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。     

原竹结构复合板的物理力学性能研究

以硬头黄竹为原料,根据竹材部位(基部、中部、顶部)和加工方式(两面加工、四面加工)的不同,压制原竹结构复合板并测定物理力学性能.结果表明:竹材部位对复合板的静曲强度、密度影响显著,对弹性模量、抗压强度、吸水厚度膨胀率有极显著影响；加工方式对复合板的静曲强度和吸水厚度膨胀率影响显著；两面加工原竹复合板的力学性能优于四面加工原竹复合板.     

单板层积材力学性能研究

经三种不同的外部条件处理后,使用无损检测设备(FFT)和力学试验机对杉木单板层积材试件静曲强度和弹性模量进行测量。结果表明,试件含水率在纤维饱和点以下时,无损检测方法(FFT)测得的弹性模量和力学试验机测得的静曲强度和弹性模量具有较优的线性相关性;在试件纤维饱和点以上,无损检测方法测得的弹性模量和力学测得的弹性模量有较优的线性相关性,而与静曲强度无线性相关性;单板层积材的静曲强度和弹性模量随着含水率的增加而降低。     

竹织物增强竹碎料板生产工艺研究

将竹材加工剩余物加工成一定规格形状的竹碎料,在竹碎料之间放置数层竹席组成板坯,然后热压成竹织物增强竹碎料板.该板材的静曲强度达到38.6 MPa,弹性模量2 908 MPa,内结合强度1.25 MPa,2 h吸水厚度膨胀率1.04%.该板材既使竹材加工剩余物得到充分利用,又克服了竹碎料板力学性能较差的缺陷.     

黄麻织物增强细木工板制备及其性能研究

以杉木板芯为芯层,桉木单板为面层,将连续的黄麻织物置于板芯和面层之间制备黄麻织物增强细木工板,研究黄麻织物的不同纱线密度对细木工板胶合性能和横向静曲强度的影响。结果表明,黄麻织物增强细木工板可行,3种纱线密度（30/10 cm、50/10 cm和80/10 cm）的黄麻织物增强细木工板的浸渍剥离性能合格率分别为100%、100%和83%;黄麻织物的纱线密度对细木板的静曲强度和弹性模量有影响,纱线密度为50/10 cm的黄麻织物增强细木工板的静曲强度和弹性模量最高,比未增强的细木工板分别提高约20%和30%。     

新型竹木复合板的研制

将竹材加工剩余物加工成一定规格形状的竹碎料,与木纤维均匀混合,按三层结构组成板坯,经热压胶合成一种竹木碎料/木纤维复合板材.经按GB/T17656-1999标准检测,该产品静曲强度达到31.5 MPa,弹性模量达到3041 MPa,均高于普通刨花板.     

断面密度分布与中密度纤维板力学性能关系的初步研究

通过改变热压曲线,热压出断面密度分布不同的板材并测量其静曲强度、内结合强度,进而分析平均密度、表层最高密度以及芯层密度与静曲强度、内结合强度的关系。结果表明：平均密度与板材力学性能之间的近似线性关系并不可靠;在一定的平均密度范围内,静曲强度与中密度纤维板表层最高密度呈近似的线性关系,内结合强度与中密度纤维板芯层密度呈相关性良好的线性关系。     

预压对中纤板静曲强度和弹性模量的影响

预压是中纤板高密度层生成的必要条件,高密度层对提高静曲强度有利,预压压力与静曲强度的提高成正比例关系;但对弹性模量的影响不大。     

白夹竹和寿竹制备竹基纤维复合材料初探

以白夹竹、寿竹不同疏解次数得到的单板为原料,对其压制竹基纤维复合材料的性能进行了研究。试验结果表明:疏解5~6遍竹材得到的单板压制的竹基纤维复合材料性能优良,板材的静曲强度均超过200 MPa、弹性模量超过20 000 MPa、垂直加载剪切强度超过20MPa、吸水厚度膨胀率小于10%、内结合强度大于3MPa,均能达到部分工业结构用材的要求。     

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。     

竹木复合集装箱底板表层材料的研制

根据复合材料层合板理论中表层材料力学性能越好对整个层合板的力学性能贡献越大的理论，用一定厚度的竹帘按照一定的组坯方式，采用正交设计方案对热压工艺进行优化，试验结果得出：用6层0．8mm厚的竹帘按照上面4层纵向竹帘和下面2层横向竹帘的组坯方式，在压力5MPa、时间8min、温度150℃的热压工艺下可以制成纵、横向弹性模量分别为13558MPa、5430Mpa，纵横向静曲强度分别为180MPa、110MPa的集装箱底板表层材料（竹帘板）。     

热压干燥对竹材密度和强度的影响

对热压干燥后龙竹竹材的密度和强度进行了测试和分析。结果表明:竹材热压干燥后,竹材试件表面密度增大,竹材厚度方向各部位密度趋于接近,竹材强度明显高于气干竹材试件强度,MOR和MOE分别较气干竹材增加了28.55%和29.44%。     

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 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.     

The influence of compression failure on the bending, impact bending and tensile strength of spruce wood and the evaluation of non-destructive methods for early detection

Bending strength (MOR) and bending Young’s modulus (MOE) according to DIN 52186 and MOE calculated on the basis of eigenfrequency and sound velocity were tested on small clear wood specimens of Norway spruce wood with and without compression failure. One group of specimens was climatised in a normal climate of 20°C and 65% relative humidity, while the other group was stored for one month under water before testing. The MOR of specimens with compression failure decreased about 20% on average (normal climate and wet) compared with the specimens without compression failure. The MOE of the specimens with compression failure was reduced only minimally compared with the specimens without compression failure stored in a normal climate, but very distinct differences (more then 30%) were found under wet conditions. The MOE of the specimens with compression failure calculated on the basis of eigenfrequency and sound velocity were not reduced or only minimally compared with the specimens without compression failure. It is therefore not possible to detect compression failure and to determine reduction in MOR using eigenfrequency or sound velocity. In addition, impact bending (DIN 52189), tensile strength and tensile MOE (DIN 52188) were tested on small clear wood specimens of Norway spruce wood with and without compression failure. The specimens with compression failure revealed an average reduction in impact strength of about 40% and an average reduction in tensile strength of about 20% compared with the specimens without compression failure, whereas tensile MOE of the specimens with compression failure was not reduced compared with the specimens without compression failure. The detection of compression failure by computer tomography (CT) was tested on Norway spruce wood boards 10 cm in thickness, and detection by optical scanner was tested on planed Norway spruce wood boards. CT recognised large compression failures easily, whereas the scanner was not able to detect them.     

竹篾层压板的力学性质及耐老化性能研究

利用靠近竹青和靠近竹黄的竹篾分别生产层压板,对其抗弯、抗压力学性质及其耐老化性能进行比较研究,为竹材的优化利用提供基础资料。研究结果表明:利用靠近竹青的竹篾制备的层压板的抗弯抗压力学性能远远高于利用靠近竹黄的竹篾制备的高低两种密度的层压板的性能。在实验室加速老化处理后利用靠近竹青的竹篾制备的层压板的抗弯弹性模量、抗弯强度和顺纹抗压强度的保留率都很高,表现出很强的抗老化能力;利用靠近竹黄的竹篾制备的层压板的顺纹抗压强度的保留率也比较高,而抗弯弹性模量、抗弯强度保留率较低,特别是利用靠近竹黄的竹篾制备的低密度层压板的抗弯强度保留率最低;利用靠近竹青的竹篾制备的层压板、利用靠近竹黄的竹篾制备的高密度层压板的厚度变化率都较高,而利用靠近竹黄的竹篾制备的低密度层压板的厚度变化率最低。本研究的结论表明:竹篾性能对层压板的性能有重要的影响,竹篾分类利用对于促进竹材的适材适用和高效利用具有一定的意义。     

The mechanical properties of densified VTC wood relevant for structural composites

The mechanical properties of densified wood relevant for structural composites were studied. Low density hybrid poplar (Populus deltoides × Populus trichocarpa) was densified using the viscoelastic thermal compression (VTC) process to three different degrees of densification (63, 98, and 132%). The modulus of rupture (MOR) and the modulus of elasticity (MOE) of the control (undensified) wood and of the VTC wood were determined. The bonding performance of the control and VTC wood, using two phenol-formaldehyde (PF) adhesives, was studied. Four different 3-layer composites were also prepared from undensified and VTC wood, and tested in four-point bending. The results showed that the bending properties of the VTC wood (MOR and MOE) were significantly improved due to the increased density. The bonding performance of VTC wood with PF adhesives was comparable with or better than in the case of the control wood. Increased density of the face layers in the 3-layer VTC composites was advantageous for their mechanical performance.     

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.