齿厚极限偏差与公法线极限偏差的图解法

《渐开线圆柱齿轮精度》(JB179-83)对齿轮副侧隙作了新规定,采用“基中心距”制,即固定中心距极限偏差,改变齿厚,以满足不同的侧隙要求,因此,中心距和齿厚极限偏差为其主要参数。 齿厚偏差△E,是在分度圆柱面上,齿厚的实际值S′与公称值S之差,即: △E=S′-S按照定义,齿厚是以分度圆弧长计值(弧齿厚),但在实际检测时,是以顶圆定位,测得分度圆弦齿厚,如图1所示,其合格性条件为: E_(SS)≥△E_S≥E_(Si)(△E_S=S′- S) 式中:E_(ss)-齿厚上极限偏差; E_(si)-齿厚下极限偏差; △E_s-齿厚偏差;S′-分度圆实际弦齿厚;     

热压条件对薄片刨花板厚度方向上膨胀分布的影响

传统的降低板材厚度膨胀的方法主要是通过提高施胶量和添加石蜡，或通过热、蒸汽、化学处理等，但往往会增加成本及影响材料的力学性能。板材厚度膨胀的最主要根源是木材的结构和特性以及热压时水分、温度、压力和时间对板材的综合作用。笔研究了在不同的热压条件下，板坯内不同层的薄片刨花的膨胀以及薄片刨花板厚度方向上的膨胀分布。结果表明，在较低的热压温度下，刨花的压缩率和膨胀率呈明显的相关性，而在较高的热压温度下，尽管表层刨花的压缩率较高，但其厚度膨胀率仍小于芯层刨花。为降低木质复合材料的厚度膨胀，建议采用较高的热压温度。     

季节性寒区隧道保温隔热层厚度计算方法

为了解决冻结锋面移动带来的保温层厚度不足的问题,以河北延崇高速棋盘梁隧道为研究对象,采用现场监测、数值模拟以及理论分析等方法对季节性寒区隧道冻结锋面的移动规律进行探究,得出考虑冻结锋面移动规律的保温隔热层计算公式。结果表明：在同一断面内,较厚的仰拱填充对温度的传递起到一定的阻碍作用,冻结锋面在拱顶处的深度大于边墙处的深度。随着时间的推移,冻融循环的反复进行,季节性寒区隧道的冻结锋面深度会逐渐加深,最终趋近于一稳定值。不同断面的冻结锋面最终稳定深度与断面处年平均温度呈现线性相关关系,而与温度变幅呈现非线性相关的关系。基于冻结锋面移动规律,对保温隔热层厚度计算公式中的冻深参数进行了修正,保证了保温层长期有效服役。     

深埋三车道大断面隧道二次衬砌厚度优化分析

为了研究合理的二次衬砌支护参数,以陕西省宝鸡到汉中高速公路铁佛殿1号隧道工程为例,通过运用MIDAS软件建立数值计算模型的方法,对Ⅳ级、Ⅴ级围岩条件下的深埋三车道隧道二次衬砌进行数值模拟分析,并对不同的二次衬砌厚度进行了安全系数计算。结果表明:深埋三车道大断面隧道Ⅳ级围岩二衬厚度优化至设计值75%、Ⅴ级围岩优化至设计值80%时,隧道结构安全系数满足规范要求。可见目前的公路隧道设计规范对于二次衬砌厚度的规定偏于保守,对于一般情况的隧道设计,有必要进一步减薄优化。     

麦秸刨花板的吸水厚度变化模型

通过理论推导和实验数据的拟合曲线求得麦秸刨花板的吸水厚度变化模型,模型的应用结果表明：麦秸刨花板中胶粘剂的MDI用量越多,其最大的吸水厚度膨胀率越低,尺寸稳定性越高,当麦秸刨花板的密度从0.65g/cm^3增加到0.75g/cm^3时,其尺寸稳定性略有改进,厚度为10mm的麦秸刨花板,当热压温度取150℃,热压时间从6min增加到10min的过程中,麦秸刨花板的吸水厚度膨胀率开始呈下降趋势,随后增加。     

Performance improvement for air-cooled open-cathode proton exchange membrane fuel cell with different design parameters of the gas diffusion layer

Air-cooled open-cathode LTPEMFC (AO-LTPEMFC) has been developed as a new power source for the portable power supply. The effect of the gas diffusion layer (GDL) on AO-LTPEMFC operation in challenging ambient air conditions was investigated in the present study. The effect of the content of polytetrafluoroethylene (PTFE) on the substrate layer and microporous layer (MPL), the thickness of GDL and the pulse width modulation (PWM) of the fan on cell performance as well as the cathode outlet surface temperature distribution were investigated. The polarization curves, electrochemical impedance spectroscopy (EIS) and dynamic voltage test were used to correlate the structural characteristics of GDL with heat dissipation, oxygen transport and water management in AO-LTPEMFC. The results showed that GDL with appropriate PTFE content in the substrate layer and MPL could significantly optimize cell performance. In addition, the thickness of GDL also had a certain impact on the mass and heat transfer of the fuel cell, while the water management in GDL was affected by PWM of the fan, simultaneously. Combined with the practice process, the optimum values of the substrate layer PTFE content, MPL layer PTFE content and thickness of GDL were identified to be 10%, 40%, and 200 μm, respectively.     

Film thickness effects on nanorods organic films of azo quinoline derivatives for optical applications

The effect of film thickness on the structural and optical properties of bisbenzimidazo [2,1-a:2′,1′-a′] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-10,21-dione (BI-diisoQ) films was carried out. The morphology of BI-diisoQ film showed a definite shape of a nanorod with a length of around 5 μm and a diameter of approximately 20 nm. Also, X-ray diffraction patterns demonstrated that BI-diisoQ thin films are characterized by a mixture of amorphous and crystalline structure, whereas the phase-nature crystallization of BI-diisoQ film enhanced as the film thickness increased. The investigation of the absorption coefficient of BI-diisoQ films revealed two indirect allowed band gaps energy. The calculated values of nonlinear optical parameters for BI-diisoQ film were observed to be increased with the increase of film thickness. The optical properties of BI-diisoQ nanorod films indicated that these films have appropriate optical properties, and thus it can be recommended as a promised candidate material in superconductors, optoelectronic and photonic applications.     

运算电容式传感器用于铝氧化膜厚度测试的研究

本文通过对运算电容式传感器及铝氧化膜厚度测试的实验研究,分析了影响测试精度的主要因素,并给出了校正方法和实用测量模型。     

煤田三维地震综合解释技术应用研究

本文以矿方建设高效、安全生产的现代化矿井要求为出发点,阐述了三维地震解释技术的发展,指出了地震多属性提取和波阻抗反演技术应用的实际意义,通过对陕北某矿三维地震勘探的应用实例,提出了地震多属性提取技术在预测煤厚、煤层冲刷范围等方面具有较好的应用效果;根据波阻抗反演技术在河南某矿的应用实例,提取了全区煤层顶板波阻抗值,并与钻孔揭露的岩性之间建立一定的对应关系,实现了对全区煤层顶板岩性的预测.     

含水率及夹层厚度对软弱夹层强度影响分析

软弱夹层对斜坡及围岩稳定性影响较大,对其剪切力学特性的研究具有实际工程意义。巴东组第三段(T₂b³)特殊岩体特性使风化后的软弱夹层和地下水中含有较多CaCO₃,使软弱夹层力学性质发生改变。基于此,以三峡库区巴东组第三段泥灰岩和层间软弱夹层为研究对象,对土-岩剪切试样进行室内直剪试验及微计算机断层扫描试验、电镜扫描试验,从宏微观角度重点研究含水率、夹层厚度及CaCO₃含量对软弱夹层抗剪强度的影响规律及动态特性。研究表明:CaCO₃通过降低土体孔隙率和改变土颗粒形态提升内摩擦角,通过增强土体胶结能力提升内聚力,从而增大其抗剪强度。低CaCO₃含量下,试样抗剪强度随含水率的增大而减小;高CaCO₃含量下,18%含水率以下时,抗剪强度随含水率的增大而增大,而到22%时抗剪强度突降。低法向应力下,试样抗剪强度受夹层厚度影响较小且随CaCO₃含量的增大而增大;高法向应力下,从高夹层厚度低CaCO₃含量到...