R.G. Bayer

Aerosol particle deposition in an obstructed turbulent duct flow

Abstract A computational scheme for simulating aerosol particle dispersion and deposition in turbulent flows in passages with complex geometry is developed. A thermodynamically consistent rate-dependent algebraic stress model is used to simulate the mean turbulent flow fields. The instantaneous turbulence fluctuation is simulated as a continuous Gaussian random field. The Brownian motion is modeled as a white noise process. The particle equation of motion including the Stokes drag, Brownian and Saffman forces is used. The computational model predictions for particle deposition velocity in a turbulent channel flow are compared with the experimental data and earlier simulation results. Several digital simulations for aerosol particle transport and deposition in a duct with an obstructing block are performed. The corresponding capture efficiencies of rectangular and trapezoidal blocks for different particle Stokes number are evaluated and discussed. It is shown that the deposition rate decreases significantly as the shape of the obstruction becomes more streamlined.

The influence of surface roughness on wear

Abstract A series of wear experiments utilizing a ball-plane configuration was performed to determine the influence of both the magnitude and anisotropy of the surface roughness on wear. It was found that: (1) wear increases with increasing roughness up to ~ V16 finish and remains relatively constant above that roughness and (2) sliding perpendicular to the lay increases wear above that for sliding parallel, with the difference becoming negligible for the finer roughness. A method of analytically relating the results obtained for ball-plane geometry to other geometries is developed.

Engineering model for wear

Abstract The wear produced between two metallic bodies sliding relative to each other has been correlated with stress. The results of 1,200 tests for various combinations of materials and lubricants have shown that wear can be eliminated for a given amount of time if the shear stress is kept below, a certain fraction of the yield point in shear of the weaker of the two metals. It has been shown that this fraction is a function of the materials and the lubricant used. Values of this fraction have been determined for a large number of combinations of materials.

Experimental investigation of dust particle deposition in a turbulent channel flow

Abstract An experimental set-up was designed, constructed, and used to study the wall deposition rate of particles in a turbulent channel flow. Deposition velocities for two classes of particles, namely, spherical glass particles with diameters of 5–45 μm, and five compact dust components in the size range of 1–10 μm were studied. The particle concentration at the test section was measured with the aid of an isokinetic probe. The particles were deposited onto a flat gold plate covered with a thin film coating. The coating was used to reduce the effect of particle bounce from the surface. The statistics of deposited particles were analyzed by an image processing technique which counts and sizes the particles. The deposition rate of spherical particles was found to increase with diameter. The deposition velocities for compact dust components were found to closely resemble those of equivalent spherical particles. The measured deposition velocities were in good agreement with the available experimental data and the empirical model.

Impact wear testing machine

Abstract An impact testing machine has been built to aid in the study of wear occurring on surfaces of repetitively loaded solid bodies. In this testing machine, bullet-shaped projectiles are bounced against a metal surface which is either stationary or rotating about an axis parallel to the approach of the projectiles. Wear can occur on both the projectile and on the surface it strikes, and both may be measured; however, unless impacts are synchronized, observation of progressive wear must be restricted to the projectile surface. These measurements made on the bullet surfaces yield information on “one-body wear”. The rotation of the impacted medium is expected to facilitate a study of the relative importance of sliding when the relative approach of the two bodies has a tangential as well as a normal component. In this paper the testing machine is described, and some typical photographs of impacted specimens are shown at various stages of wear.

Particle detachment mechanisms from rough surfaces under substrate acceleration

Particle removal mechanisms due to an accelerating substrate from rough surfaces are studied. The rough surface is modeled by asperities all of the same radius of curvature and with heights following a Gaussian distribution. The Johnson-Kendall-Roberts (JKR) adhesion model is used and the procedure for analyzing the particle pull-off force is described. The theory of critical moment, in addition to the sliding and lifting detachment models, is used, and the critical substrate accelerations for particle removal are evaluated and discussed. The model predictions for aluminum and glass particles are also compared with the experimental data and reasonable agreement is observed. The application of the results to surface-cleaning equipment is discussed.

Prediction of wear in a sliding system

Abstract In previous publications, the author and his co-workers have presented two models concerning wear prediction in sliding systems. The first model, the zero-wear model, enables one to predict analytically the amount of sliding required to produce wear of the order of the surface finish. The second model, the measurable-wear model, enables one to predict how wear, which is greater than the surface finish, will increase with increasing amounts of sliding. With the model for measurable wear, however, it was not possible to predict analytically how the wear would depend on other parameters of the system ( e.g. , load, material constants, etc.). This paper explores the possibility of using the zero-wear model, in conjunction with the measurable-wear model, to predict these dependencies. The results of this combined model were compared with experimental data obtained for several different sliding systems; good agreement was found between the theoretical calculations and experimental data.

On the significance of surface fatigue in sliding wear

Abstract An electron microscope study of wear damage produced by sliding on a copper single crystal indicated the significance of surface fatigue in wear resulting from sliding under low stress conditions. This paper describes the study and shows some comparisons between the results of this study and an engineering model for wear previously proposed.

Abrasive wear by paper

Abstract An engineering study of wear produced by data processing card stock is presented. Wear data was obtained for several different metals and geometries as well as for different loads and sliding speeds. These data were accumulated for amounts of sliding, from a few thousand feet of paper up to hundreds of miles. In addition, a model is proposed to explain some of the observed dependencies.

Influence of oxygen on the wear of silicon

Abstract The results of a series of wear tests on semiconductor silicon chips are presented. In these tests, hemispherical anodized aluminum sliders rubbed against flat silicon specimens with a small-amplitude oscillatory motion. The influence of several parameters, including the load, the slider roughness, the type of anodization, the contact geometry, the environment and the initial condition of the silicon surface, on the wear of the silicon was studied. Of these the influences of the environment and the initial condition of the silicon surface were most pronounced. It was concluded that oxide formation and growth on the silicon were important factors in the wear of the silicon and tended to increase the wear. It was also concluded that the primary wear mechanism of the silicon for low load is probably delamination or surface fatigue.