数控伺服系统跟踪及轮廓误差分析

分析了数控加工中伺服系统跟踪误差和轮廓误差的计算方法,详细讨论了双轴数控加工中轴跟踪误差和轮廓误差之间的关系。指出了多轴加工中轮廓误差建模和误差控制方法的理论意义和应用价值。     

MESHFREE METHOD BASED ON POINT COLLOCATION FOR METAL FORMING SIMULATION

A meshfree method based on reproducing kernel approximation and point collocation is presented for analysis of metal ring compression. The point collocation method is a true meshfree method without the employment of a background mesh. It is shown that, in a point collocation approach, the remesh problem because of the mesh distortion in FEM （finite element method） and the low efficiency in Galerkin-based meshfree method are avoided. The corrected kernel functions are introduced to the stabilization of free-surface boundary conditions. The solution of symmetric ring compression problem is compared with a conventional finite element solution, and reasonable results have been obtained.     

铰链梁铸造缺陷分析及对策

分析了HTDS-034DM压机铰链梁的生产工艺及主要铸造缺陷，提出了其铸造生产的改进措施。结果表明：采用底注开放式浇注系统，加大浇口面积以提高浇注速度，大砂芯内填充草绳以增加砂芯的退让性，开设好内砂芯的排气系统，做好铸型表面涂料的涂刷及烘干，熔炼质量合格的钢水以及合适的浇注温度是生产合格铰链梁铸件的关键。     

Fabrication of niobium doped Pb（Zr, Ti）O3 fibers by viscous polymer processing

A technique based on viscous polymer processing （VPP） was described, which can produce high ceramic content green fibers. PZT-5 ceramic powders were ball milled to get high dispersibility. The slurry prepared for VPP was a composition of PZT-5 powder, PVA binder and glycerin. High ceramic content PZT-5 fibers were extruded with the slurry. The results show that the ceramic powders have fine mean particle size of 0.54 pan, high specific surface area of 3.55 m^2/g and zeta potential of 8.81 mV after 16 h milling. The fibers sintered at 1 280 ℃ for 4 h have pure perovskite structure and grains of 2-5 μm in size, with little pores or cracks. The ultimate tensile strength of sintered fibers is up to 13.84 MPa compared with 2.88 MPa of green fibers. The remnant polarization （Pr） and coercive field （Ec） of the fibers are 50.65 μC/cm^2 and 2.45 kV/mm, respectively. This fiber can withstand an electric field of 9 kV/mm higher than the ceramic （5 kV/mm）, which shows high directional and compact qualities.     

Mechanical properties of nano SiO2 filled gypsum particleboard

Nano SiO2 was filled into gypsum particleboard. Effect of the amount of nano SiO2 particles filled, ultrasonic dissipating duration and treating the nano particles with different coupling agents on the mechanical properties of the board were studied respectively. The results show that nano SiO2 is helpful for the improvement of the properties. Adding 3%（mass fraction） nano SiO2 is the best for the improvement of both modulus of rupture（MOR） and modulus of elasticity（MOE） of the boards formed at 30 ℃ or 40 ℃. For the boards formed at 30 ℃, their MOR and MOE can be improved by 8.77% and 12.24%, and MOR and MOE of the boards formed at 40 ℃ can be improved by 44.44% and 108.38%.3% is also the best addition proportion to improve internal bond（IB） of the boards formed at 30 ℃, while 5% is the best for that of the boards formed at 40 ℃. At room temperature, dissipating nano Si02 into flake by ultrasonic has better effect on the properties of the final products. Through ultrasonic treating for 1 h and the best treating duration, the MOR and MOE can be increased by 41.99% and 47.80%. In addition, different coupling agents have different effects on the final properties too, and silane coupling agent KH570 is better for the improvement of properties of the boards formed at room temperature.     

Microdefects and electron densities in NiTi shape memory alloys studied by positron annihilation

1Introduction NiTi alloys are the most successful shape memory alloys as a result of their combination of good functional properties and excellent mechanical strength[1,2].The thermal and mechanical shape memory behavior in these alloys is dependent upon …     

MoS2-Ti复合膜的结构及其抗氧化性能

利用非平衡磁控溅射仪在碳/碳复合材料表面制备了MoS2-Ti复合膜.采用XRD,Raman光谱、X射线光电子能谱仪对其结构进行了表征,并利用X射线光电子能谱仪对复合膜的抗氧化性能进行了研究.研究结果表明:所制备的MoS2-Ti复合膜为非晶态结构;MoS2-Ti复合膜具有良好的抗氧化性能,将其在蒸馏水中浸泡200 h后,Mo4+没有被氧化.     

钎杆短期断裂失效分析

对短期服役后出现断裂失效的钎杆的断口形貌、金相组织进行了观察和分析，认为钎杆前端出现短期断裂失效的原因是前端存在较重的表面脱碳，而且该脱碳主要是在锻造前的加热过程中形成的。钎杆在服役过程中受到外力作用下短期内会很容易在较重的脱碳表面产生裂纹，然后裂纹逐渐扩展造成断裂。     

Ti-2Al-2．5Zr合金丝材延伸率影响因素分析

研究了组织形态、主要间隙元素O含量及热处理制度对Ti-2Al-2．5Zr钛合金丝材力学性能的影响规律。结果表明，O是丝材延伸率的主要影响因素，应对O含量做严格控制：均匀细小的等轴组织对丝材延伸率及强度的提高有利；在700℃-850℃进行真空退火，可使丝材具有较好的塑性与强度的匹配。通过以上研究，使丝材延伸率有较大提高，塑性、强度均稳定达到了相关标准要求。     

Mechanical Properties of Cr2AlC Ceramics

Dense and predominantly single-phase samples of Cr₂AlC, together with a trace amount of Cr₇C₃, were fabricated by hot pressing of a mixture of chromium, aluminum, and graphite powders at 1400°C for 1 h. The hardness, Young's modulus, flexural strength, and compressive strength of Cr₂AlC samples were 5.2, 288 GPa, 483±29, and 1159±23 MPa, respectively, which are comparable with those of Ti₃AlC₂ and Nb₂AlC. The material exhibits good damage tolerance. For indentation loads up to 50 N, the post-indentation flexural strengths decrease by approximately 10% and by 31% for a load of 100 N. The flexural strengths of Cr₂AlC samples quenched from 300°C to room temperature decrease from 483 to 455 MPa, while the retained strengths decrease quickly to 199 MPa when the quench temperature increases to 500°C. A further increase in quench temperature to 700°, 900°, and 1100°C results in a small reduction of strength.