车桥系统非平稳随机振动的PEM-PIM算法

研究了车桥耦合系统受到路面不平激励而发生的非平稳随机振动.采用虚拟激励方法(PEM)将路面的竖向随机不平度精确地转化为一系列竖向简谐不平度的叠加,从而简化了运动方程的求解,在此基础上用精细积分法(PIM)的三种格式进行数值计算.这种基于虚拟激励法的精细积分(PEM-PIM)算法比通常的数值积分方法更真实地模拟了车辆作用力在时间域和空间域上的连续变化,也更精确地实施了数值积分.与广泛采用的Newmark方法比较,三种PEM-PIM格式处理这类问题时在分析精度和计算效率上都有显著的改善,而又各有特色.     

Influence of soil deformation on off-road heavy vehicle suspension vibration

Analyses of the dynamic behaviour of a heavy vehicle during off-road operation are conducted under steady state condition. Three different numerical quarter-vehicle models (single point contact model, rigid wheel contact model and deformable wheel contact model) are introduced, and the simulation results are compared in order to find the most appropriate vehicle model. During the longitudinal travel of the vehicle, arbitrary ground profile is an input of vertical excitation to the vehicle. When ground deformation is included in the numerical model, the deformation filters the vertical excitation to the vehicle while the level of excitation varies depending on the soil deformability. Bekker's non-linear pressure/sinkage relationship is applied in modelling the ground behaviour. The simulations are conducted in the time domain and various surface roughness and ground deformability are applied in the ground/vehicle interaction during a parameter study. The ground deformation under the wheel acts like a non-linear spring during the vehicle movement and influences the vehicle vibration. If a vehicle mainly operates on off-road condition with high ground deformability lower value of damping is required in order to minimise the vertical body acceleration.     

桥梁表面不平顺对车-桥耦合振动系统动力效应的影响

利用模态分析法以及时变力学系统的求解方法,考虑桥面不平顺产生的随机激励,以简支梁桥为对象,计算了四自由度模型车辆-桥梁耦合系统的动力效应,讨论了不同等级桥面平整度情况下桥梁冲击系数、车辆垂直加速度、车轮对桥的作用力的变化规律。结果表明,随着不平整度系数逐渐增大,冲击系数逐渐增大;平整度较差等级的桥面,车辆垂直加速度较大,车轮对桥的作用力也较大。     

金刚石切削Soda-lime玻璃中的刀具磨损及其对工件表面粗糙度的影响

金刚石切削加工光学玻璃时,工件表面粗糙度与刀具磨损直接相关,为研究切削距离递增下的金刚石刀具磨损及其对工件加工表面粗糙度的影响,进行了Soda-lime玻璃金刚石切削的刀具磨损试验,并对刀具磨损形貌、后刀面磨损带的材料成份、工件的表面形貌及粗糙度进行了检测.结果表明:切削距离递增下的金刚石刀具前刀面磨损表现为平滑且均匀的月牙洼磨损,后刀面磨损表现为磨损带逐渐增大,且磨损带内有沿切削方向的微沟槽产生;切削距离未达到150 m时,工件表面粗糙度Rq、Ra及Rmax值始终低于32、25及300 nm,切削距离超过150 m后,工件表面粗糙度显著增大.机械摩擦作用、热化学作用及磨料磨损作用为导致金刚石刀具磨损的主要原因.     

DYNAMIC STRESS ANALYSIS OF GAS TURBINE ROTOR AIRFOILS USING THERMOELASTIC TECHNIQUES

The SPATE system provided a means for experimental ther-moelastic analysis of high frequency modes of vibration of a complicated turbine impeller which did not facilitate analysis with conventional methods due to low stress response and high modal density.
Testing also demonstrated a unique experimental stress analysis technique which was applied to a blade and vane airfoil and exhibited excellent stress distribution correlation with an established experimental technique (brittle lacquer) and with analytical stress distributions predicted by NASTRAN.
Full field dynamic stress analysis of gas turbine compressor airfoils accomplished using thermoelastic techniques provided an efficient method of determining optimum strain gage locations for monitoring rig and engine vibratory stress.
Significant cost savings could be realized using this technique from: (1) reduction in the amount of instrumentation required to characterize airfoil dynamic behavior and (2) increased vibratory response mode coverage thereby preventing the re-running of engine test programs to measure vibratory stress response levels of unexpected resonances encountered during initial engine testing.
Care is required when using SPATE results for vibratory modes resulting in high bi-axial stress distributions since the system output indicated stress magnitudes based on the sum of the principal stresses which could be significantly higher than either of the individual principal stresses.     

表面粗糙度对Glidcop和Q345低周疲劳寿命影响的试验研究

为考察表面粗糙度对弥散增强铜合金Glidcop和低合金钢Q345疲劳寿命的影响,对两种材料都加工了不同粗糙度等级的试样,在常温下进行了应力控制的低周疲劳试验,并对断后的试样进行了扫描电镜观察。结果表明,两种材料共有的现象是:粗糙表面削弱了低周疲劳性能,随着表面粗糙度的增大,低周疲劳寿命呈下降趋势;表面粗糙度对主裂纹的形成时间有影响。不同的现象是:低周疲劳寿命与表面粗糙度的关系Glidcop为线性,而Q345则为幂函数;Glidcop的断口有轻微颈缩,疲劳辉纹明显,Q345的主裂纹沿着试样的径向和周向同时扩展,大粗糙度下辉纹支离破碎。因此,表面粗糙度对疲劳寿命的影响既表现出共同的现象,又呈现为材料相关性。本文的结果将为这两种材料制成的承受低周疲劳构件的表面粗糙度选取提供参考。     

The Effect of Isopropyl Alcohol and Non-Ionic Surfactant Mixtures on the Wetting of Porous Coated Paper

The influence of isopropyl alcohol and non-ionic surfactant solutions on aqueous droplet wetting behaviour on porous coated paper was determined. Paper coatings provide a micro- and nano-porous surface structure, which strictly speaking cannot be described in simple roughness terms as sub-surface lateral absorption directly impacts on the apparent contact angle. It is this very deviation from an idealised system that leads to novel wetting phenomena. Isopropyl alcohol and surfactant-based systems, both of which are commonly used in the printing industry, show differences in wetting behaviour, on both short and long timescales, with changes in the relative composition of the mixtures. Small variations of 0.1?wt% in surfactant concentration have a dramatic influence on the dynamic surface tension, and thus the wetting. It was observed that the wetting kinetics for isopropyl alcohol and surfactant solutions were different in terms of both wetting area and the penetration rate, even in cases where the dynamic surface tension of the solutions was kept the same. Different stages in the wetting and following drying processes could be observed with near infrared spectral imaging. In addition, the surfactant chemistries such as their degrees of hydrophilicity and molecular weights generated comparative differences in the wetting kinetics. The dominating factor affecting the wetting was, as expected, the solid?Cliquid interfacial energy defined on the practical porous substrate, which differed from the direct comparison with dynamic surface tension, thus exemplifying the deviation from idealised surface roughness behaviour when considering porous materials. An apparent ??equivalent?? surface roughness value for the porous material was determined, and it was seen that an increase in this equivalent parameter enhanced the rate of wetting behaviour with decreasing solution surface tension, and so also affected the wetting evolution. The wetting was enhanced by cavities in the coating layer, which were enlarged by the penetrating liquids.     

Design and Modeling for Chatter Control

Boring bars for single-point turning on a lathe are particularly susceptible to chatter and have been the subject of numerous studies. Chatter is, in general, caused by instability. Clearly, the cutting process can be limited to regions of known stable operation. However, this severely constrains the machine-tool operation and causes a decrease in productivity. The more aggressive approach is to attack the stability problem directly through application of vibration control. Here, we demonstrate a new biaxial vibration control system (VPI Smart Tool) for boring bars. We present the experimentally determined modal properties of the VPI Smart Tool and demonstrate how these properties may be used to develop models suitable for chatter stability analysis, simulation, and development of feedback compensation. A phenomenological chatter model that captures much of the rich dynamic character observed during experiments is presented. We introduce the notion that the mean cutting force changes direction as the width of cut increases due to the finite nose radius of the tool. This phenomenon is used to explain the progression from chatter that is dominated by motions normal to the machined surface at small widths of cut to chatter that is dominated by motions tangential to the machined surface at large widths of cut. We show experimental evidence to support our assertion that a biaxial actuation scheme is necessary to combat the tendency of the tool to chatter in both directions. We then present some preliminary theoretical results concerning the persistence of subcritical instability as we expand consideration to high-speed machining.     

锻压操作机夹持长棒料随动过程动态受力分析

研究了锻压操作机夹持长棒料锻件锻压随动过程中夹钳的受力状态。利用拉格朗日方程及有限元方法建立了包含操作机及其锻件的总体动力学方程。操作机系统建立为端部悬挂质量弹簧的Euler-Bernoulli梁模型,随动过程中因为梁上节点位移激励引起操作机系统的瞬态振动。计算结果与LS-DYNA显式有限元模型结果进行了比对,吻合良好。结果表明,对于长棒料锻件,液压机锻压的位置对操作机的动态受力有着十分显著的影响。     

Analysis of Machining Stability for a Parallel Machine Tool

Abstract

Machine tool chatter is a self-excited vibration generated by chip thickness variation. It severely degrades the quality of the machined surface. The incidence of chatter is greatly affected by the dynamic characteristics of machine tool structure. This article extends chatter stability analysis to a machine tool equipped with a parallel mechanism. The vibration model of a parallel machine tool is derived, in which the legs of the parallel mechanism are considered as spring-damper systems. Then, the regenerative cutting dynamics is combined with the vibration model and stability analysis is performed. The chatter stability charts for various machining parameters are examined, with the example of the cubic parallel mechanism that is specially designed for machine tool use.     

薄壁件加工系统动态响应分析

薄壁件在铣削加工中容易产生共振或变形，直接影响加工稳定性及加工精度。采用主轴-刀具-工件整体铣削系统连续梁模型，系统研究在动态铣削力作用下，刀具端部与工件端部的动态响应之间的相互影响关系以及对整体系统动态响应影响较大的薄壁件尺寸。结果表明，工件横截面高度对系统共振的影响较为明显，当高度尺寸较小时，工件的低频共振会通过动态铣削力直接反映到刀具端部的振动频响上。工件横截面底边宽度尺寸的增大虽然对共振频率的改变不太明显，但会导致激发出来的刀具共振幅度出现明显降低。研究成果可以为薄壁件铣削加工系统的稳定性控制提供理论基础。     

Net shape manufacturing and the performance of polymer composites under dynamic loads

An experimental investigation was conducted to determine the influence of postmold trimming and resultant edge quality on the performance of fiber-reinforced plastics (FRP) under dynamic loads. Graphite/epoxy and graphite/bismaleimide laminates were machined using three state-of-the-art industrial techniques and subjected to three-point bend impact to failure. The load load-line displacement records were used to obtain the load, bend deflection and energy absorbed to fracture. High-speed photography was also employed to identify the initiation and progression of failure and record the time dependent fracture process. From a comparison of edge quality and subsequent material performance for both polymeric composites, it was found that the impact response of FRPs is highly process dependent. In general, the load and energy absorbed to fracture decreases with increasing surface roughness. Reductions in the load and energy to the onset of fracture with degrading surface quality were as high as 20 percent. The dynamic response was also found to be dependent on the constituents, stacking sequence and impact velocity.     

Simulation of soil compaction with vibratory rollers

The combination of a vibratory roller and soil represents a closed-loop system. For the reactions of this system, differences between reasons and effects cannot be stated separately. By means of modelling and simulation, the vibrating behaviour as well as the compaction effect of vibratory rollers is investigated. For the representation of the interdependencies between roller and soil during compaction a calculation model is developed, consisting of two models. One is an analytical model for the roller and the other is a model which describes the qualities of the soil, relevant to compaction. When defining the mathematical model, the non-linearities of roller motion and ground deformation are considered through a distinction between bounce and contact operation as well as between elastic and non-elastic ground deformation. Simulation results verify that the calculation model for the roller/soil system is suitable for mathematically determining the vibration behaviour and the compaction effect of the roller. The simulation accordingly permits the computer-based trial of closed loops to optimize automatically the constructional and operational roller parameters. Furthermore, the quality of goal-directed design of vibratory rollers can be enhanced before prototypes are built. Expensive iteration loops between design and experiment can, therefore, be avoided.     

附加约束阻尼层对星箭系统动特性的影响分析

在星箭连接支架外表面附加约束阻尼层可抑制星箭对接界面的振动,从而降低卫星在发射过程中所承受的振动和噪声载荷.本文将有限元技术与矩阵特征值摄动分析方法相结合,就卫星支架局部修改(附加约束阻尼层)对星箭系统动态特性的影响进行了分析.以已有星箭系统结构的模态信息为基础,给出了支架部位附加约束阻尼层后星箭系统动态特性变化的定量计算方法,并证明了该减振技术能够不明显的改变原星箭系统的固有特性.     

Ultrasonic-Assisted Dry Creep-Feed Up-Grinding of Superalloy Inconel738LC

Among many machining methods, grinding is the most applicable one for cutting hard-to-cut materials such as superalloys. In this research, effects of longitudinal ultrasonic vibration of workpiece (Inconel738LC) in dry creep-feed up-grinding process were investigated. Mechanism of abrasive grain and workpiece surface interaction and the consequences have been analyzed both analytically and numerically. Then, the results have been compared with experimental findings. Analytical calculations showed that there is a multiple and discontinuous cutting along the contact zone of grinding wheel and the workpiece when longitudinal ultrasonic vibration is used. Two-dimensional finite element modeling in commercial MSC.Superform software, showed the same behavior and results. Grinding forces are one of the major output parameters for evaluations. It was observed that, application of ultrasonic vibration can decrease grinding forces. A practical decrease of up to 27% of vertical grinding forces and up to 22% of horizontal grinding forces has been achieved when using ultrasonic vibration. Finite-Element analysis has shown a reduction of about 40% of grinding forces compared with ordinary grinding. Probable lower risks of thermal damage even for working under dry conditions can be a big advantage of using ultrasonic with grinding.     

MEASUREMENT OF ADHESION FORCES IN AIR WITH THE VIBRATION METHOD

The vibration method represents a practical method for the measurement of adhesion forces and adhesion force distributions. This method causes sinusoidally altemating stresses and yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an adhesion force intensification through flattening of asperities. The measuring principle of the vibration method and the analysis of experimental results are described in the article. Normal adhesion forces (pull-off forces) are measured using the vibration method and the colloidal probe technique. The results of both methods show good agreement for small particle sizes. The influence of the detachment force direction is shown by comparing tangential and normal adhesion forces measured using particle reentrainment in a turbulent air flow and the vibration method, respectively. The surface roughness of the substrate and the relative humidity are shown to significantly influence the measured adhesion forces. For the calculation of the adhesion forces, an approach by Rabinovich was combined with approximations of plastic micro asperity flattening. The Rabinovich approach accounts for roughness effects on the van der Waals force by incorporating the rms roughness of the interacting surfaces. rms-values of the particles and substrates were measured with atomic force microscopy at different scanning areas.     

A 6-DOF passive vibration isolator based on Stewart structure with X-shaped legs

By employing the nonlinear stiffness and damping characteristics of a bio-inspired X-shaped structure (XSS) with passive springs and the Stewart platform with six degrees of freedom, a passive 6-DOF vibration isolation platform is designed and experimentally studied for its vibration isolation performance. A three-layer asymmetrical XSS is adopted as legs to construct a passive Stewart platform. Because of the specially designed XSS, the stiffness and damping properties of the system can be adjusted by changing structural parameters and thus it is designable to achieve an excellent performance including excellent stability and high-static-low-dynamic-stiffness isolation effect in all six directions with satisfactory loading capacity in the vertical direction, without any active control. Analytical and extensive experimental analysis of static stiffness and vibration response of the system revealed that (a) the aXSS Stewart platform has very beneficial high static nonlinear stiffness which can provide sufficient loading capacity; (b) the platform can achieve very low dynamic stiffness in each direction without losing loading capacity; (c) both static and dynamic stiffness is adjustable and designable with structure parameters and very easy to implement in a pure passive manner.     

基于表面粗糙度影响的摩擦声发射特性研究

接触表面粗糙度是影响摩擦的重要因素之一,而摩擦为复杂的动态过程,在线测量非常困难.为了研究表面粗糙度对摩擦的影响,利用声发射技术对不同粗糙度表面的摩擦过程进行了检测.研究结果表明：摩擦系数随着表面粗糙度的增大而增大,但当粗糙度增至一定程度时,摩擦系数随着表面粗糙度的增大而减小;声发射信号各参数（振铃计数、振幅、能量）随表面粗糙度的变化规律与摩擦系数随粗糙度的变化规律一致;声发射信号各参数与表面粗糙度存在密切的对应关系,因此,用声发射技术实时监测摩擦过程是可行的.     

Mathematic modeling and characteristic analysis for dynamic system with asymmetrical hysteresis in vibratory compaction

We investigate dynamic characteristics of vibratory compaction system with asymmetrical hysteresis. An asymmetrical model derived from Bouc-Wen differential equation is employed to describe hysteretic behavior of vibration engineering. A practical polynomial expression for hysteretic restoring force is deduced to be substituted into standard equation of the system, assuming that the non-linearity of the restoring force is weak. An asymptotic method, which combines Krylov-Bogolyubov-Mitropolsky (KBM) method with harmonic balance (HB) method, is applied to analyze steady-state responses of the asymmetrical hysteretic system subjected to harmonic excitation. Dynamic responses, such as the restoring force time histories and frequency responses of the system for the first order approximate, are obtained. Furthermore, numerical solution obtained using Runge-Kutta method as well as results of experiments (asphalt compaction on the Beijing-Fuzhou highway) are compared with the asymptotic solution. These results investigated that asymmetrical hysteretic model and the methods applied in this paper are quite appropriate for engineering applications.     

Chatter mitigation using the nonlinear tuned vibration absorber

A passive vibration absorber, termed the nonlinear tuned vibration absorber (NLTVA), is designed for the suppression of chatter vibrations. Unlike most passive vibration absorbers proposed in the literature for suppressing machine tool vibrations, the NLTVA comprises both a linear and a nonlinear restoring force. Its linear characteristics are tuned in order to optimize the stability properties of the machining operation, while its nonlinear properties are chosen in order to control the bifurcation behavior of the system and guarantee robustness of stable operation. In this study, the NLTVA is applied to turning machining.