A numerical model of an oscillating squeeze film between a rubber surface and a rigid surface

A numerical model for the hydrodynamic behavior of an oscillating squeeze film between a rubber surface and a rigid surface is presented. The effects of roughness of the rubber surface on the hydrodynamic force and the leakage flow rate in the squeeze film are analyzed. A modified Reynolds equation, Laplace equation and a three-parameter viscoelastic constitutive equation are solved simultaneously to obtain the pressure distribution in the squeeze film and the deformation of the rubber surface. Equations are discretized into finite difference equations and solved by Gauss-Siedel iteration method. It is found that increasing roughness of the surface profile significantly increases the hydrodynamic force accompanied by a small decrease in the leakage flow rate. Spatial distribution of the roughness of the rubber surface has no significant effect on the leakage flow rate or hydrodynamic force. The results obtained from the presented simple model are compared with the experimental results available in the literature and a very good agreement is found.     

Viscoplastic incompressible flow of frictional-cohesive solids

A constitutive equation for the viscoplastic and incompressible flow of solids is presented. The equivalent viscosity includes cohesion, friction and fluidity parameters and is a non-linear function of both pressure and velocity. The model is employed in a steady-state flow formulation which is discretized by means of finite elements with velocities as nodal unknowns. Application is made to axisymmetric and two-dimensional gravity flow in hoppers, and the main parameters affecting the pressure distribution on the walls are identified. Results are compared with experiments and analytical models by other authors and show good agreement.     

Diffusion effects in hypersonic flows with a ternary mixture

An evaluation of multi-component diffusion effects in hypersonic flows is presented. A comparison is made of the results obtained from the common simplifying assumption of Fick’s law with the results obtained from the precise constitutive relations stemming from the kinetic theory of gases. To fix the ideas, the flow of a ternary mixture past a flat plate is considered, for which pressure diffusion is negligible. Whereas the precise analysis is more complicated, the results for the mass-fraction distribution can be significantly different from the corresponding simpler analysis stemming from Fick’s Law.     

Static and dynamic characteristics of externally pressurized circular step thrust bearings lubricated with couple stress fluids

The combined effects of couple stresses, fluid inertia and recess volume fluid compressibility on the steady-state performance and the dynamic stiffness and damping characteristics of hydrostatic circular step thrust bearings are presented theoretically. Based on the micro-continuum theory, the modified Reynolds equation and the recess flow continuity equation are derived by using the Stokes constitutive equations to account for the couple stress effect resulting from a lubricant blended with various additives. Using a perturbation technique, results in terms of steady-state load-carrying capacity, oil flow rate, stiffness and damping coefficients are presented. A design example is also illustrated for engineering and industrial applications.     

Note s on contributors

The applicability of time series modelling techniques to the simulation of machined surface profiles is discussed. The methods are then illustrated for a second-order autoregressive model with a normal amplitude distribution. In order to allow generation of non-normal surface profiles the relations between the surface height third moments and residual third moments together with similar relations for the fourth moments, and hence skew and kurtosis, are also given for first- and second-order autoregressive models. Examples are then shown for each of these cases.     

Wavelet transform based image template matching for automatic component inspection

In this study, empirical constitutive relations of materials with different crystalline structures through severe plastic deformation are introduced. Here, for each material, an optimized empirical relation is chosen by fitting some empirical relations on the results achieved from a dislocation-based constitutive model. In this work, four modes of empirical relations are fitted on the results of modified Estrin–Toth–Molinari–Brechet constitutive model for four materials with different crystalline structures (Al, Cu, Ta, and Zr). The obtained relations for the materials can be usable in commercial finite element codes.     

Computational evaluation of strain-rate-dependent deformation behavior of rubber and carbon-black-filled rubber under monotonic and cyclic straining

The molecular chain network model for elastic deformation behavior and the reptation theory for viscoelastic deformation behavior are used to derive a constitutive equation for rubber. The new eight-chain-like model contains eight standard models consisting of Langevin springs and dashpot to account for the interaction of chains with their surroundings. Monotonic and cyclic deformation behavior of rubber with relaxation under different strain rates have been examined. The results reveal the roles of the individual springs and dashpot, and the strain rate dependence of materials in the monotonic and cyclic deformation behaviors, particularly softening and hysteresis loss, that is, the Mullins effect, occurring in stress-stretch curves under cyclic deformation processes. The validity of the results is checked through comparison with experimental results. The deformation behaviors of a plane strain rubber unit cell containing carbon-black (CB) under monotonic and cyclic straining are investigated by computational simulation using the proposed constitutive equation and homogenization method. The results reveal the substantial enhancement of the resistance of CB-filled rubber to macroscopic deformation, which is caused by the marked orientation hardening due to the highly localized deformation of rubber. The role of strain rate sensitivity on such characteristic deformation behaviors as increases in the resistance to deformation, hysteresis loss, and the effects of the distribution morphology and the volume fraction of CB on the deformation behavior is clarified. The increases in the volume fraction and in the aggregation of the distribution of CB substantially raise the resistance to deformation and hysteresis loss.     

DESIGN METHOD OF MAGNETO- RHEOLOGICAL FLUID SHOCK ABSORBER FOR CAR SUSPENSION

The Bingham constitutive model, which is previously used in depiction of magnetorheological （MR） fluids rheological behaviors for design devices, exhibits discontinuous characteristics in representation of pre-yield behaviors and post-yield behaviors. A Biviscous constitutive model is presented to depict rheological behaviors of MR fluids and design automotive shock absorber. Quasi-static flow equations of MR fluids in annular channels are set theoretically up based on Navier-Stokes equations and several rational simplifications are made. And both flow boundary conditions and flow compatibilities conditions are established. Meantime, analytical velocity profiles of MR fluids though annular channels are obtained via solution of the quasi-static flow equations using Biviscous constitutive model. The prediction methodology of damping force offered by MR fluid shock absorber is formulated and damping performances are predicated in order to determine design parameters. MR fluid shock absorber for Mazda 323 car suspension is designed and fabricated in Chongqing University, China. Measurements from sinusoidal displacement cycle by Shanchuan Shock Absorber Ltd. of China North Industry Corporation reveal that the analytical methodology and design theory are reasonable.     

The influence of the viscoplastic and viscoelastic character of a lubricant on elastohydrodynamic lubrication

The non-newtonian constitutive equation proposed by Johnson and Winer is discussed. Derivations of the lubrication equations suitable for the viscoplastic rheological model and the viscoelastic model are presented. The full numerical elastohydrodynamic lubrication solutions for the viscoplastic model and the viscoelastic model are obtained in order to observe the effects of the elastic shear modulus of the fluid and the limiting shear stress on the pressure distribution, film thickness and coefficient of friction.     

基于fluent的气体止推轴承出口性能仿真与分析

采用基于有限体积法的流体动力学软件fluent,仿真气体轴承气膜出口处的压力分布,并对层流模型和湍流模型仿真的结果进行对比。在用湍流模型仿真时,对比理想光滑壁面和粗糙壁面的仿真结果,分析了壁面粗糙度对气体轴承性能的影响,同时fluent仿真的结果也有效地验证了传统数值仿真时为简化模型所做的一系列假设都是合理的。     

NONLINEAR DYNAMIC BEHAVIOR OF VISCOELATIC TPANSMISSION BELT

The nonlinear dynamic responses of viscoelastic axially transmssion belts are investigatedand the Kelvin viscoelastic differential constitutive model is employed to characterize the materialproperty of belts. The generalized equation of motion is obtained for a viscoelatic axially transmissionbelts with geometric nonlinearity first, and then is reduced to be a set of second-order nonlinear ordi-nary differential equations by applying Galerkin's method. Finally the effects of viscosity parameterand elastic parameter and the moving velocity of the belts on the transient responses are investigatedby the research of digital simulation.     

Vibration of functionally graded cylindrical shells

Functionally gradient materials (FGMs) have attracted much attention as advanced structural materials because of their heat-resistance properties. In this paper, a study on the vibration of cylindrical shells made of a functionally gradient material (FGM) composed of stainless steel and nickel is presented. The objective is to study the natural frequencies, the influence of constituent volume fractions and the effects of configurations of the constituent materials on the frequencies. The properties are graded in the thickness direction according to a volume fraction power-law distribution. The results show that the frequency characteristics are similar to that observed for homogeneous isotropic cylindrical shells and the frequencies are affected by the constituent volume fractions and the configurations of the constituent materials. The analysis is carried out with strains–displacement relations from Love’s shell theory and the eigenvalue governing equation is obtained using Rayleigh–Ritz method. The present analysis is validated by comparing results with those in the literature.     

板材热轧热力耦合有限元模拟

建立了三维热力耦合问题弹塑性有限变形有限元方法,并对板材热轧过程进行了计算机模拟。材料流动应力模型中考虑了应变历史、应变速率和温度的影响,导出了与其相应的本构关系矩阵。应用该方法可以给出轧件变形过程中诸如温度场、应变场和应变速率场等各种热力结果。算例表明,该方法具有较好的精度。     

Use of crystal plasticity in metal forming simulations

Some recent work on the implementation of crystal plasticity constitutive relations in the simulation of metal deformation processes is discussed. The rate-dependent crystal plasticity theory employed is first briefly presented. We then consider some special cases of fcc metals with certain “ideal textures”, for which closed-form analytical solutions are given for rolling and biaxial sheet stretching modes. Finally, the incorporation of the crystal plasticity constitutive relations into the finite element analysis of large-strain boundary-value problems is illustrated. The example treated is the behaviour of axially constrained and freely elongating solid circular bars subject to finite strain torsion.     

AN ANALYTICAL MODEL OF OBLIQUE CUTTING WITH APPLICATION TO END MILLING

A new analytical cutting force model is presented for oblique cutting. Orthogonal cutting theory based on unequal division shear zone is extended to oblique cutting using equivalent plane approach. The equivalent plane angle is defined to determine the orientation of the equivalent plane. The governing equations of chip flow through the primary shear zone are established by introducing a piecewise power law distribution assumption of shear strain rate. The flow stress is calculated from Johnson-cook material constitutive equation. The predictions were compared with test data from the available literature and showed good correlation. The proposed model of oblique cutting was applied to predict the cutting forces in end milling. The helical flutes are decomposed into a set of differential oblique cutting edges. To every engaged tooth element, the differential cutting forces are obtained from oblique cutting process. Experiments on machining AISI 1045 steel under different cutting conditions were conducted to validate the proposed model. It shows that the predicted cutting forces agree with the measurements both in trends and values.     

Three-dimensional modeling of roughness effects on microthickness filling in injection mold cavity

Effects of cavity surface roughness on filling polymer flow in macrocavities are generally not significant. However, in a microcavity, surface roughness may become very important and ignoring it could lead to inaccurate or even misleading results. As an extension to our previous work, a three-dimensional roughness model for filling polymer flow in microinjection molding is proposed that takes into consideration the cavity surface roughness effects. A numerical procedure, which implements the finite volume and level set methods and integrates the proposed roughness model, is presented. The numerical model was validated by comparing its predicted results with experimental and/or analytical results. The numerical results obtained using the three-dimensional roughness model were in good agreement with experimental observations and were more accurate than those obtained using the two-dimensional roughness model.     

Static pressure recovery analysis in the vane island diffuser of a centrifugal pump

The overall performance of a vane-island type diffuser of a centrifugal pump model was obtained by means of directional probe traverses. These measurements were performed in an air model of a real hydraulic pump for five volume flow rates. Directional probe traverses are performed with a classical three-hole probe to cover most of the complete inlet section of the diffuser from hub to shroud and from pressure to suction side. Existing Particle image velocimetry (PIV) measurement results are also used to compare probe measurement results between the inlet and outlet throats of vane island diffuser at mid-span. Some assistance from already existing unsteady calculation, including leakage effects, is used to evaluate the numerical approach capability and to correctly define the mean initial conditions at impeller’s outlet section. Pressure recovery and the measured total pressure loss levels inside this particular vane diffuser geometry are then calculated. Detailed analysis of the flow structure at the inlet section of the vane island diffuser is presented to focus on pressure evolution inside the entire diffuser section for different flow rates. The combined effects of incidence angle and blockage distributions along hub to shroud direction are found to play an important role on loss distribution in such a diffuser.     

超高压水射流作用下岩石损伤破碎机理

由于水射流的高紊动与岩石材料的复杂性,水射流作用下岩石破坏机理的研究一直都是难点问题。运用全解耦流固耦合理论,建立超高压水射流冲击岩石介质的数值分析模型,射流采用标准k－ε模型和控制体积法,岩石采用线弹性和有限元法,计算分析淹没条件下岩石介质在水射流冲击作用下内部的应力分布规律。其次,根据岩石介质内部应力分布特征,基于岩石微元强度遵循Weibull分布的概率理论,将Mohr-Coulomb破坏准则作为随机分布变量,建立岩石损伤变量演化方程和连续损伤统计本构模型及用量纲一破坏系数来表征岩石破坏的准则。再次,按建立的流固耦合分析模型、岩石损伤模型和破坏准则,运用分阶段法对水射流的破岩过程进行了数值分析。最后,运用扫描电镜对水射流切割岩石断口形貌进行观测试验,分析岩石在超高压射流作用下微观破坏机制,主要有穿晶断裂和剪切错动两种形式,进一步验证数值模拟分析的结果,建立起水射流破岩过程中岩石微观破坏机制和宏观断裂分析的桥梁。     

Experimental study of porous foil bearings for web-handling

In this paper, new type of hybrid porous foil bearings for web-handling is presented, in which the traveling web is supported by the externally pressurized porous foil bearings with the hybrid effects of hydrodynamic pressure, due to web movements, and hydrostatic pressure, due to pressurized, added flow through the hollow porous shaft. The relations between web spacing height (air film thickness) and web traveling velocity are measured under various supply pressures. Moreover, the relations between web spacing height and web tension are examined. From these measured relations, the hybrid effects of porous foil bearing on the web spacing height characteristics are clarified experimentally, and it is concluded that the hybrid porous foil bearings presented here have an advantage of controlling the web spacing height to keep suitable web-handling conditions.