醋酸钾对轻石脑油裂解结焦的影响

为考察碱金属元素对裂解结焦的影响,以醋酸钾为结焦抑制剂,在850℃下对退役25Cr35Ni炉管试样内表面进行了结焦实验。利用扫描电子显微镜(SEM)、场发射扫描电镜(FE-SEM)、能量色散谱仪(EDS）、X射线衍射(XRD)和Raman光谱对退役25Cr35Ni炉管试样内表面和焦层进行了表征。结果表明,退役25Cr35Ni炉管内表面主要由Cr_1.3Fe_0.7O₃相似文献   

复合化学镀层在盐化物料中的耐蚀性

采用极化曲线研究了不同磷含量的Ni-P镀层在盐化物料中的耐腐蚀性,对比了不同种类的复合化学镀层在盐化物料中的耐蚀性能,对镀层的组成、表面形貌以及镀层力学性能、孔隙率等进行了分析。结果表明,镀层在盐化物料中的耐腐蚀性与其成分关系密切。镍磷镀层的磷含量越高,耐腐蚀性越好;合金镀层中,Ni—Sn-P的耐蚀性能较Ni—Cu-P...     

玻璃与金属真空钎焊接头残余应力影响参数分析

玻璃和金属焊接接头由于设计不合理,将致使接头存在较大的焊接残余应力,会严重削弱接头强度.应用顺次耦合有限元热应力计算方法,对平板玻璃和金属在真空条件下的钎焊过程进行了数值模拟,分析了玻璃、金属、钎料厚度、钎焊压力和钎焊温度等因素对应力集中区域残余应力的影响,并观察了焊接接头拉伸断裂后的形貌特征.结果表明,金属厚度增加会增大残余应力,并且其对残余应力影响最显著;钎焊压力和钎焊温度的增加可以降低残余应力;玻璃和钎料厚度对残余应力的影响不大;焊接接头的拉伸断裂区域位于玻璃和金属焊接接头界面贴近玻璃一侧.     

The plastic flow and finite element simulation of plastic fine blanking

An idea of fine blanking is put forward where negative clearance affects plastic shearing and the plastic state of material in the shearing zone is examined under the condition of negative clearance. By analyzing of blanking force and stress, the paper brings forward a method of setting up the three-directions pressed stress. The method determines if the material of deformation field enters the plasticity regime. Some parameters that control when the material of blanked zone enters into the plastic state are given. The analysis indicates that the material stays in the plastic regime, when the specific energy of elastic deformation for common carbon steel Q235 reaches 8.34 MPa. The status of plastic flowing in the shearing zone is simulated.     

基于切片理论的水下灵巧手手指动力学分析

水中环境的影响使多自由度水下机械臂的动力学模型较为复杂．鉴于动力学模型对系统仿真、控制系统设计的重要性，本文基于切片理论对水下灵巧手手指的动力学进行分析；考虑水阻力、附加质量力的影响，建立了较为精确的动力学模型．采用SimMechanics进行了动力学仿真．仿真结果显示，水动力使手指运动轨迹偏离，因此，手指动态运动控制时必须对其进行补偿．     

Degradation Characteristics of Elastomeric Gasket Materials in a Simulated PEM Fuel Cell Environment

Polymer electrolyte membrane (PEM) fuel cell stack requires gaskets and seals in each cell to keep the reactant gases (hydrogen and oxygen) within their respective regions. The stability of the gaskets/seals is critical to the operating life as well as the electrochemical performance of the fuel cell. The time-dependant chemical and mechanical degradation of two commercially available silicones-based elastomeric gasket materials in a simulated fuel cell environment was investigated in this work. Two temperatures based on actual fuel cell operation were selected and used in this study. Using optical microscopy, the topographical damage on the sample surface due to the acidic environment was revealed. Atomic adsorption spectrometer analysis shows that silicon, calcium, and magnesium were leached from the materials into the soaking solution. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to study the surface chemistry of the elastomeric gasket materials before and after exposure to the simulated fuel cell environment over time. The ATR-FTIR and XPS test results indicate that the surface chemistry changed significantly and the chemical degradation mechanism is de-crosslinking and chain scission in the backbone. The microindentation test results show that the mechanical properties of the silicone materials changed significantly after exposure to the simulated PEM fuel cell environment over time.     

12CrlMoV过热器管劣化行为研究

通过高温时效试验、微观组织分析、碳化物萃取、碳化物相X—Ray衍射分析以及力学性能试验，研究了不同球化级别12CrlMoV过热器管钢的组织、碳化物含量、相组成以及力学性能。结果表明，碳化物含量与球化级别呈抛物线关系。球化是一个加速的过程，前期主要完成碳化物相种类转变，中后期主要表现为碳化物形态的变化。球化级别与碳化物相含量的比值（M23C6／M3C）近似呈抛物线关系。随着球化程度提高，材料高温强度下降，伸长率提高。     

自由落体冲击下模板支撑系统的动力分析

国内外在对模板支撑系统的设计普遍采用静力学的方法,这是直接导致模板支撑系统坍塌事故的重要因素之一。为了更好地反映结构的真实工况,采用动力学替代静力学的观点来设计与分析。通过有限元的瞬态动力学方法,建立模板支撑系统的动力学模型,对自由落体冲击下的高大模板支撑系统的动态特性进行了模拟,得到了结构静动态位移和应力。与理论方法相比较,验证了自由落体冲击动力系数与下落高度的关系。     

焊接残余应力在热处理过程中的演变

利用有限元法,对Q345R钢焊后热处理进行模拟分析.结果表明,焊态残余应力在焊缝和热影响区具有较高的应力水平,远离焊缝热影响区,应力逐渐降低.热处理后,残余应力降低了近60%,最大值位于热影响区浅表区域.热处理不仅使应力降低,同时使得应力发生再分布,母材热处理后应力增加.热处理过程中,随着温度升高,屈服强度降低,材料发...     

基于遗传算法和BP神经网络的花盘结构优化设计

综合利用有限元法、正交试验法、BP神经网络以及遗传算法对大重型数控转台的花盘结构系统进行优化研究。首先对花盘结构系统进行谐响应动力学分析,找出对结构动态特性影响最大的模态频率,并确定BP神经网络的输入变量,然后利用正交试验法和有限元分析法确定出BP神经网络样本点数据,建立反映花盘结构特性的BP神经网络模型,最后利用遗传算法对建立的BP神经网络优化。仿真结果表明,花盘第一阶固有频率提高15.5%,其自重降低9.8%。