尺寸材料力学性能测试中使用。     

基于单片机的单板层积材抗弯强度应力波波速检测系统

介绍了一种自主开发的单板层积材应力波弹性模量检测系统.该系统以单片机为数据处理核心,通过在线检测应力波的波速及相关参数来计算单板层积材的动态弹性模量和抗弯强度,进而实现单板层积材强度的分等.文中讨论了系统的检测原理,给出了具体的硬件实现电路、软件设计,并对系统进行了实验验证.     

酚醛树脂浸渍杨木单板层积材防腐及力学性能研究

为了拓展人工林杨木在户外的应用,制备了酚醛树脂(PF)浸渍杨木单板层积材(LVL),并对其微观结构、耐腐性能和力学性能进行分析。结果表明,低分子量酚醛树脂能够进入杨木单板的导管和纤维中的空隙;浸有酚醛树脂的杨木单板层积材表现出优异的防腐性能,且抗弯强度和弹性模量分别提高了6.91%和71.11%。     

柔性垫网接触式干燥中单板干燥速度变化规律的研究

本文介绍了在柔性垫网接触式干燥中单板干燥速度的变化规律及温度和初含水率对干燥速度的影响。单板干燥分为预热、快速干燥、减速干燥和慢速干燥四个阶段。温度越高干燥速度越快 ,但温度超过160℃后提高幅度减小 ,所以160℃为适宜温度。初含水率不同的单板在纤维饱和点前后干燥速度的变化趋势相反。初含水率越高的单板 ,在纤维饱和点之前的干燥速度越快 ,在纤维饱和点之后越慢     

Effect of laminated structure design on the mechanical properties of bamboo-wood hybrid laminated veneer lumber

The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a one-piece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (B-bamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.     

Comparison of European standard EN 310 and EN 789 in determining the bending strength and modulus of elasticity of red seraya (Shorea spp.) plywood panel: experimental and finite element analysis

The characteristic bending strength (MOR) and mean modulus of elasticity (MOE) of red seraya (Shorea spp.) plywood was determined using European Standard bending tests EN 310 and EN 789. The experiment found that the MOR of EN310 was higher whereas MOE were lower than those obtained from EN 789. The study also found that the choice of wood species influenced the correlation of MOR and MOE obtained by EN 310 and EN 789. Finite element (FE) model was proposed to predict MOR and MOE values. The FE analysis method showed satisfactory agreement with the experimental results, especially for EN 789. The R² values for EN 789 attempted through linear regressions range from 0.96 to 0.99. Nevertheless, it was noted that the FE models in this study had put some limitations on the prediction.     

Swelling restraint of thermally modified ash wood perpendicular to the grain

The paper reports on creep of ash wood (Fraxinus excelsior L.) thermally modified at 180 and 200 °C, and subsequently subjected to compression in tangential and radial directions and simultaneously wetted, from the moisture content (MC) of 6% to above the fibre saturation point (FSP). The compressing load made 0.00, 0.25, 0.50 and 0.75 of impact stress at the proportional limit (R_c). The compression stress needed to restrain the swelling of wood, the so-called swelling pressure, was indirectly determined from isochrones of mechano-sorptive creep. The most important finding was that thermal modification reduces the strain of ash wood subjected to compression perpendicular to the grain to a degree proportional to the mass loss. The compression stress needed to restrain the swelling of thermally modified wood is ca. 10 and 20% smaller in the tangential and radial directions, respectively. This effect leads to a reduction in the anisotropy of swelling pressure of thermally modified wood perpendicular to the grain. Moreover, although upon thermal modification the mass loss of wood takes place, at the MC of 6% it shows practically the same modulus of elasticity (MOE) and Rc as the unmodified wood. After wetting to MC higher than the FSP, the thermally modified wood at 200 °C shows significantly higher MOE and Rc than the wood modified at 180 °C and untreated wood. Reduction of wood hygroscopicity, an inevitable effect of thermal modification, also reduces the range of changes in mechanical properties of wood caused by the increase in its MC to the FSP.     

Bending properties of a novel engineered composite from southern pine lumber

This paper presents the results of a study in which novel engineered composite lumber was developed, manufactured and tested. The engineered composite lumber was made by edge-laminating lower-grade No. 3 solid-sawn southern pine (SP) lumber with higher-grade tension chord material to yield tension chord lumber (TCL). Three groups of TCL (38 mm × 235 mm × 4.9 m) were made with varying combinations of SP lumber including machine stress rated (MSR) 2400Fb-2.0E, MSR 2400Fb-2.0E finger joint, and visually graded No. 1 finger joint material. One group of visually graded No. 3 control lumber (38 mm × 184 mm × 4.9 m) was also tested. All specimens were tested in static four-point bending on a universal testing machine. The modulus of elasticity (MOE) and modulus of rupture (MOR) were determined. The TCL lumber had significantly greater MOE values as compared with the control lumber. The mean MOE values of TCL ranged from 12.4 to 12.6 GPa, as compared with 9.6 GPa for the control group. The mean MOR values of TCL ranged from 39.3 to 47.6 MPa, as compared with 35.9 MPa for the control group. Perhaps most importantly, the 5th percentile values of MOR of the TCL were approximately double those of the control group, 29.1, 27.0, and 27.4 MPa versus 11.8 MPa, respectively.     

An empirical model for predicting the mechanical properties degradation of bamboo bundle laminated veneer lumber (BLVL) by hygrothermal aging treatment

An empirical 3-D model was developed to evaluate the effect of ambient environment on the mechanical properties and degradation behavior of bamboo-bundle laminated veneer lumber (BLVL) fabricated with different levels of PF/PVAc resin. This model can describe the relationship between the modulus of elasticity (MOE), water absorption ratio, and aging temperature. Five levels of PF/PVAc weight ratio (2:1, 4:1, 6:1, 8:1 and 10:1) and three treatment conditions (18, 63, and 100 °C) were examined in this experiment. Computed tomography (CT) scanning technology was employed to observe the morphology of damage degree as well as explore the mechanism of degradation behavior of BLVL. The results indicated that the 3-D model used for tracking and monitoring the variance of MOE provided good predictors. The higher the water impregnation temperature the larger the water absorption ratio and the higher the MOE degradation were. The aging temperature had a significant effect on the mechanical properties and degradation behavior of BLVL. A linear relationship between modulus of rupture (MOR) degradation and aging temperature was observed. The degradation rate of MOE and MOR increased as the temperature increased. The aging degree tested by CT along with damage of inner board showed the PF/PVAc ratio had a significant influence on the mechanical degradation of treated BLVL when the PF/PVAc ratio was below 6:1. Localized yielding, micro-cracks developing between interfaces, PVAc resin softening along with delamination, and debonding were the main failure models for the BLVL by hygrothermal aging treatment.     

Density and some mechanical properties of densified and heat post-treated Uludağ fir,linden and black poplar woods

The effects of thermo-mechanical densification and heat post-treatment on air-dry density, modulus of elasticity (MOE), bending strength (MOR), and compression strength parallel to the grain (CS) of Uluda? fir (Abies bornmulleriana Mattf.), linden (Tiliagrandifolia Ehrh.), and black poplar (Populus nigra L.) wood samples were investigated. Samples were densified with compression ratios of 25 and 50%, and at 100 and 140?°C. Then, the heat treatment was applied to the samples at 185 and 212?°C for 2 h. According to the results of the study, density of all wood samples increased together with the increase of compression ratio. Regarding compression temperature, the highest density increase was obtained at 100?°C. Mechanical strength (MOE, MOR, and CS) in densified samples increased depending on compression ratio and increase of density. The highest strength increase was in black poplar samples and the lowest was in linden samples. After heat post-treatment, mechanical strength of samples decreased depending on increase in treatment temperature. However, strength values (MOR except) of samples which are 50% compressed and heat-treated were found higher than control samples.     

Effect of panel properties on the concentrated static load (CSL) performance of oriented strand board (OSB)

The relationship between concentrated static load (CSL) performance of oriented strand board (OSB) and panel thickness, local density, and some mechanical properties (including modulus of elasticity (MOE), modulus of rupture (MOR), and interlaminar shear strength in both major and minor directions) was investigated using both a simple linear regression method and a stepwise multi-linear regression technique. The sample boards were laboratory manufactured OSB panels consisting of eighteen combinations of different strand geometries (length, width, and thickness), strand orientations, and fines contents. Simple linear regression analysis showed that MOE (major direction), MOR (major direction), shear strength (major direction), local thickness, average board density and local density were all significantly and negatively correlated with the CSL deflection; however, in the stepwise multi-linear regression analysis only MOE (major) and local thickness were retained as significant factors possibly due to inter-correlation amongst the variables. Shear strength (major direction), MOR (major direction), average board density, MOE (major direction), MOR (minor direction), local thickness, average board thickness, local density, and shear strength (minor direction) were all found to be significantly and positively correlated with the CSL ultimate load in the simple regression analyses, but only shear strength (major) and local panel thickness were retained in the stepwise multi-linear regression model for the CSL ultimate load.     

Mechanical properties of wood treated with PF-pyrolytic oil resins

Jack pine and sugar maple wood samples were treated in a two-step process that involved first a copper chloride or a copper chloride-sodium borate mixture and then a phenol-formaldehyde resin containing a certain percentage of softwood bark pyrolytic oil. Various controls were also prepared for comparison. The modulus of rupture (MOR) of jack pine samples was generally negatively affected by the treatment, the observed values being lower than those of the controls. These values were statistically lower or equal to those of untreated samples. On the other hand, the modulus of elasticity (MOE) of treated jack pine samples was not found to be statistically different from that of the untreated wood. Mechanical properties behaved in a similar way for sugar maple wood. Unlike the other treatments, copper chloride–sodium borate and the resin containing 85% of pyrolytic oil as phenol substitute appeared to slightly improve the mechanical properties of both wood species even if not significantly so. Treatment with PF-pyrolytic oil resin resulted in similar or slightly better mechanical properties when compared to CCA-treated wood. The amount of treating water soluble salts retained in samples after the first treatment had a significant impact on MOR of both wood species and on MOE of sugar maple.     

Comparison between heat treated sapwood and heartwood from Pinus pinaster

Sapwood and heartwood samples of Pinus pinaster were treated in an oven at 190 and 200 °C for 2–6 h. Dimensional stability, measured as Anti Shrinking Efficiency (ASE) between 0 and 65 % relative humidity, durability against fungi, mechanical resistance (MOE and MOR), hardness and chemical composition were determined for treated and untreated sapwood and heartwood. Radial ASE reached 52 % for sapwood and 50 % for heartwood, while tangential ASE reached 50 and 40 %, respectively. MOE increased slightly at the beginning of the treatment, decreasing afterwards. No significant differences were found between sapwood and heartwood. MOR decreased by 50 and 30 % for sapwood and heartwood, respectively. A significant increase in durability against Rhodonia placenta was found for both heartwood and sapwood at the higher temperature (200 °C), but at the lower temperature (190 °C) only heartwood showed good results.