Densification,screw holding strength,and Brinell hardness of European beech and poplar oriented strand boards

In this study, selected mechanical properties of beech and poplar oriented strand board such as screw holding strength (SH) and Brinell hardness (BH) as well as the relationship of stress and strain under compression for both species under two temperatures (180°C and 220°C) were examined. Poly methylene diphenyl diisocyanate resinated laboratory-scale boards in different design and density of both species (650 and 720?kg/m³) were prepared. The results showed that density has a positive effect on SH and BH of panels. It was also observed that wood species (beech or poplar) and size of strands (normal or fine size) also effect on SH. Both species showed a specific behavior regarding the lapse of stress and strain during compression.     

Effect of end connections on mid-span load capacity of laminated particleboard bookshelves

The purpose of the study was to determine the effect of joints on the mid-span load capacity of bookshelves made from laminated particleboard. Twenty types of joints were selected based on their popularity in the cabinet-making industry. Results showed that highest mid-span load capacities were obtained with glued groove joints that included glued wooden dowels. Overall, highest mid-span load capacities were obtained with fixed shelf-joint constructions, whereas lower capacities were obtained with adjustable constructions. Based on its high-load capacity and ease of construction, the spline joint appears best-suited for use by most craftsmen. Statistical lower tolerance limits were used to take capacity variability into account for design purposes. The 75% confidence|75% proportion limits for the glued wood spline and glued fiberboard spline joints were 94% and 93% of average, respectively.     

不同布根形式对草本植物根土复合体抗剪强度试验

为研究不同根系布置方式(方形、梅花形、环形)对草本植物根—土复合体抗剪强度影响,引入面积置换率的概念,解决了相同含根量或相同根数时无法同时满足方形、梅花形和环形布置的难题。在此基础上选取中国过渡带北侧山地土壤与莎草科植物开展植物根—土复合体抗剪强度试验研究,分析了相同布置形式下含根量对根—土复合体抗剪强度的影响、根系布置方式(方形、梅花形、环形)对草本植物根—土复合体抗剪强度增强作用以及抗剪强度指标变化规律。结果表明:根—土复合体试样的抗剪强度和黏聚力随着含根量的增大而逐渐增加;根—土复合体试样的内摩擦角随着含根量的增加变化不明显。根—土复合体试样的抗剪强度和黏聚力随着径级的增加而逐渐增大;根—土复合体内摩擦角与根系径级关系不大且规律性不明显。在法向应力较小时,根系的布置形式对根—土复合体的抗剪强度影响较小,当法向应力较大时,根系的布置形式对根—土复合体的抗剪强度影响不能忽略,且面积置换率越大,该误差越大。根—土面积置换率的较小时,方形布置的根系对黏聚力和内摩擦角影响最大,随着根—土面积置换率的增加,方形、梅花形及环形布置形式对根—土复合体黏聚力和内摩擦角的影响趋于稳定。     

基于离散元法植物根系对黏性土坡稳定性的影响

针对传统有限元方法不能够从细观尺度研究植被固坡作用的问题,采用离散元模型结合强度折减法,研究植被护坡位置对黏土边坡稳定性的影响。模拟结果表明:1)应用离散元模型结合强度折减法得到的无护坡情况下边坡安全系数为1.08,应用有限元模型得到的安全系数为1.09,表明采用离散元模型结合强度折减法分析边坡稳定是可行的;2)植被护坡位置对黏土边坡稳定性具有不同程度的影响:仅在坡面、坡脚或者坡顶种植植被时,植被对边坡的稳定性影响很小;3)当在坡面与坡脚或者坡顶与坡底都种植植被时,植被对边坡的稳定性具有较大影响,且当在坡顶、坡面和坡底全都种植植被时,对边坡稳定性的影响最大,边坡稳定性最高。研究结果为实际工程中植被护坡铺设位置的选择提供了相应的理论依据。     

Predicting dynamic modulus of elasticity of Norway spruce structural timber by forest inventory,airborne laser scanning and harvester-derived data

Norway spruce structural timber is one of the most important products of the Norwegian sawmilling industry, and a high grade-yield of structural timber is therefore important for the economic yield. Presorting of logs suited for production of structural timber might be one option to increase the grade yield. In this study, dynamic modulus of elasticity (E_dyn) of structural timber was predicted based on forest inventory data at site level and single-tree data from airborne laser scanning (ALS) and harvester. The models were based on 611 boards from 4 sites in southeastern Norway. Important variables at site level were elevation, site index (SI), and mean stand age. However, when combining data from all information sources, mean stand age and site index were the only significant variables at site level. Tree height and variables describing the crown, like crown length and crown volume, were important vaiables extracted from ALS data. Stem diameter measures and tapering were important variables measured by the harvester. The combined model with variables from all three information sources reduced the variance the most, especially when using individual tree age instead of average stand age. However, combining all these data requires accurate positioning of the trees by the harvester.     

秸秆湿贮存过程添加剂协同调控对甲烷产量的影响

以干黄玉米秸秆为原料,研究可溶性糖(葡萄糖)及其与同型乳酸菌、异型乳酸菌、乙酸协同添加对原料湿贮存过程中品质及甲烷产量的影响。结果表明:单一葡萄糖添加组,贮存30 d,干物质损失率为4.7%,以乳杆菌属、片球菌属、肠球菌多种乳酸菌主导,乳酸与乙酸含量(干基质量比)分别为36 g/kg和5 g/kg,秸秆产甲烷潜力比空白组提高6.8%;葡萄糖植物乳杆菌协同(同型发酵)组,贮存30 d,干物质损失率为4.6%,乳酸含量升高至62 g/kg;葡萄糖短乳杆菌协同(异型发酵)组,贮存30 d,干物质损失率为5.5%,乳酸与乙酸含量分别达到44 g/kg和12 g/kg;两类乳酸菌的协同添加均未对产气潜力产生进一步促进作用;葡萄糖乙酸协同组,贮存30 d,干物质损失率为3.6%,乳酸与乙酸含量分别升高至75 g/kg和20 g/kg,异型乳酸发酵魏斯氏菌属丰度升高至16.87%,有效抑制肠杆菌属(腐败菌)生长,秸秆产甲烷潜力提高8.7%。综合分析本试验结果,当原料可溶性糖含量不足时,外源糖的补充是保证原料高效贮存及产气的关键,协同乙酸添加可强化以魏斯氏菌属为主导的异型发酵过程抑制腐败菌生长,强化贮存过程的稳定性。     

有害疣孢霉与不同食用菌的培养关系

【目的】研究有害疣孢霉与不同食用菌的培养关系,为蘑菇疣孢霉病害诊断及其致病机理研究提供参考依据。【方法】采用形态观察及PCR方法,对供试的疑似有害疣孢霉菌株进行鉴定。采用接种法,研究有害疣孢霉对食用菌的致病力及其发酵滤液对食用菌菌丝体生长的影响,并分析食用菌菌丝体发酵滤液及其子实体煎汁对有害疣孢霉生长的影响。【结果】鉴定结果表明,本研究供试的病原菌为有害疣孢霉。有害疣孢霉能侵染金针菇、糙皮侧耳、双孢蘑菇、金顶侧耳、刺芹侧耳,不能侵染香菇;其中有害疣孢霉对糙皮侧耳、金顶侧耳、双孢蘑菇及金针菇的致病力强,对刺芹侧耳的致病力弱。糙皮侧耳、双孢蘑菇、刺芹侧耳、灵芝、香菇子实体煎汁和菌丝体发酵液均能促进有害疣孢霉菌丝体的生长;灵芝的子实体浸汁和发酵液均能抑制有害疣孢霉厚垣孢子的产生。有害疣孢霉发酵滤液能够促进供试食用菌菌丝的生长。【结论】有害疣孢霉对不同食用菌的致病力有一定差异,灵芝对有害疣孢霉厚垣孢子的产生具有较强的抑制作用。     

太湖平原地区不同土地利用类型对水质的影响

为探讨不同土地利用类型对太湖流域水质状况的影响,以太湖腹部平原区为例,基于典型年地表河流水质监测数据,结合TM影像解译结果所反映的土地利用状况,分别从区域和水质站点周边缓冲区两个方面,计算不同土地利用类型与水质状况的灰色关联序,以反映土地利用类型对地表水质的影响,为太湖腹部平原区的土地利用与水污染防治提供参考。结果表明:河流水质整体上与土地利用类型的灰色关联度最大的是城镇用地,其次是水田和旱地,水域和林地的灰色关联度最低;丰水期、枯水期的不同水质指标与土地利用的灰色关联序有一定区别,而水质站点缓冲区土地利用为样本时,水质指标受城镇用地影响最大,其次为耕作用地,最低为水域。     

荸荠压缩特性试验研究

为获得荸荠的力学性能参数及对荸荠破坏极限的影响,以荸荠的品种、压缩速率及压缩部位为试验因素,对荸荠进行正交压缩试验。通过分析其对应的力-位移曲线所得到相应的破坏极限Fb、破坏能Ub等参数的试验,得出结果表明,在相同变形的情况下,荸荠轴向所承受的载荷大于径向载荷。方差分析发现,荸荠品种、压缩部位以及荸荠品种和压缩部位之间的交互作用对破坏极限影响极显著,压缩速率对破坏极限影响显著,而荸荠品种与压缩速率之间的交互作用对破坏极限影响不显著。     

毛竹材性差异对胶合竹层板应力分级的影响

通过测试不同杆高部位毛竹竹材的密度、抗弯强度及弹性模量,采用不同杆高部位的竹条制备胶合竹层板,并以抗弯弹性模量为指标对其进行分级,初步研究了不同杆高部位材性的差异对胶合竹层板分级的影响。结果表明,毛竹气干密度从基部至梢部呈现增大趋势,杆高3~9 m处密度增大趋势较缓,气干密度值相近。毛竹抗弯强度及弹性模量从基部至梢部呈现增大趋势,梢部性能最优,其中杆高1~5 m部位竹材性能接近,杆高5~9 m部位性能接近;胶合竹层板E-Rated级别与竹材抗弯强度及弹性模量密切相关,相对应E-Rated级别由低到高大致可分为4级。