摘要:

Scanning electron microscope studies were conducted to characterize the erosion resistance of polymethyl methacrylate (PMMA), polycarbonate (PC), polytetrafluorethylene (PTFE), and ultra-high-molecular-weight polyethylene (UHMWPE). Erosion was caused by a jet of angular microparticles of crushed glass at normal incidence. Material built up above the original surface on all of the materials. As erosion progressed, this buildup disappeared. UHMWPE was the most resistant material and PMMA the least. The most favorable properties for high erosion resistance were high values of ultimate elongation, maximum service temperature, and strain energy and a low value of the modulus of elasticity. Erosion-rate-versus-time curves of PC and PTFE exhibited incubation, acceleration, and steady-state periods. PMMA also exhibited a deceleration period, and an incubation period with deposition was observed for UHMWPE. The material removal mechanism appeared to be similar to those for metals. Angular, cut-faceted surfaces, indicative of cutting wear, were observed. There was evidence of surface melting, which is believed to be the result of heat generated by impingement. Erosion due to spherical and angular particles was compared, and the optical transmittance characteristics were discussed. Erosion volumes are presented as functions of the depth, width, and width-depth ratio of the pit. These plots, unlike those for metallic materials, suggest two different trends. A power-law relation is presented to estimate the erosion rate.Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

ISSN:0569-8197    

DOI:10.1080/05698198608981688

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

It has been previously reported in the literature that a particular, unnamed, phosphonate antiwear additive can enhance elastohydrodynamic film thicknesses on rolling metal surfaces at elevated temperatures. In this paper, several different pure phosphonate additives have been prepared and their performance in rolling contacts has been studied. All the phosphonates tested formed thick films from base oil solution in rolling EHD contacts. The rate of film formation varied with the alkyl or aryl groups present and with the temperature but, in some cases, films started to form at room temperature. These films grew steadily with running over several hours, to reach thicknesses of more than one-half micron, augmenting the normal elastohydrodynamic films by this amount.

ISSN:0569-8197    

DOI:10.1080/05698198608981689

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The phosphonate esters shown in Part I to form thick chemical films in elastohydrodynamic contacts have been found to form a viscous reaction product when heated with iron powder. Both this viscous material and also the thick films formed in earlier elastohydrodynamic tests have been analyzed by a variety of chemical techniques and shown to be similar. They appear to consist of iron-phosphate-monoester polymer, with the phosphate acting as a bridge between iron (III) species. This structure is comparable to that observed in metal phosphinate polymers.Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

ISSN:0569-8197    

DOI:10.1080/05698198608981690

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In a numerical model of sliding friction, it is found that surface melting of the rotating band usually occurs before the system has travelled one bund length. Once melting had initiated, it was found that limiting the surface temperature to the melting temperature allowed the coefficient of friction to be found as a dependent parameter. The resulting coefficients of friction agree reasonably well with those found experimentally for rotating bands, particularly if residual heat in the tube is allowed for. The discrepancy between field tests and laboratory tests with pin-disk machines is explained on a basis of insufficent size or pressure to achieve local melting.Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

ISSN:0569-8197    

DOI:10.1080/05698198608981691

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A numerical solution in two dimensions of thermal effects in steady-state sliding confirms Blok's original analysis. It is shown that for transient sliding (assuming sudden contact), surface temperatures of about 50 percent of the steady-state value are reached in one sliding width of a contact patch and 80 percent in ten widths. If voids or singularities exist close to the surface in the moving body, transient surface temperatures easily exceeding the Blok steady-state value can occur.

ISSN:0569-8197    

DOI:10.1080/05698198608981692

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Some vendors and many users of rotating machinery are arbitrarily reducing the bearing damping by as much as 75 percent in order to accurately predict the location of the first and second lateral critical speeds. This paper shows that if the bearing support flexibility is considered, accurate critical speed predictions are possible without reducing the bearing damping. The equations for the equivalent support stiffness and damping are given for a flexible support spring, mass, and damper in series with the fluid film stiffness and damping properties of a tilting-pad bearing. These equations can easily be incorporated with any synchronous response and/or stability computer program. Examples of test stand results for four production rotors are shown illustrating the accuracy of this method.Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

ISSN:0569-8197    

DOI:10.1080/05698198608981693

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The lift-off distance between two nominally flat seal ring surfaces immersed in lubricant oil was measured at various sliding speeds using electrical resistance. Lift-off appeared very gradual, requiring 20∼50 minutes to stabilize, depending on the degree of truncation of asperities on the wearing surface.

ISSN:0569-8197    

DOI:10.1080/05698198608981694

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The abrasive wear resistance of cutting tool materials was found to be related to the properties of fracture toughness and hardness. This study has shown that the abrasive wear resistances of three classes of tool materials, brittle, brittle-ductile, and ductile, are controlled by the specific response of each material to the abrader.

ISSN:0569-8197    

DOI:10.1080/05698198608981695

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Experimental observations on unpressurized dynamically loaded hydrodynamic bearings and squeeze-film dampers indicate that cavitation bubbles, once formed, do not completely redissolve upon the reappearance of positive pressures. Instead, one is left with a spongy compressible fluid. Assuming this to be a homogeneous gas-liquid mixture, with density and viscosity dependent on pressure, the load capacity of squeeze-film dampers is compared with that obtained using hitherto adopted cavitation models which assume an incompressible lubricant with the fluid-film pressures being set to the saturated vapor pressure (SVP) of the lubricant whenever the pressure falls below the SVP. To save computation effort, a short bearing approximation is derived for the compressible Reynolds equation, so that comparisons apply to narrow dampers only (i.e. to dampers with length-to-diameter ratios less than 0.25). It is shown that for circular orbit squeeze-film dampers, best agreement is obtained with the incompressible model where the SVP is taken as zero absolute, though depending on the orbit eccentricity and the value of a dimensionless parameter called the squeeze number, commonly used π and 2π film cavitation models may also give excellent agreement.Presented at the 40th Annual Meeting in Las Vegas, Nevada May 6–9, 1985

ISSN:0569-8197    

DOI:10.1080/05698198608981696

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Theoretical cavitation models previously adopted in analyzing dynamically loaded hydrodynamic bearings or squeeze-film dampers are inconsistent with experimental observations in that bubbles, once formed, in many instances do not completely redissolve upon the reappearance of high pressure. A more representative approach could be to model the lubricant as a homogeneous two-phase gas-liquid mixture. The density and viscosity of such a homogeneous mixture are developed as functions of the pressure and the known mole fraction of the noncondensable gas to the liquid at supply entry. Omitting the possible effects of surface tension, it is shown that if the vapor pressure of the lubricant is of the order of 10−3atm or less, it has only a minimal effect on the density of the mixture and may be ignored. On the other hand, solubility effects may be significant, though it is unknown to what extent gases, once drawn out of solution, will redissolve in the short time of the cycle period of the dynamic loading.

ISSN:0569-8197    

DOI:10.1080/05698198608981697

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor