Reliability analysis of ceramic cutting tools in continuous and interrupted hard turning

Reliability analysis was carried out for ceramic cutting tools used in continuous and interrupted hard turning. On the basis of micromechanics and damage mechanics, statistical characteristics of the original defects in the tool material microstructure were evaluated and analyzed. A new tool performance indicator was proposed considering the combined effects of the original damage of the tool material microstructure, the macro-mechanical properties of the tool material and the external loads on the cutting tool. Statistical analysis of the tool performance indicator was performed for continuous and interrupted turning. The relationship between tool reliability and the probability distribution of tool performance indicator was identified. It was found that the original damage of the ceramic tool material followed a weibull distribution. The probability density of the original damage decreased as the original damage increased. When interrupted turning was adopted, tool performance indicator was relatively low and the indicator decreased as cutting length ratio became smaller. The indicator followed a weibull distribution and this was invariable when turning condition changed. Relatively low shape parameter and scale parameter in probability density function of tool performance indicator appeared when the tool was tested in interrupted turning and relatively small cutting length ratio was applied. Similar to tool performance indicator, tool lives obtained under different cutting conditions also followed a weibull distribution. When turning condition varied, shape parameter and scale parameter in probability density function of tool life changed in a similar way to those parameters in probability density function of tool performance indicator. Both the probability density function of tool life and that of tool performance indicator first increased and then decreased as the independent variable increased. Shape parameter for tool performance indicator can be used in the calculation of tool reliability when the cutting length ratio in interrupted turning was relatively small.     

二维超声磨削纳米复相陶瓷表面残余应力研究

采用二维超声振动磨削和普通磨削方式,利用X射线衍射仪,对纳米复相陶瓷和氧化锆陶瓷表面残余应力的性质及大小进行了研究。实验表明,残余应力是磨削条件、相变应力和裂纹释放应力综合作用的结果。得到结论:在相同的磨削条件下,超声磨削的切向残余拉应力比普通磨削方式的小,法向残余压应力则比普通磨削的大;磨粒尺寸越小,残余拉应力越小;材料以塑性方式去除时,残余应力表现为压应力;超声磨削的m相变率比普通磨削的小。     

Flame dynamics analysis of highly hydrogen-enrichment premixed turbulent combustion

The highly hydrogen blended turbulent natural gas flames were stabilized on a nozzle-type Bunsen burner and measured with laser diagnostic technique. Flame topology characteristics and turbulent burning velocities for the lean turbulent combustion and uniform laminar flame speed of S_L ≈ 40 cm/s were investigated and compared. Hydrogen effect of high diffusivity on combustion properties was analyzed. The local flame structure parameters were obtained and analyzed. Results show that finer wrinkled structure is not only induced by increasing turbulence intensity u’/S_L, but also there is a significant enhancement due to the increasing hydrogen ratio. At large turbulence intensities for lean combustion, more elongated flame folds are formed and small scale structures are generated inducing flame pockets detaching from the main flame, which may largely due to the strong thermo-diffusive effect. However, when fixing S_L ≈ 40 cm/s, the flame front shows cusp structure with large negative curvature at high hydrogen ratio when u’/S_L is low, which mainly result from Darrieus-Landau instability in influencing the flame-turbulence interaction. Moreover, hydrogen addition apparently enhances turbulent burning velocity and the enhancement is more evident for higher intensities. S_T/S_L seems to follow the power law relation for lean flames while showing a quadratic relation for flame of S_L ≈ 40 cm/s. The PDF profile widens encompassing a larger range with increasing hydrogen ratio, indicating that the scale of wrinkled structure is getting smaller. This can be further verified by the profile of local radius of curvature. Hydrogen has an evident effect in enhancing flame surface density which may connect to turbulent burning velocity. And a slightly decreasing trend is found when ZH2 is beyond 0.6 at high u′/S_L.     

基于GIS的汽车燃油油量监测系统设计

采用GIS、GPRS、嵌入式、数据库等技术,设计了基于GIS的汽车燃油油量监测系统。该系统以嵌入式单片机为基础,可以对车辆的位置、油箱油量、瞬时油耗等进行实时监测、显示和上传到监控中心。此外系统采用模块化设计方法,实现了各个车载设备与监控中心的松散耦合,既具有高度集成性又可灵活搭配。该系统设计简单,可靠性好,易于安装,经济实用。     

具有初应力的多层空心圆柱体中的导波

基于“增量变形力学”理论,研究了轴向初应力和径向初应力对多层空心圆柱体中导波传播特性的影响,应用Legendre多项式方法求解了耦合波动方程,并通过数值算例讨论了该方法的收敛性,分析了初应力对纵向波和扭转波的影响,数值分析结果表明初应力对两者的影响是非常不同的。此外,轴向初应力对频散曲线的影响与径向初应力的影响也非常不同。     

金属表面疏水性研究进展

表面疏水性是近年来科学研究的热点。在生活中观察到荷叶表面上的水滴呈现圆球状,并能在荷叶上滚动而带走灰尘。研究发现荷叶表面具有优越的疏水性和自清洁特性,主要是由其表面微观的粗糙结构和低表面能物质共同引起的。概述了荷叶表面疏水性产生的原因,指出由于荷叶表面存在大量的微米级乳突,在这些微米级乳突上还有一些纳米级结构,这种纳米级结构正是引起荷叶表面超疏水的根本原因。归纳了疏水性表面的重要理论,其中,Young方程针对平整、光滑表面,将液滴在光滑表面上的张力和接触角联系起来;Wenzel模型是在Young方程的基础上引入了粗糙度因子,Wenzel模型中液滴形成的是一种非复合式的润湿状态,液滴和固体表面完全接触;Cassie方程是Wenzel模型的延伸,液滴和固体之间不再是单纯的非复合式接触,而是混有一定空气的复合式接触。在此基础上,综述了近年来表面疏水性的制备方法,包括化学法、特种加工法和微切削法等,最后展望了疏水性表面目前存在的问题。     

难加工材料铣削残余应力研究进展

镍基高温合金、钛合金等材料具有良好的高温强度、耐热性和耐腐蚀性等优异性能,已广泛应用于航空航天领域,然而这些材料属于典型的难加工材料,其相对切削加工性能很差,且已加工表面易产生显著残余拉应力,严重影响零部件使用寿命及性能。通过适当的方法调整和控制已加工表面的残余压应力,可以明显提高零件疲劳强度和耐腐蚀性。压应力制造技术是指以获得残余压应力为目标的制造技术,是一种典型的抗疲劳方法。将超声技术与其他加工方法复合实现残余压应力的主动控制,是目前抗疲劳制造技术的主要方法之一。然而,由于受超声加工的临界速度限制,超声与高速复合加工的研究相对较少,但两者均是目前压应力制造领域高度关切的先进加工方法,如果两者能有效复合,必将使核心部件制造在保证更加优良的抗疲劳性能的同时,获取更高的效率。通过分析铣削加工、高速加工以及超声振动加工中残余应力的研究现状,提出可将高速加工和超声振动加工相结合,从而实现难加工材料的高效压应力制造。     

小尺度受限空间内瓦斯湍流爆燃大涡模拟

构建了150 mm × 150 mm × 500 mm小尺度受限空间三维模型,基于火焰表面密度模型和Charlette湍流燃烧模型,对两侧连续障碍物条件下瓦斯爆燃火焰与湍流耦合过程进行了大涡模拟(LES)。模拟结果均与实验结果进行了比较。结果表明:大涡模拟可以很好预测瓦斯爆燃过程中的火焰结构、火焰锋面位置、火焰传播速度及超压,验证了大涡模拟及湍流燃烧模型对于瓦斯爆燃的适用性。此外,通过Karlovitz数定量描述了瓦斯爆燃火焰与湍流之间的相互作用及其变化规律,并对不同时刻的火焰模态进行了判别,在两侧连续障碍物条件下瓦斯湍流爆燃火焰先后经历波纹小火焰和薄反应区两种模态。     

Wave propagation in multilayered piezoelectric spherical plates

This paper proposes an improvement of the Legendre polynomial series method to solve the harmonic wave propagation in multilayered piezoelectric spherical plates, which are used in point-focusing transducers. The conventional Legendre polynomial method can deal with the multilayered structures only when the material properties of two adjacent layers do not change significantly and cannot obtain correctly normal stress and normal electric displacement shapes unlike the proposed improved orthogonal polynomial approach which overcomes these drawbacks. Detailed formulations are given to highlight its differences from the conventional Legendre polynomial approach. Through the comparisons of numerical results given by an exact solution (obtained from the reverberation-ray matrix method), and by the conventional polynomial approach and the improved polynomial approach, the validity of the proposed approach is illustrated. The influences of the radius-to-thickness ratio on dispersion curves, stress and electric displacement distributions are discussed. It is found that three factors determine the distribution of mechanical energy and electric energy at higher frequencies: radius-to-thickness ratio, wave speed, and position of the component material.     

切削法制备超细晶材料研究进展与展望

综述了切削法制备超细晶材料时加工参数和工艺条件对晶粒细化的影响,分析了切削法制备超细晶材料的力学性能、耐腐蚀性能和热稳定性等,探讨了超声振动复合切削法制备超细晶材料的可能性。在超声振动加工中,材料受低应力高速、高频撞击的影响,会发生严重的塑性变形,表面大尺寸的晶粒得到细化,同时超声振动还可以在材料表面形成表面微结构,进一步改善材料性能。因而提出将切削法和超声振动相复合,高效制备具有功能微结构的超细晶材料,为微型零件超细晶材料制备提供新的工艺选择以及理论和技术支撑。