Glass and stainless steel substrates produced distinctly different frictional behavior, especially in dry and humid environments. All dry interactions with the exception of rough glass-on-glass exhibited a significant increase in mean friction relative to measurements at ambient humidity; this effect was most prominent on stainless steel substrates and became progressively stronger for smoother stainless steel substrates.
INTRODUCTION
Static friction data consists of a single point corresponding to a specific contact event, whereas dynamic friction measurements enable the analysis of a larger area over a longer duration. Thus, dynamic friction measurement produces a much more powerful data set for analysis, although it requires a more complex setup to obtain these measurements, more sophisticated data processing and analysis, and it provides the added challenge of understanding effects that may affect not only sample-to- sampling variability, but temporal and spatial variability within a single sample.
LITERATURE SURVEY AND BACKGROUND
2 mm average, a measure of the average coefficient of friction over the previous 2 millimeters/24 test points. 2 mm standard deviation, a measure of the standard deviation of the coefficient of friction relative to the previous 2 mm/24 test points. The stainless steel substrates consistently showed an increase in mean friction over the duration of the test.
This suggests that there was significant mechanical change of the stainless steel surfaces under these conditions. There were no signs of surface cracking or other glass damage in this part of the glass. The most plausible explanation for this phenomenon is the thermal mass of the stainless steel substrates.
Furthermore, the friction behavior of the borosilicate glass samples was significantly different from the other specimens. This behavior is also consistent with a second observation by the same team that was borosilicate glass. Furthermore, microscopy of the stainless steel samples revealed material removal and visible ductile deformation of the stainless steel surfaces.
FRICTION THEORY AND ITS ORIGINS
CONTACT THEORY AND ADHESION
As mentioned by Johnson7, the first attempt to mathematically define the contact area between two bodies was by Heinrich Hertz, after whom the fundamental contact theory is named. The crucial, fundamental aspect of the JKR theory is the integration of surface energy and the resulting holding force in predicting the contact area between two elastic solid surfaces.
HEAT TREATMENT AND SURFACE PREPARATION
Surface energy is a measure of a surface's reactivity: compared to lower energy surfaces, high energy surfaces have a greater amount of chemically active groups with the potential to form bonds or otherwise interact with other surfaces. In practice, the static coefficient of friction reached a maximum of approx. 0.7 after a heat treatment cycle of 60 minutes at 300C.
HUMIDITY AND FRICTION
Subhi, Fukuda, Morita, and Sugimura found that the thickness of the adsorbed water film on a 316 stainless steel surface varies from <1 nm at 3% RH to ~30 nm at moderate humidity, up to 60 nm near saturation. The authors conclude that this sharp drop in adhesion occurred because the height of asperities on the glass surface exceeded the thickness of the adsorbed liquid film, thereby reducing the effective contact area of the water film and thus its contribution to the adhesive forces.20.
WEAR/SURFACE EFFECTS AND FRICTION
This deformation will occur when the local stress on a material exceeds the yield stress of the material, and asperities will flatten out under shear, increasing the effective contact area between surfaces. As friction continues, this process can eventually be negated by the formation of debris, resulting in a coarsening of the effective surface topography.23 This is consistent with the work of Godfrey and Bailey, who tested and observed friction between glass and copper that friction initially increased. from 1.2 to 1.6 before gradually decreasing to a value near 0.5.
ROUGHNESS, FRICTION/ADHESION, AND WEAR
For both glass compositions, the samples had similar friction at the beginning of the test, but after extensive wear, the rougher pins had a higher overall coefficient of friction. The authors observed a corresponding roughening of the smooth sample and a softening of the rougher sample during testing.31.
SURFACE FINISHING OF GLASS AND STEEL
EXPERIMENTAL PROCEDURES
CONDITIONS/SAMPLE DESIGNATIONS
SAMPLE ACQUISITION/PREPARATION
Glass and Stainless Steel Specimens
The aluminosilicate and soda lime samples were 50 mm x 50 mm; the borosilicate samples measured 25 mm x 75 mm.
Surface Roughening Processes
Thermal Treatment
COEFFICIENT OF FRICTION TESTING
The parts were cooled for a minimum of ten minutes before starting the friction test. Nitrogen or air of the desired humidity was supplied to the box at a minimum rate of 4 cubic feet per minute. During the friction coefficient test, the sled was pulled over the substrate at a continuous speed of 50 millimeters per minute.
Standard deviation of means, a measure of the amount of sample-to-sample variability for a particular condition. Coefficient of Variation (COV): This metric is calculated at the sample level by dividing the standard deviation metric by the average friction coefficient for a given sample.
CONTACT ANGLE MEASUREMENT
SURFACE ROUGHNESS MEASUREMENTS
EXPERIMENTAL RESULTS
SURFACE ROUGHNESS
The surface roughness of the coated samples was uniform across all measurements on all parts and there was no evidence of local areas or individual samples deviating significantly from this. The electropolished stainless steel samples used for this experimentation are particularly noteworthy as they have not been adequately characterized by conventional. While the measured surface roughness values for electropolished steel are comparable to those for stainless steel no. 3, it is clear from the surface topography images that Ra, rms and PV measurements do not adequately quantify the effect of electropolishing on stainless steel surfaces.
While the total peak-to-valley height variation over distances of hundreds of microns or more is comparable to that of mechanically finished stainless steel, the topography of the profiles illustrates that the electropolished surface is much smoother over length scales on the order of one to ten micron. There is also evidence of small features systematically protruding from the electropolished surface – these may be individual grains from within the stainless steel.
CONTACT ANGLE MEASUREMENTS
There was no statistically significant difference in the contact angle between borosilicate silicate glass and soda-lime after heat treatment; Aluminosilicate glass had a statistically lower contact angle than soda-lime glass (p = 0.01); the difference between aluminosilicate and borosilicate glass was of marginal significance (p = 0.07). Mean contact angles measured from are other consistent experimental work on the heat treatment of glass.13.
FRICTION EXPERIMENTATION
- Glass Composition Effects
- Effects of Thermal Treatment
- Impact of Roughness and Humidity on Friction
- Wear and its Effects
- DISCUSSION
Statistical comparison of the coefficient of friction in several wet glass compositions for glass-to-glass friction. Mean and confidence intervals for coefficient of friction as a function of glass composition and humidity. Statistical comparison of the coefficient of friction between multiple wet glass compositions for glass-on-steel friction.
Means and confidence intervals for the coefficient of friction as a function of sequence order for the glass-to-glass and glass-to-steel friction test. Coefficient of friction for aluminosilicate glass on steel as a function of glass roughness, humidity and steel surface finish. Average coefficient of friction versus distance for glass-to-glass friction when comparing coated and smooth glass samples.
Average coefficient of friction versus distance for glass-on-steel friction as a function of relative humidity.
THERMAL TREATMENT
This elevated temperature creates a different local environment at the glass/steel interface, resulting in a relative humidity below that of the surrounding environment, limiting the resorption of surface moisture after thermal treatment. Given that all glass-steel combinations exhibited significantly increased friction at low humidity, it is likely that these samples had lower levels of adsorbed water on the glass surface prior to complete cooling and thus exhibited elevated friction coefficients such as those that would be associated with lower humidity.
GLASS COMPOSITION
Soda-lime glass showed a lower coefficient of friction than the other glass compositions against stainless steel. The lower hardness and greater susceptibility of soda-lime glass to water attack via stress corrosion mechanisms are both consistent with the lower average coefficient of friction of soda-lime glass over a wide humidity range.
ROUGHNESS, HUMIDITY, AND WEAR EFFECTS
SUMMARY AND CONCLUSIONS
Friction coefficient measurements taken under dry conditions yielded higher average friction coefficients than those performed in ambient humidity. This effect was more pronounced for the smooth-to-quiet interactions and is likely attributable to the reduced availability of water to participate in chemical bond breaking at the glass surface, as well as the ductile expansion of asperities increasing the effective area. of contact. The polished smooth tests consistently exhibited an increase in coefficient of friction with increasing moisture, while the smooth-to-rough or rough-to-rough combinations exhibited neutral or decreasing friction with increasing moisture.
This effect can be attributed to the relative thickness of the adsorbed water layers on the glass and stainless steel surfaces compared to the roughness of those surfaces affecting the effective contact area of the water films between these two surfaces and the resulting surface tension affects the creation of adhesive force. This is because these samples experienced the greatest friction of the experimental conditions due to the lack of water to help break the chemical bonds on the glass surface.
FUTURE WORK
Alternatively, one could exploit another aspect of this experiment as a means of investigating friction in other ways, depending on the purpose of the study. There are also simple ways to make a much more precise and controllable setup for the humidification apparatus used in this experiment: pass dry air through a known length of water-permeable tubing, and couple this with a temperature-controlled water source to modulate the steam-water pressure. Given the nature of the interactions observed in this work, the impact of variation in the mechanical properties of stainless steel on both the measured coefficient friction and the extent and nature of wear during the friction event would be an interesting area to examine.
Soda-lime or aluminosilicate glasses can be chemically strengthened, which has the dual effect of changing the chemical composition at the surface by replacing sodium with potassium, as well as changing the mechanical properties of the glass via the strengthened, compressive layer near the glass surface. Indeed, it is likely that the results would be materially different, since friction after long test duration has changed the surface conditions of the test specimens to such an extent.
Coefficient of Friction and Damage to the Contact Area During the Early Stages of Rubbing I: Glass, Copper, or Steel Against Copper,” Technical Note 3011, National Advisory Committee for Aeronautics, Lewis Flight Propulsion Laboratory, Cleveland, OH, September 1953. Correlation of Surface Quality and Wear of abrasive grain in optical glass lapping,” Tribol. Available at
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