单板机在气轨实验的在线时间测量

在气轨实验中，采用Z80单板机设计单板数字毫秒仪，精确测量在线时间。     

Effects of thermo-hygro-mechanical densification on the surface characteristics of trembling aspen and hybrid poplar wood veneers

The effect of thermo-hygro-mechanical (THM) densification temperature on the surface color, roughness, wettability, and chemical composition of trembling aspen (Populus tremuloides) and hybrid poplar (Populus maximowiczii × P. balsamifera) veneers was investigated. Veneers were subjected to four THM densification temperatures (160 °C, 180 °C, 200 °C, and 220 °C). Veneer color darkened with increasing THM densification temperature. Surface roughness decreased between 160 °C and 200 °C. Wettability decreased after THM densification, but no significant difference was found between treated specimens. ATR-FTIR and XPS results confirmed that THM densification caused major chemical changes in veneer surfaces, and more pronounced at temperatures higher than 160 °C.     

化学镀铜天然高分子材料表面特征的近红外光谱分析

通过对天然高分子材料木材进行化学镀的方法制成的木质电磁屏蔽材料既可以保留木材的一些优良特性,又能有效改善木材导电、 导热和电磁屏蔽性,不仅为木材的增值利用开辟了新道路,还为电磁屏蔽材料的加工利用拓宽了领域。本研究利用近红外光谱结合主成分分析法对化学镀铜处理前后样品进行了分析研究,旨在探讨利用近红外光谱技术研究该材料表面特性的可行性。结果表明：(1)化学镀铜前后样品表面的近红外光谱在形状和吸收强度上存在显著差异,而不同镀铜时间的样品之间也存在差异,尤其是反应未充分的样品。(2)经过主成分分析后,镀铜前后样品沿PC1轴、 PC2轴大致分成了6类,其中未处理样品、 活化处理样品性质较接近,镀铜时间25和40 min样品因反应充分,性质也比较类似,说明近红外光谱中包含反映材料处理前后的重要特征信息。(3)比较近红外区域和可见光区域光谱的主成分分析效果,发现近红外光谱区比可见光光谱区对镀铜处理前后样品的分类效果好,可见光光谱在突出样品的表面颜色特征信息方面表现更好,这说明两者结合运用更有利于样品表面特征信息的表征。     

Formation of Saddle-Shaped Composite Sheets

Based on the deformation model of an unbalanced multilayer composite, changes in bending curvatures of sheet-type composites with nonsymmetric structure relative to the midplane of the sheet, depending on the moisture of layers, are predicted. The bending curvatures of saddle-shaped sheets of wood-based composites are calculated with regard to the physical and mechanical properties, geometrical dimensions, orientation, and distribution of layers. The analytical results are compared with the bending curvatures found experimentally for a four-layered unbalanced composite made of birch veneer. The applied calculation model enables us to determine the values of bending curvatures of saddle-shaped wood composite sheets, which can be used in elaborating the technological recommendations.     

钢-LVL组合工字形梁受剪性能研究

将单板层积材(LVL)和冷弯薄壁型钢通过结构胶复合形成工字形截面的组合梁,以组合梁的剪跨比、腹板和翼缘LVL厚度为参数,对9根钢-LVL组合工字形梁进行受剪性能试验,观察其在不同荷载作用下的破坏现象、破坏形态、应力变化及挠度的发展,对受剪承载力的影响因素进行分析,并提出组合梁的跨中挠度及受剪承载力的计算方法.试验结果表明,钢-LVL组合工字形梁的整体工作性能较好,组合效应显著,其受剪承载力与剪跨比、腹板厚度及翼缘厚度有关.当剪跨比小于2.5时,试件表现为明显的剪压破坏,腹板厚度、翼缘厚度的增加以及剪跨比的减小,可以有效地提高其极限受剪承载力.提出了组合梁的跨中挠度和受剪承载力计算模型,与试验结果吻合良好,实测挠度与计算挠度误差在8%以内,受剪承载力试验值与计算值平均误差不超过10%.     

Electroless nickel plating on APTHS modified wood veneer for EMI shielding

A new activation process was developed for electroless plating to prepare wood-based EMI shielding material. Pd(II) was adsorbed on a wood surface modified with γ-aminopropyltrihydroxysilane (APTHS) formed by the hydrolysis of γ-aminopropyltriethoxysilane (APTES). After reduction of Pd(II), electroless plating was successfully initiated and an Ni-P coating was deposited on the wood veneer. The activation process and resulting coating were characterized by XPS, SEM-EDS and XRD. The metal deposition, surface resistivity and electromagnetic shielding effectiveness were measured. XPS analysis proved that Pd(II) was bonded to the amino group of APTHS and was reduced to Pd(0). The Ni-P coating was uniform, compact and continuous, and consisted of 3.39 wt.% phosphorus and 96.61 wt.% nickel. XRD analysis indicated that the coating was crystalline, which is thought to be related to the low phosphorus content. The plated birch veneers exhibited electromagnetic shielding effectiveness greater than 60 dB in the frequency range 10 MHz-1.5 GHz.