椭球自由下落纯挤压弹流润滑研究

通过数值求解分析了椭球自由下落的纯挤压弹流润滑问题,通过合理定义速度、加速度和质量的量纲一参数,使得动力学方程的量纲一形式与有量纲形式得到了统一。使用多重网格技术在直角坐标系下的1/4域上求解,大大缩短了计算时间。数值计算结果表明:在整个撞击和反弹过程中,先有中心压力再有边峰压力,在椭球即将离开油膜时二者重合;油膜的纯挤压效应使得弹性表面出现了凹陷,压力主要分布在该凹陷区域内,而且凹陷里的油膜承受了主要的外部载荷。另外,椭圆比越大,整个撞击过程持续的时间越短,膜厚的变化越平缓,曲线的拐点越提前。最后,对文献[11]的试验曲线进行了数值模拟,理论曲线与试验曲线的吻合验证了程序的正确性。

等温粗糙表面的纯挤压弹流问题分析

假设玻璃盘表面分布有余弦波状的粗糙度,采用多重网格法和多重网格积分法对自由落体钢球冲击玻璃盘表面的等温纯挤压弹流问题进行数值分析,分析余弦波波长和钢球质量对润滑油摩擦性能的影响。研究发现,表面余弦波会造成压力和膜厚的剧烈波动,使中心压力升高,中心膜厚和最小膜厚降低;钢球质量越大,冲击-反弹时间越长,最小膜厚越小,而表面余弦波的存在又可进一步降低最小膜厚。

润滑油黏度和接触椭圆比对纯挤压热弹流润滑的影响

采用数值方法研究润滑油环境黏度和接触椭圆比对纯挤压热弹流油膜特性的影响。结果显示:随着黏度的降低,冲击-反弹总时间延长,中心压力峰值降低,第二压力峰变矮;与此对应的中心膜厚降低,中心温升也降低。随椭圆比的增加,冲击-反弹时间缩短,中心压力曲线的主峰和第二压力峰逐渐融合,压力幅值降低;中心膜厚则先增加后降低,最小膜厚则逐渐增加。与中心压力曲线的分布类似,中心温度的第二峰和主峰也逐渐融合,总体温升降低。

纯挤压弹流油膜对球面滚子简谐振动的响应

应用多重网格技术求解椭圆接触简谐振动球面滚子与无限大平面之间的弹性流体动力润滑问题,得到一组典型的数值解,并在该解的基础上分析不同的平衡位置、振幅和频率对中心压力和中心膜厚的影响。结果表明:在整个挤压反弹过程中,中心压力和中心膜厚随时间的变化曲线与稳态弹流润滑的压力和膜厚在空间上的变化曲线具有类似的特征,尤其是反弹阶段会出现较高的第二压力峰。经分析可知,该压力峰是由于反弹的最后阶段接触区中心处的凹坑消失,从而产生强烈的局部挤压效应所致。另外,结果显示,平衡位置的增大会缩短纯挤压的时间并减小中心压力的主峰高度,但会增加第二压力峰的高度,而振幅和频率的增加都会使纯挤压效应变得更强。

急停问题的椭圆接触弹流润滑分析

将机械急停时滚动轴承、齿轮等的弹流润滑油膜的渐变过程简化为从稳恒状态突然转化为恒载荷纯挤压状态,然后随时间的推移挤压效应逐渐消失的过程,建立了椭圆接触瞬态弹流润滑模型。假设润滑油为牛顿流体,在等温条件下用多重网格技术进行了动态数值求解,讨论了急停前卷吸速度分别沿椭圆接触区的长轴和短轴方向时,不同参数条件下的残留弹流润滑膜的压力和膜厚随时间的变化规律。数值计算结果表明,急停后润滑油会逐渐被挤出接触区,因此残留油膜只能保持很短的时间;较高的Hertz接触压力会通过增加润滑油粘度而延长残余油膜的维持时间,但不能根本上改变上述变化趋势,卷吸速度的方向也不能改变上述变化趋势。

Strain rate-dependent high temperature compressive deformation characteristics of ultrafine-grained pure aluminum produced by ECAP

To explore the effect of strain rate ε on the high temperature deformation characteristics of ultrafine-grained materials, the deformation and damage features as well as microstructures of ECAP-treated pure Al at different temperatures T and strain ratesε were systematically studied through compression tests and microscopic observations. The increase in ε eliminates strain softening at T≤473 K, and largely enhances the yield strength and flow stress at 473?573 K. The shear deformation dominates the plastic deformation of ECAP-treated Al. Many cracks along shear bands (SBs) are formed at T≥473 K and secondary SBs basically disappear at 1×10?3 s?1; however, at 1×10?2 s?1, cracks are only observed at temperature below 473 K, and secondary SBs become clearer at T≥473 K. The microstructures of ECAP-treated Al mainly consist of sub-grains (SGs). The increase in ε inhibits the SG growth, thus leading to the increases both in yield strength and flow stress at high temperatures.

Effect of processing route on grain refinement in pure copper processed by equal channel angular extrusion

An experimental study of the microstructures in pure copper billets processed by 8 passes of equal channel angular extrusion （ECAE） via an extended range of processing routes with a 90° die is carried out. Each processing route is defined according to the inter-pass billet rotation angle （χ）, which varies from 0° to 180°. According to the generation of high-angle boundaries and reduction of grain size by electron backscatter diffraction （EBSD） measurements, the grain refinement is found to be most efficient for route with χ=90°and least efficient with χ=180°, among the seven routes studied. This trend is supported by supplementary transmission electron microscopy （TEM） measurements. Comparison of the EBSD and TEM data reveals the importance of considering the non-equiaxity of grain structures in quantitative assessment of microstructural differences in ECAE-processed materials.

高尔夫球头用细晶纯Ti材料的组织及性能研究

高尔夫球头的高强度打击面非常关键,优异性能的球头材料能够保证良好的操控性和容错值、更高的击球精准度和更远的击球距离。采用高能球磨+冷等静压+真空烧结+热挤压工艺制备了细晶纯Ti材料,采用扫描电镜(SEM)和拉伸试验机对未挤压态和挤压态纯Ti材料的组织及性能进行了研究。结果表明:高能球磨5 h后,球形Ti粉末转化为细小的纳米碎颗粒,平均粒径由25μm降低至5μm以下,且分散均匀。挤压态细晶纯Ti的组织晶粒得到了充分细化,并且晶粒内部的微空隙缺陷消失。此外,挤压态细晶纯Ti的抗拉强度、屈服强度、伸长率相比于未挤压态均提高约16.1%、19.7%和16.3%。断口形貌显示挤压态细晶纯Ti的断口韧窝数量更多,而且深度小而均匀,撕裂棱分布的更加密集。

Microstructural approach to equal channel angular processing of commercially pure titanium——A review

A review on severe plastic deformation（SPD） technique of equal channel angular pressing（ECAP） process of commercially pure titanium（CP-Ti） alloys was presented with a major emphasize on the influence of ECAP parameters that include channel and curvature angles, processing route, temperature of operation, pressing speed, internal heating, number of pass through the die and back pressure. Various ECAP characteristics such as microstructure, strain inhomogeneity and mechanical properties are considered to achieve the maximum homogeneity, equilibrium grain refinement and mechanical improvement of CP-Ti. Investigations show that a pressing speed of 1-3 mm/s at 450 °C with route BC along with channel and curvature angles of 90° and 20° respectively with backpressure can lead to the most homogeneous ultrafine microstructure.

Mechanical responses, texture and microstructural evolution of high purity aluminum deformed by equal channel angular pressing

Ultrafine-grained(UFG) high purity aluminum exhibits a variety of attractive mechanical properties and special deformation behavior. Equal channel angular pressing(ECAP) process can be used to easily and effectively refine metals. The microstructure and microtexture evolutions and grain boundary characteristics of the high purity aluminum(99.998%) processed by ECAP at room temperature are investigated by means of TEM and EBSD. The results indicate that the shear deformation resistance increases with repeated EACP passes, and equiaxed grains with an average size of 0.9 μm in diameter are formed after five passes. Although the orientations distribution of grains tends to evolve toward random orientations, and microtextures(80°, 35°, 0°),(40°, 75°, 45°) and(0°, 85°, 45°) peak in the sample after five passes. The grain boundaries in UFG aluminum are high-angle geometrically necessary boundaries. It is suggested that the continuous dynamic recrystallization is responsible for the formation of ultrafine grains in high purity aluminum. Microstructure evolution in the high purity aluminum during ECAP is proposed.

Static mechanical properties and ductility of biomedical ultrafine-grained commercially pure titanium produced by ECAP process

Equal channel angular pressing(ECAP)is one of the most effective processes to produce ultra-fine grain(UFG)and nanocrystalline(NC)materials.Because the commercially pure titanium exhibits excellent biocompatibility properties,it has a significant potential to be utilized as an implant material.The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material.This defect can be removed by applying the ECAP process on the pure titanium.In this work,the commercially pure titanium Grade2(CP-Ti of Grade2)was pressed at room temperature by the ECAP process via a channel angle of135°for3passes.The microstructural analysis and mechanical tests such as tensile test,hardness test,three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through3passes.The microstructural evolution reveals that by applying the ECAP process,coarse grain(CG)structure develops to UFG/NC structure.Moreover,the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths,bending strength,hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.

专利信息 化工装备

一种纯剪切挤压制备超细晶粒管材的方法及设备 公开号:CN1473670A 公开日:2004.2.11 申请人:大连理工大学 一种纯剪切挤压制备超细晶粒管材的方法及设备,属于超细晶粒管材制备技术领域。它通过改变挤压成形的加工方式,实现了管材的纯剪切挤压变形。