Showing papers in "International Journal of Applied Mechanics and Engineering in 2002"

Wear resistance of experimental Ti-Cu alloys

Abstract: After using cast titanium prostheses in clinical dental practice, severe wear of titanium teeth has been observed. This in vitro study evaluated the wear behavior of teeth made with several cast titanium alloys containing copper (CP Ti+3.0 wt% Cu; CP Ti+5.0 wt% Cu; Ti-6Al-4V +1.0 wt% Cu; Ti-6Al-4V+4.0 wt% Cu) and compared the results with those for commercially pure (CP) titanium, Ti-6Al-4V, and gold alloy. Wear testing was performed by repeatedly grinding upper and lower teeth under flowing water in an experimental testing apparatus. Wear resistance was assessed as volume loss (mm(3)) at 5kgf (grinding force) after 50,000 strokes. Greater wear was found for the six types of titanium than for the gold alloy. The wear resistance of the experimental CP Ti+Cu and Ti-6Al-4V+Cu alloys was better than that of CP titanium and Ti-6Al-4V, respectively. Although the gold alloy had the best wear property, the 4% Cu in Ti-6Al-4V alloy exhibited the best results among the titanium metals. Alloying with copper, which introduced the alpha Ti/Ti(2)Cu eutectoid, seemed to improve the wear resistance.

Flow of a second order/grade fluid due to non-coaxial rotation of a porous disc and the fluid at infinity

Abstract: The magnetohydrodynamic (MHD) flow of an electrically conducting second order/grade fluid past a porous disk is studied when the disk and the fluid at infinity rotate with the same angular velocity about non-coincident axes. It is found that the existence of solutions is in connection with the sign of the material modulus α1 for both suction and blowing cases. The effects of all the parameters on the flow are carefully examined.

Experimental behaviour of end plate i-beam to concrete-filled rectangular hollow section column joints

Abstract: An experimental study performed at the Civil Engineering Department of the University of Coimbra, Portugal is described in this paper The study consists of a series of six tests on extended and flush end plate connections, with one or two bolt rows in tension, loaded under monotonic conditions Provided is a description of the tested geometries, along with test setup, load application method and the specimens instrumentation Additionally, some of the available results are presented, with a focus on the joint moment-rotation response

Thermohydrodynamic study of misaligned plain journal bearings - comparison between experimental data and theoretical results

Abstract: Hydrodynamic journal bearings are essential components of high speed machinery. Under severe operating conditions, manufacturing defects or thermal distortions may induce running problems such as misalignment. The aim of this paper is to present a realistic numerical model in order to predict the misaligned plain journal bearing performance under steady-state conditions. Therefore, a three-dimensional thermohydrodynamic (THD) analysis has been developed and the predictions obtained with the proposed numerical model are validated by comparison with measurements carried out on our test device.

Computational modeling of nitric oxide formation in biomass combustion

Abstract: Nitric-oxide formation from fuel-bound nitrogen in turbulent non-premixed flames is investigated. The calculations are performed using the k-ε-model for turbulence and the Eddy Dissipation Concept for turbulent combustion in conjunction with detailed chemistry from GRI-Mech 2.11. Comparison with previously measured data shows that the radial profiles for nitric oxide are spread inaccurately, but yields negligible discrepancies for integrated values. Furthermore, to illustrate the potential of the model, preliminary simulations of a wood stove have been performed. Introduction Emission of nitric oxides (NOx ) from combustion processes is a serious threat to our environment. NOx is the main source of acid rain, ground-level ozone, and photochemical smog. NOx can be formed by heating air to a high temperature. This is usually the main source of NOx when oil or natural gas is burned, due to very high peak temperatures. Although peak temperatures typically are low in biomass and coal combustion, NOx emissions from burning of these fuels are very high since nitrogen is bound to the fuel. From a computational point of view, biomass combustion presents challenges such as pyrolysis and gasification of solid material, heterogeneous and homogeneous chemical reactions, radiation heat exchange, interaction between solid material and the turbulent reacting flow, interaction between turbulence and combustion, between heat exchange and gasification rate, etc. By gasification, fuel-bound nitrogen is mainly released in the form of hydrogen cyanide (HCN) and ammonia (NH3). If these components take part in combustion with excess air, the main part is transformed to nitric oxides. This paper describes an ongoing work to develop a mathematical model for quantitative prediction of NOx from nitrogen-containing fuels. Here, the focus is on the gas-phase reactions. The mathematical model is implemented in a CFD code capable of predicting flow and combustion processes in actual combustion equipment. This CFD tool will be used to develop improved combustion devices, such as low-NOx wood stoves. In the next section, the mathematical model is described. Then, in the third section, the model is compared with detailed measurements for a jet flame with carefully prescribed boundary conditions. In the section following that, simulation results from an actual wood stove are presented to illustrate the practical potential of the approach. Conclusions and recommendations for further work are given in the final section. Method and models The turbulent reacting flow was modeled by the mass-weighted Reynolds-averaged conservation equations for momentum components (the summation convention applies to the spatial indices), ∂ ∂t (ρ̄ũi ) + ∂ ∂x j (ρ̄ũi ũ j ) = − ∂ p ∂xi + ∂ ∂x j ( τ i j − ρu i u ′′ j ) , (1)

A contribution to the optimal choice of the HCR-gears regarding frictional losses

Abstract: High transverse contact ratio (HCR) gears are non-standard involute gears with a transverse contact ratio ea > 2 which proved adequate for use in automobiles, trucks, aircrafts and ships. The paper deals with the dependence of the sliding friction losses on HCR spur gears geometry: pressure angle, tooth height, gears centre distance resp. addendum modification coefficients sum, addendum modification coefficients sum distribution and other parameters. The calculations are based on the comparison between the values of the sliding friction loss geometrical factor, which comprises the influence of the magnitude and form of the toothing. A proper choice of these parameters is necessary for achieving good gearbox efficiency. The results of the calculations are shown in diagrams that can be a tribological guideline for the designer to choose gears optimal geometrical parameters.

Establishment of a new class of wear: adhesion initiated catastrophic wear

Abstract: The nucleation mechanisms and early stages of four types of catastrophic wear (CW), which can be identified as adhesion-initiated (AI) are considered. Close connections are established: a) between two low-energy types of AICW and a disclination mode of plastic deformation and between two high-energy types of AICW and an amorphous mode of plastic deformation, b) between the incidence of either type of low-energy AICW and the hardness of an AICW seed domain relative to that of the friction surfaces, and c) between the onset of AICW and a competitive stripping and reformation of interlayers. Hypothesis on generation and transfer of energy and heat at microlevel (in process of movement of dislocations and disclinations) is developed as a base of amorphous deformation. Attention is drawn to a need for further consideration of terminology in this field.

Lubrication in helical gears

Abstract: In this paper, a method to determine elastohydrodynamic film thickness in helical gears is developed by combining the Dowson-Higginson elastohydrodynamic lubrication (EHL) formulation with helical gear geometry and kinematics. Comparisons are made with traditional gear film thickness models. This analysis is then used to characterise the film thickness and lambda ratio in an automotive planetary gearset. Methods to measure surface roughness in fine-pitch gears are described.

An asperity based model for friction in mixed lubrication

Abstract: We propose a model for mixed lubrication between parallel surfaces. To do such, we first analyze the microgeometry. We determine a statistical distribution for asperity height and radius. Drawing upon these geometric parameters we identify the main mechanism available on a given asperity. wherefrom we deduce the individual normal and friction forces. The five possible mechanisms are isoor piezo-viscous hydrodynamic, elastohydrodynamic, elastoplastic and full plastic. By association of the results obtained for each asperity, we derive the mechanical behaviour for the entire contact. Several numerical applications are proposed. Theoretical results show the influence of the main contact parameters. They strongly agree with experimental results and theoretically confirm the master curve obtained by plotting the evolution of the friction coefficient versus the ηV p parameter with respect to a given pair of materials and their microgeometry.

Complete isothermal solution for the viscous regime of concentrated contact traction

Abstract: The viscous regime of EHL traction determines the mechanical losses in gears and other concentrated contacts at moderate pressures and high temperatures. Central film thickness may be calculated from measurements of viscosity as a function of pressure (to about 0.4 GPa) with sometimes a correction for non-Newtonian behavior [1]. Traction calculation, on the other hand, requires for the viscous regime, measurements of viscosity to the Hertz pressure and measurement of the ratio of shear stress to pressure for which cohesive failure occurs. A small correction is sometimes required for non-Newtonian (shear-thinning) behavior as well.

Optimum design for porous metal bearing

Abstract: Porous metal bearings as a specially sort of sliding bearing are common in use today in most of machines. Their main characteristic is possibility of selflubrication during operating life. The aim of this paper is to apply already developed basic concept for optimum design of sliding bearings generally on this sort of selflubricating porous metal bearing and make their optimum design study. The study makes objective functions and some equality and inequality constrains based on hydrodynamics lubrication theory. For this optimum design problem coefficient of friction is a main cost function and different design variables are defined depends on kind of optimisation. The optimum design model and procedure are realised through developed computer programme followed by numerical example and results analysis.