基于弹性层状体系理论下的重载铁路轨道 结构动力响应研究

通过分析重载铁路轨道结构的受力特征,得出车辆荷载在轨枕上的分担规律。基于二维弹性层状体系理论建立了重载铁路轨道结构的层状体系力学模型。利用MATLAB软件编制相应的程序计算出弹性层状体系的理论解,将得出的计算数据和大秦线实测数据做对比分析,检验出计算程序的正确性和弹性层状体系理论研究方法的可行性,为今后重载铁路轨道结构动力响应的研究提供了一套新的思路和方法。     

机械臂刚体运动防冲突角度最优输出方法

机械臂刚体运动防冲突角度输出方法存在防冲突角度控制精度低、易出现碰撞的弊端;因此,提出一种机械臂刚体运动防冲突角度最优输出方法。利用拉格朗日法获取机械臂被动关节动力学方程式,通过振幅控制方法控制机械臂被动关节位置,实现对机械臂刚体运动防冲突角度的最优输出。实验结果表明,相对于传统方法,控制下的机械臂刚体运动防冲突角度输出值较优,控制过程中位置误差与稳态误差较小,有效实现了机械臂运动的防碰控制。     

Dependence of mechanical behavior on grain size of metastable Ti–Nb–O titanium alloy

Cold-rolled metastable β-type Ti–38Nb-0.2O alloy was subjected to annealing treatment to obtain different precipitates and grain sizes. The influence of annealing on microstructure and mechanical properties was investigated. The alloy annealed at 673 ?K or 773 ?K exhibited a single-stage yielding with high strength and low uniform elongation, due to the residual work hardening and the precipitation of ω or α phases. The alloy annealed at above 873 ?K exhibited an obvious double yielding behavior resulting from the stress-induced martensitic transformation. The grain growth kinetics of single β phase alloy is sensitive to temperature, and it is suggested that the existence of oxygen decreases the grain growth exponent and increases the required activation energy for grain growth. The critical stress for slip decreased monotonously with the increase of grain size, following the classic Hall-Petch relationship. However, the critical stress for martensitic transformation decreased to a minimum and then increased again, as the grain size increased. The results are worth for design of the heat-treatment parameters of the Ti–38Nb-0.2O alloy for engineering applications.     

Improving the tensile properties of extruded Mg–Ga alloy by ageing treatment

A hot-extruded Mg-5Ga alloy was subjected to ageing treatment at 150 ?°C, 190 ?°C and 230 ?°C. The microstructures and mechanical properties of the extruded and aged alloy were examined in this study. Microstructure examinations suggested that particle-shaped and rod-shaped Mg₅Ga₂ were precipitated in the alloy after peak ageing treatment. The extruded alloy showed the yield strength, ultimate tensile strength and elongation to fracture of 157.6 ?MPa, 248.6 ?MPa and 17.5%, respectively. After peak ageing, the yield strength and ultimate tensile strength can be enhanced by as much as 15.7% and 8.6% reaching 182.3 ?MPa and 270 ?MPa, respectively. The improvement of the tensile strengths is mainly attributed to the enhanced precipitation strengthening by newly formed fine Mg₅Ga₂ precipitates. The ductility of the alloy was slightly increased by peak ageing at low temperatures (150 ?°C and 190 ?°C), but remarkably decreased by peak ageing at high temperature (230 ?°C) due to the formation of coarsened Mg₅Ga₂ particles which easily initiated the cracks during tensile deformation.     

Microstructure evolution of Ti–6Al–4V under cold rolling + low temperature nitriding process

A new nitriding process modifying both the surface and the matrix is proposed to improve the poor wear resistance and low hardness of the titanium alloy surface. The treatment of solid solution treatment, cold rolling and low temperature nitriding was used for surface modification. The results showed that the microstructure of the Ti–6Al–4V(TC4) titanium alloy sample changed from the original α+β phase to the residual α phase, metastable β phase and martensite α′ phase after solution treatment. The results of cold rolling experiments indicated that with the increase of rolling amount, many defects generated, and the grains were first elongated and then partially broken. During the process of low-temperature nitriding the recrystallization occurred, which effectively avoided the problem of coarse matrix structure. It has been found that after low-temperature nitriding, thin strip-like α-phase with dispersed distribution, which is a typical aging structure, formed. The XRD test results indicate that steady state nitrides Ti₂N formed on the surface of the sample, but the content of Ti₂N was relatively low. Based on the morphology of content of the surface and cross-section it is believed that a special type of nitriding layerformed after low-temperature nitriding. The mechanical performance test results indicate that the wear resistance and hardness of the alloy increased significantly.     

单差载波相位自主完好性监测算法

应用载波相位差分定位时,由于多路径误差、卫星信号遮挡、卫星故障等原因,易造成载波相位测量值发生偏差和周跳,因此必须进行完好性监测。研究了利用单差载波相位测量值进行载波相位完好性监测的方法,固定整周模糊度值之后,利用最小二乘残差构造检验统计量,根据虚警概率和观测到卫星个数设定门限值,对单差载波相位测量值进行监测。分析了垂直保护级和漏警概率、卫星个数的关系。实验结果表明,虚警概率取为10-7/历元时,算法能有效检测测量偏差,对小至0.4周的偏差,比原有算法检测能力较强;漏警概率取为10-6/历元,垂直告警限值取为1.1m时算法满足可用性要求,增加1颗观测卫星能使垂直保护级降低约2cm。     

格模型的安全性分析

分析了格模型以及格模型的各种实施机制,指出了该模型的二类实施机制在精确性上存在的问题.同时,提出了局部安全性和整体安全性二个不同概念,指出了该模型在整体安全性上的弱点,最后论证了格模型不具有保护信息完整性的能力.     

浅谈机电类专业《机械制图》课的教学改革

主要探讨了在新形势下如何针对机电类专业的《机械制图》课程修订教学目标,重组教学内容,改革教学方法,提高教学效率,走出一条创造性教学新路。     

正确处理新形势下人民内部矛盾与构建社会主义和谐社会

构建社会主义和谐社会,必须正确处理新形势下人民内部矛盾。阐述和分析了社会主义和谐社会的本质内涵及新形势下人民内部矛盾的形式和特点,揭示了正确处理新形势下人民内部矛盾与构建社会主义和谐社会的内在统一性,提出了正确处理新形势下人民内部矛盾的措施和办法。     

机械创新设计中创造性思维的研究

通过对创造性思维概念、基本特征、基本形式及其应用的研究，阐述了创造性思维在机械创新设计中的重要性，并且给出对老式电风扇进行创新设计的实例．