落叶松锯材抗弯强度尺寸效应

以兴安落叶松锯材为研究对象,研究了不同目测等级下锯材尺寸与其抗弯强度之间的关系。试验选取1961根6.5、9.0和14.0cm 3种宽度尺寸的目测等级锯材,每个宽度尺寸分为高、低目测等级组,按照每组试件宽度18倍的测试跨度测试锯材的抗弯强度。利用斜率法和形状参数法确定高、低目测等级组抗弯强度5%分位值的长度与宽度的组合尺寸效应。研究结果表明,斜率法获得高、低目测等级组试件抗弯强度5%分位值的组合尺寸效应分别为0.19和0.23。     

Stretch rate and deformation for pre-stretching aluminum alloy sheet

Numerical simulation combined with experimental test was carried out to analyze the pre-stretching process of the 7075 aluminum alloy sheet, from which the stress variation curves and residual stress of aluminum alloy sheet in different stretch rates were obtained. The results show that the residual stress in length direction is released after unloading the stretch force, while the residual stress in width direction is released during the stretching process. The study of residual stress elimination is beneficial for optimizing stretch rate on the basis of residual stress distribution law. By comparing the variation principle of residual stress in length direction, the size range of three deformation areas and elimination percentage of residual stress were obtained. The residual stresses of clamping area and transition area are not eliminated effectively, so sawing quantity should be the sum of both the areas. The elimination rate of residual stress in even deformation area could reach 90% after choosing a proper stretch rate, which is verified by both simulation and experiment.     

Low temperature J-resistance curve determination of asphalt concrete using wavelet-Radon transform

A single specimen test using the three point single edge notched beam configuration at low temperatures for obtaining hot mix asphalt （HMA） resistance curves is developed.Resistance curves are obtained for mixtures at six temperature levels of＋5,0,-5,-10,-15,and-20 ℃ and three binder contents of 4％,4.5％,and 5％.Crack extension increments during the test are measured by means of an image processing technique using Radon transform and feature extraction.All the specimens exhibit a rising R-curve,indicating ductility and toughening mechanisms in the ductile-quasi brittle fracture of the mixture.It is observed that the reduction of temperature results in a further tendency of the mixture for unstable crack growth and less subcritical crack length.It is also shown that using the binarization process,an automatic index can be developed that can represent the extent of brittleness and extent of the low temperature in which the cracking has occurred.     

Bending stress of rolling element in elastic composite cylindrical roller bearing

A new structure design method of elastic composite cylindrical roller bearing is proposed, in which PTFE is embedded into a hollow cylindrical rolling element, according to the principle of creative combinations and through innovation research on cylindrical roller bearing structure. In order to systematically investigate the inner wall bending stress of the rolling element in elastic composite cylindrical roller bearing, finite element analysis on different elastic composite cylindrical rolling elements was conducted. The results show that, the bending stress of the elastic composite cylindrical rolling increases along with the increase of hollowness with the same filling material. The bending stress of the elastic composite cylindrical rolling element decreases along with the increase of the elasticity modulus of the material under the same physical dimension. Under the same load, on hollow cylindrical rolling element, the maximum bending-tensile stress values of the elastic composite cylindrical rolling element after material filling at 0° and 180° are 8.2% and 9.5%, respectively, lower than those of the deep cavity hollow cylindrical rolling element. In addition, the maximum bending-compressive stress value at 90° is decreased by 6.1%.     

具有弯拱度羽毛片的特性及其应用

主要研究具有弯拱度羽毛片的特性以及建立其转动惯量求解数学模型,通过测量羽毛片的羽毛叶和羽毛杆等相关数据得到了羽毛片质量分布与长度对应关系图.然后考虑羽毛片的弯拱度对其转动惯量的影响,并给出不同弯拱度类型时对应羽毛片质量分布图,从而得到了具有弯拱度的羽毛片转动惯量计算公式.最后根据转动惯量平行轴定理得到了以羽毛球对称中心点为坐标系的各转动轴的羽毛片转动惯量.仿真结果也进一步说明了不同类型弯拱度变化对羽毛片转动惯量的影响.对具有弯拱度羽毛片特性的研究,具有一定的实用意义.     

熔融法制备金矿尾砂微晶玻璃及性能测试

以金矿尾砂、方解石为主要原料,添加其它所需原料为硼砂、ZnO、Cr2O3、Sb2O3等,采用熔融法制备CaO-Al2O3-SiO2系微晶玻璃.利用硅碳棒炉在1 300℃~1 350℃下保温4h熔制玻璃,熔好的玻璃液浇注在事先预热的不锈钢模具上,成形后放入马弗炉在600℃保温1h退火处理,对玻璃试样热处理得到微晶玻璃样品.采用TG-DSC差热分析仪测定基础玻璃的DSC曲线,确定金矿尾砂微晶玻璃较佳的热处理工艺为:800℃保温2h进行核化处理,890℃保温3h进行晶化处理.通过XRD、SEM等分析手段对试样的物相及微观结构进行了分析,测定制得微晶玻璃的抗折强度、热膨胀系数、体积密度等性能.结果表明:制得金矿尾砂微晶玻璃的主晶相为:辉石和透辉石固溶体,样品的热膨胀系数为69.5×10-7/℃,抗折强度为119.2MPa,体积密度为2.81g/cm3.     

中美规范公路混凝土桥梁设计的分析与比较

由于重载汽车的增加以及目前桥梁的损坏状况日趋严重,为确保公路桥梁设计的安全使用,将中美两国公路桥梁混凝土规范的设计荷载及结构抗力计算进行比较,为我国公路桥梁设计提供参考。     

LFP-941D线路保护重合闸问题浅析

通过对一次线路保护传动时保护装置不发重合闸脉冲的问题进行分析,论述了保护装置启动展宽及重合闸脉冲在延时上的配合问题。