Critical discussion of perpendicular to grain tension testing of structural timber – case study on the European hardwoods ash,beech and maple

ABSTRACT

Knowledge about perpendicular to grain tension behavior of wood is essential, since in construction tension stresses perpendicular to grain cannot be avoided completely. Especially for hardwoods, the data basis is scarce. EN 338 design values are with 0.6 N/mm² characteristic strength set very low. The US-American National Design Specifications even set this value to zero and make local reinforcements mandatory. This paper compares strength and stiffness values attained with newly-designed, little, prismatic specimens and EN 408 structural timber specimens to evaluate the current European design values. Little specimen’s characteristic strength values range from 7.2 to 10.6?N/mm² and are assumed to be real material properties. EN 408 specimen values are with approximately 4.0?N/mm² lower. These lower values are mainly due to stress peaks introduced by the force introduction. Strength values attained for the medium-dense European hardwoods beech, ash and maple exceed EN 338 design values by a factor of six to seven. Adaptation of the EN 338 design value is not recommended, though. The abundance of influencing factors makes clear that the design value and the ensuing design code have to be synchronized carefully by tedious testing in order to make use of the perpendicular to grain tension strength potential of the selected hardwoods.     

Electronegativity Scale of Elements Calculated by Density Functional Theory and Related Methods

In chemistry and many related fields, electronegativity (EN) is an important fundamental concept and its scale is a useful physcochemical parameter. Here, calculations of both ionization potentials and electron affinities are extended toward 107 elements and done by density functional theory at the local density approximation(LDA) level and the LDB level, i.e., the local density approximation level with further non-local corrections for exchange and correlation included self-consistently as well as the modified Slater transition-state method. The definite-differentiation method is employed into calculations of the electronegativity scale and the related parameters of 107 elements with very good results due to the consideration of relativistic effects. The calculation presented is to examine both the LDA and LDB approximations in calculations for the ionization potential and electron affinity of the elements with an improved or modified Slater transition-state method, and relativistic effects have also been taken into account for 107 elements compared with 103, 86 or less in the previous report under a spin polarized density function theory with some approximations to the exchange-correlation function. The calculation results for the various quantities represent an obviously improvement over some previous calculations. It is shown that the results calculated by the extended technique and the improved Slater transition-state method in general agree well with experimental values presented by Pearson, and are better than the reported values in many previous literatures. The developed new electronegativity scale will widely be applicable in many fields such as molecular structural parameterization expression, chemobiological activity optimization prediction, structure-activity quantitation modeling, functional chemical adaptization designing, and so on.     

干扰素与免疫—神经—内分泌网络研究

干扰素是一组具有多种功能的免疫活性蛋白质，有抗病毒、抗肿瘤和免疫调节的作用。免疫－神经－内分泌网络中有许多活性物质，如神经递质、神经调质、激素和干扰素彼此相互作用，以调节机体生理功能，维持内环境的稳定，干扰素在网络中起一定作用。     

Evaluating durability of thermoplastic wood composites against basidiomycetes and development of a suitable test design

Abstract

Wood polymer composites (WPC) consist mainly of wood particles from non-durable softwoods. From experience in service life and laboratory testing it is known that WPC is not fully resistant against biological attack. Concerning durability testing, it is difficult to reach sufficient moisture content for fungal growth in the time frame of testing. Furthermore, the interpretation of test results is difficult, since the mass loss is measured but strength loss might be more important during service life. The relation between mass loss and strength loss is not deeply explored so far. Additionally moisture uptake causes an irreversible strength loss of WPC. Considering these problems a new test method for investigating the resistance of WPC against basidiomycetes is described in prEN 15534-1. In this paper, several test methods were carried out regarding their suitability for durability testing of WPC. The tests included various pre-wetting methods. After durability testing the mass loss and changes in strength and stiffness were evaluated. The results have shown that pre-wetting according to EN 84 is suitable to increase the moisture content. Furthermore strength and stiffness loss is higher than mass loss. The loss in mechanical properties is based on moisture uptake as well as fungal decay.     

山药收获机传动轴EN31合金钢车削过程中功率消耗及温度变化

以某山药收获机传动轴EN31合金钢为研究对象,利用瓦特表和红外线测温仪分别测量加工过程中机床功率消耗及工件加工最大温度,对不同主轴转速、进给量、切削深度深的车削过程进行实验分析。实验结果表明,随着主轴转速、进给速度和切削深度的增加,机床功率消耗、工件加工最大温度均呈上升趋势,上升趋势由明显变为平缓。     

碳氢化合物的气相色谱分析法——一种含脂类辐照食品的鉴别方法

介绍了欧洲标准EN1784—2003舍脂类辐照食品的鉴别——碳氢化舍物的气相色谱分析法的标准结构体系和主要内容．简述了该体系对我国相关技术的影响。     

3种竹材重组材耐老化性能比较

竹材重组材生产工艺简单、产品性能好、用途广,近年发展迅速。本文采用欧洲标准BSEN1087—1人工加速老化方法对冷压、热压、炭化热压三种工艺生产的竹材重组材进行了耐老化性能测试,并对测试数据进行分析、比较。结果表明：热压炭化竹材重组材老化前后的24h＊gt．水率、24h吸水厚度和宽度膨胀率均低于其他两种工艺生产的竹材重组材;热压炭化材与热压材耐老化处理后的弹性模量、静曲强度下降趋势和下降幅度差异不大,冷压材下降幅度最大;3种板材老化过程中内结合强度的变化情况差别不很明显,下降趋势和下降幅度基本一致。