Control of microstructure shape and morphology in femtosecond laser ablation of imprint rollers

With increasing demand for microstructure shape accuracy for MEMS and optoelectronic devices, controllability of shape and morphology in micro-fabrication has become increasingly crucial. In this paper, the effects of processing parameters on the shape and morphology of microstructures in femtosecond laser fabrication of imprint roller are explored. An optimized fabrication process is proposed to acquire high accuracy microstructures, in which a two-step inclination ablation process and optimal laser focus position are adopted. Adjusting and matching the processing parameters is a basic method to acquire well-defined shapes, but the ablation results indicate that the draft angle of microstructures can only be adjusted in a limited range due to the intensity distribution of laser beam. A two-step inclination ablation process is adopted to increase the draft angle. In the two-step inclination ablation process, the laser beam irradiates the target surface with an angle and the microstructure with a much steeper draft angle forms after the two-step fabrication. Laser focus position is explored as an important parameter affecting the morphology, and an optimal laser focus position is obtained to enhance the ablation quality. By matching the laser fluence and laser focus position, this morphology enhancement method can realize the high-quality ablation of microstructures with a wide range of dimensions without changing the focusing objective lens.     

基于统一强度理论的断裂准则

基于统一强度理论,在小范围屈服条件下,推导Ⅰ、Ⅱ复合型裂纹裂尖塑性区范围的统一解析解。给出不同拉压比α、泊松比υ、中间主应力影响参数b以及裂纹倾角β下的一族塑性区形状与大小的轨迹,讨论以上参数对裂尖塑性区变化的影响。最后基于裂纹尖端塑性区的解析解,提出了一种复合型裂纹断裂准则,分析了裂纹倾角与初始断裂角的关系。结果表明,该准则预测结果比其它准则更精确,与试验结果吻合得非常好。     

基于FLUENT的静压轴承椭圆腔和扇形腔静止状态流场仿真

对重型立式数控车床工作台静压导轨进行研究,应用三维造型软件Pro/ENG INEER及CFD软件FLUENT,从结构三维造型设计以及内部三维流动分析计算两方面对静压轴承进行了综合分析,并对比了不同形状油腔的流速分布及压力分布,揭示了导轨内部流动规律。结果表明:由于油腔形状不同,导致与上工作台的有效接触面积大小不同,扇形油腔各个方向速度在迭代计算后更容易收敛且更容易趋于稳定,而椭圆形油腔各个方向速度波动性较大;利用CFD技术对液体静压轴承进行三维数值模拟,得到的流场结果与实际吻合,计算结果能够有效反映轴承内的流动状态。     

叶盘结构频率转向特征及失谐敏感性实验研究

搭建了用于失谐叶盘结构固有特性及失谐敏感性研究的实验平台,对谐调叶盘结构的频率转向现象进行了实验研究,验证了以往理论分析和有限元仿真中发现的频率转向特征和模态振型转换现象;通过在叶尖粘贴不同的质量块,模拟了三种典型的叶片失谐形式,实验研究了失谐叶盘结构的模态局部化问题;针对同一叶片失谐形式下不同的模态密度区域,实验研究了模态密度对失谐敏感性的影响规律。实验结果与有限元实验仿真结果吻合较好。     

空间光谱仪指向机构的力学分析

为了准确分析空间CO2光谱仪指向机构的力学特性,本文根据轴承结构参数,建立了轴承有限元接触分析模型。计算了不同载荷下轴心的位移量,用多项式对计算结果进行拟合得到轴承非线性刚度曲线。在指向机构有限元力学模型中,利用相应刚度的弹簧单元替代轴承结构,经过有限元频率响应分析后获得指向机构的动态特性。仿真实验显示:在重力工况下指向镜的面形在光轴和子午方向分别为19.23nm和19.27nm,满足优于λ/30(均方根值RMS,λ=632.8nm)的设计要求,3个方向基频均大于100Hz。振动试验显示,3个方向基频均优于100 Hz,振动试验后反射镜镜面面形精度为λ/35。分析结果与仿真结果相符,表明利用非线性接触分析方法可以较为准确地求解轴承刚度,同时空间光谱仪指向机构静/动力学性能满足设计要求。     

迷宫密封流场与泄漏特性研究

应用Fluent软件计算迷宫间隙、齿厚、空腔深度和不同齿型对迷宫密封流场和泄漏量的影响。计算结果表明:迷宫密封泄漏量随间隙宽度呈线性变化;随着密封齿厚度的增加,泄漏量相对减少,泄漏量按线性关系变化;对于空腔深度而言,空腔深度越大,紊流程度下降,泄漏量越大;对不同齿型,半圆形密封齿泄漏量最大,其次是弧形齿,在实际应用中应多使用直齿,梯形齿和三角齿,以减少泄漏量。本研究可为迷宫密封设计与应用提供依据。     

Effect of rotating,non-axisymmetric cavitator on supercavity size

This study was conducted using a rotating non-axisymmetric cavitator to artificially increase the size of the cavity. Computational analysis was performed to predict the size of the cavity with a cavitation number of 0.3. To analyze the effect of the shape of the cavitator, six cavitator shapes were used by combining the cavitator thickness, the angle of the blades, the angle between the side surface of the blade and the rotating direction. The results of the study showed that the length of the cavity increased as the rotation velocity increased during the rotation of the cavitator. The drag force increased as the rotation velocity increased, but the increase was small. As a result, the length of the cavity for the same drag increased significantly as the side surface of the cavitator was perpendicular to the direction of rotation and the thickness of the cavitator was thick. The length of the cavity against the same drag was larger than that of a conventional disk cavitator.

     

Improved mathematical model of the wear of the cup articular surface in hip joint prostheses and comparison with retrieved components

This paper presents an analytical model of the cobalt-based alloy-ultra-high molecular weight polyethylene (UHMWPE) wear coupling. Based on a previous model in which the cup wear volume over a gait cycle (WG) was calculated under the simplifying assumption of an ideal rigid coupling, the current version proposes a more realistic wear simulation. All three components of the hip loading force were considered for the contact pressure calculation and all three components of the hip motion were taken into account for the sliding distance calculation. The contact pressure distribution was calculated on the basis of the Hertzian theory for the elastic contact of two bodies with non-conforming geometrical shapes. The wear factor was taken from hip simulator wear tests. The calculated WG is 67 x 10(-6) mm3 for a standard reference patient. The parametric model simulations show that WG increases linearly with the patient weight, femoral head diameter and surface roughness. It increases non-linearly to a maximum and decreases to an asymptotic value with increasing cup/head clearance and with cup isotropic elastic modulus. The cup orientation in the pelvis affects only slightly the total amount of WG whereas it is the dominant factor affecting the shape of the wear distribution. The iso-wear maps show paracentral patterns at low cup inclination angles and marginal patterns at higher inclination angles. The maximum wear depth is supero-posterior when the cup is in neutral alignment and supero-anterior at increasing anteversion angles. Complex patterns with a combination of paracentral and marginal wear were obtained at specific clearance values and cup orientations. The results of the simulations are discussed in relation to the wear distribution measured on the articular surface of 12 UHMWPE components retrieved from failed hip joint prostheses, after a period of in situ functioning.     

轴承非线性特性对摆线针轮减速器传动效率的影响分析与参数确定

为构建考虑轴承接触弹性的摆线针轮传动效率理论计算方法，并揭示轴承非线性刚度的影响机制，提出一种耦合摆线轮设计参数、接触载荷及轴承参数的传动效率理论模型。该模型考虑了输入轴与摆线轮的轴承弹性，并引入非线性的轴承刚度。采用牛顿法建立摆线轮受轴承弹性力、惯性力及接触载荷时的动力学微分方程，求解该方程得到轴承弹性位移，并将其与轴承刚度参数纳入传动效率计算模型。通过对比分析不同轴承刚度参数和运行工况下的理论传动效率，并利用理论计算效率与实验测定值的差异，对理论模型加以修正并迭代计算，从而拟定轴承参数。分析表明：轴承刚度指数较小时传动效率受运行速度和负载影响很小，轴承刚度指数较大时传动效率随着负载增大而提高；拟定刚度模型具有合成效应且给定合理参数下所得传动效率与测试值大致相符，可为摆线针轮传动效率评估提供高效且准确的理论方法。     

Contact force studies of a burnishing slider

In order to design the flying height of a burnishing slider accurately, the contact force between the burnishing slider and the disk needs to be well evaluated. This paper studies the contact force of a burnishing slider by both experiment and simulation. The experiment is conducted by measuring the acoustic emission signals of the contact force avalanche, and the simulation is based on the self-developed air bearing surface simulation code applying the probability model for the contact force calculation. The influence of contact force on the burnishing effect is discussed. It is observed that the simulation results are well correlated with the experimental measurements. It is believed that the simulation code is capable to design burnishing sliders with reasonable accuracy.     

Design of a surface replacement prosthesis for the proximal interphalangeal joint

A surface replacement finger joint prosthesis was designed specifically for the proximal interphalangeal joint (PIPJ). The two-piece design consisted of a bi-condylar proximal phalangeal head and a conforming bi-concave middle phalangeal base. The bearing surfaces were designed as close to the original anatomy of the PIPJs as possible, using detailed information obtained from a previous anatomical study of 83 PIPJs by the present authors. Four sizes of prosthesis were designed with maximum head diameters of 7, 8, 9 and 10 mm. Fixation of the joint prosthesis was achieved by an interference fit between the stems of semicircular cross-section and the phalangeal bone shafts. The main considerations for the stem designs were the offset from the centre of rotation, angle of inclination, length, and cross-sectional shape and size. It is proposed that the two components will be made from cross-linked polyethylene (XLPE) because it can be injection moulded to produce the complex shapes of the joint prosthesis. In addition, XLPE against itself has shown comparable wear rates with stainless steel against ultra-high molecular weight polyethylene from previous work by Joyce et al.     

轿车轮毂轴承铆装工艺理论分析与试验研究

对轿车轮毂轴承单元的铆装工艺进行了理论分析和试验研究。建立了铆装力理论计算模型与铆装工艺有限元分析模型,研究了铆头轨迹、倾角和停留时间等工艺参数对铆装质量的影响,得出采用圆周轨迹、铆头倾角6°和停留时间0.8s时铆装质量最好的结论。以DAC2F10轿车轮毂轴承单元为例,在课题组开发的铆合装配专用机床上进行了铆装试验,验证了铆装力理论模型和铆装工艺有限元模型的合理性,并进一步优化铆头倾角为5.5°。采用所优化的铆装工艺试制出了轮毂轴承单元样件,耐久性试验测试最高使用寿命近2×105km,表明得出的铆装优化工艺能大幅提高轮毂轴承单元的使用寿命和可靠性。     

Film height optimization of dynamically loaded hydrodynamic slider bearings

A method is presented to determine the optimal surface shape distribution for a hydrodynamic slider bearing. This is the surface shape distribution that is able to carry a prescribed load while maintaining a maximum separation between the surfaces. This method is first derived for a bearing with constant load and sliding speed. It is subsequently extended for a bearing with periodic load and sliding speed. Results for slider bearings with different shapes, loads and speeds are presented. It is shown that the numerical procedure developed in this paper is numerically more efficient than a reference optimization method.     

Series expansions for the dimensionless load capacity per unit width of a plane infinite slider bearing

Two series expansions are given for W_∞, the dimensionless load capacity per unit width of an infinite plane slider bearing. One series, which is new, is valid for all inclinations of the bearing pad, whereas the other diverges for an inclination parameter greater than unity. Either series can be used to calculate accurate values of W_∞ at low bearing pad inclination. The new series provides an accurate method for calculating W_∞ for use in the calculation of the dimensionless load capacity per unit width of a plane finite slider bearing either in single precision on a computer or by means of a programmable desktop calculator     

Shape error compensation in flexible forming process using overbending surface method

In this article, the design of the flexible forming process considering die shape compensation using an iterative overbending method based on numerical simulation is carried out. In this method, the springback shape obtained from the final step of the first forming simulation is compared with the desired objective shape, and the shape error is calculated as a vector norm with three-dimensional coordinates. The error vector is inversely added to the objective surface to compensate both the upper and lower flexible die configuration. The flexible dies are made up of several punches that make a forming die that is equivalent to a solid die, thus the forming surface shape can be reconfigurable with regard to the compensated die shapes. The flexible die shapes are recalculated, and the punch arrays are adjusted according to the overbent forming surface. These iterative procedures are repeated until the shape error variation converges. In addition, experimental verification is carried out using a 2,000-kN flexible forming apparatus for thick plates. Finally, the configuration of the prototype obtained from the experiment is compared with the numerical simulation results, which have consideration of the springback compensation. Consequently, it is confirmed that the suggested method for compensating the forming error could be used in the design of the flexible forming process for thick-curved plates.     

推力球轴承接触问题有限元分析

推力球轴承是被广泛应用的支承机械,用于承受转速较低的轴向载荷.它是由上下座圈、保持架和球体组成的可分离结构,分为单向推力球轴承和双向推力球轴承两种.着重分析了不同尺寸、形状的球形滚动体和橄榄球形滚动体对接触情况下的应力和变形量的影响.使用Pro/E建立实体模型,导入ANSYS进行数值模拟和计算.通过对获得的数值模拟结果和赫兹理论解进行对比,结果表明有限元分析是比较准确而且可靠的.最大接触应力和弹性趋近量取决于滚动体与滚道接触处的主曲率和、主曲率差,与滚动体形状、体积没有直接联系.     

Numeric and experimental study of generalized geometrical design of a hydrodynamic journal bearing based on the general film thickness equation

This paper deals with multi-objective shape optimization related to the geometrical design of a hydrodynamic journal bearing. The aim proposed here is to show that optimum shape design with better performance could surpass the limitations of existing bearing profiles. Attempting to remove the difficulty of selecting the weighting factor in multi-objective journal bearing optimization problems, a modified non-dominant sort in genetic algorithm was used as an optimization tool with a penalty to those solutions that violate constraints. Three kinds of optimized shapes were manufactured and taken as experimental objects. Experimental apparatus was described and some experimental data was presented. The comparison was made for the optimized bearings between numeric values and experimental data. The results show that the new method for shape optimization of hydrodynamic journal bearings based on the general film thickness equation is feasible.     

超高速磨削机床主轴系统模态分析

针对液体动静压轴承支撑的超高速磨削主轴系统工作的特殊性,在机床工作过程中,主轴高速旋转,动静压轴承的支撑刚度随转速动态变化.为了解主轴系统工作过程中的动态特性,应用Flunent软件求解液体动静压轴承的动态支撑刚 度,而后在此基础上利用有限元分析软件ANSYS建立超高速磨床主轴系统的三维有限元模型,并对其进行模态分析,得到了各阶固有频率和振型.通过设置不同转速下轴承的支撑刚度,获得主轴系统模态分析结果,并利用图解法求解出主轴系统的临界转速.分析结果表明主轴系统在高速旋转状态下,系统的结构刚度会发生变化,使主轴系统的固有频率改变,并且随着转速提高差异越显著.通过振动试验测试验证仿真分析的可靠性,经分析可知,试验与仿真的误差主要来源于支撑模型的简化.     

圆盘锻件纯形状锻造模具优化设计

在讨论圆盘锻件模具设计现状的基础上,提出了一种金属成形过程的有限元灵敏度分析方法和以此为基础的模具形状优化设计方法。对圆盘件锻造过程进行了灵敏度分析和模具形状优化设计。结果表明,采用优化设计的预锻模具,可得到侧面无鼓形的纯形状圆盘锻件,并且预锻模具形状光滑、简单、便于加工和锻造生产。为圆盘锻件的纯形状锻造模具设计提供了一种定量分析方法。     

静压向心轴承的结构创新设计

为提高矩形油腔静压向心轴承工作时产生的动压效应，设计了一种含矩形油腔、“门形”油腔和“回形”油腔的复合式油腔结构的新型静压向心轴承，该结构轴承在产生足够的静压承载能力的基础上可产生很强的动压效应。经理论分析与实验表明，复合式油腔静压向心轴承的承载能力和油膜刚度较常规使用的矩形油腔静压向心轴承均有大幅度提高。轴承的偏心率可由截流器无级调节。