Engineering topics

Fusaro, R. L.

Publications and source records attributed to Fusaro, R. L..

At least 37 records · Page 2

NASA NTRS1982

Polyimides: Tribological properties and their use as lubricants

Friction, wear, and wear mechanisms of several different polyimide films, solid bodies, composites, and bonded solid lubricant films are compared and discussed. In addition, the effect of such parameters as temperatures, type of atmosphere, contact stress, and specimen configuration are investigated. A friction and wear transition occurs in some polyimides at elevated temperatures and this transition is related to molecular relaxations that occur in polyimides. Friction and wear data from an accelerated test (pin-on-disk) are compared to similar data from an end use test device (plain spherical bearing), and to other polymers investigated in a similar geometry.

Fusaro, R. L.↗

NASA NTRS1982

Fundamental aspects of polyimide dry film and composite lubrication: A review

The tribological properties of polyimide dry films and composites are reviewed. Friction coefficients, wear rates, transfer film characteristics, wear surface morphology, and possible wear mechanisms of several different polyimide films, polyimide-bonded solid lubricants, polyimide solid bodies, and polyimide composites are discussed. Such parameters as temperature, type of atmosphere, load, contact stress, and specimen configuration are investigated. Data from an accelerated test device (Pin-on-Disk) are compared to similar data obtained from an end use application test device (plain spherical bearing).

Fusaro, R. L.↗

NASA NTRS1981

Tribological properties and thermal stability of various types of polyimide films

Thermal exposure experiments at 315 and 350 C were conducted on seven different types of polyimide films to determine which was the most thermally stable and adherent. The polyimides were ranked according to the rate of which they lost weight and how well they adhered to the metallic substrate. Friction and wear experiments were conducted at 25 C (room temperature) on films bonded to 440C HT stainless steel. Friction, film wear rates, wear mechanisms, and transfer films of the seven films were investigated and compared. The polyimides were found to fall into two groups as far as friction and wear properties were concerned. Group I had lower friction but an order of magnitude higher film wear rate than did group II. The wear mechanism was predominately adhesive, but the size of the wear particles was larger for group I polyimides.

Fusaro, R. L.↗

NASA NTRS1981

Effect of substrate surface finish on the lubrication and failure mechanisms of molybdenum disulfide films

An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrate was rough, flat plateaus were created during 'run-in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic-colored MoS2 films to a black, powdery material that was found by X-ray diffraction to consist primarily of alpha-iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha-iron and some residual MoS2. No molybdenum oxides were found.

Fusaro, R. L.↗

NASA NTRS1981

Tribological properties and thermal stability of various types of polyimide films

Thermal exposure experiments at 315 and 350 C were conducted on seven different types of polyimide films to determine which was the most thermally stable and adherent. The polyimides were ranked according to the rate at which they lost weight and how well they adhere to the metallic substrate. Friction and wear experiments were conducted at 25 C (room temperature) on films bonded to 440C HT stainless steel. Friction, film wear rates, wear mechanisms, and transfer films of the seven films were investigated and compared. The polyimides were found to fall into two groups as far as friction and wear properties were concerned. Group one had lower friction but an order of magnitude higher film wear rate than did group two. The wear mechanism was predominately adhesive, but the size of the wear particles were larger for group one polyimides.

Fusaro, R. L.↗

NASA NTRS1981

Effect of load, area of contact, and contact stress on the tribological properties of polyimide bonded graphite fluoride films

A pin-on-disk type of friction and wear apparatus was used to study the effect of load, contact stress and rider area of contact on the friction and wear properties of polyimide-bonded graphite fluoride films. Different rider area contacts were obtained by initially generating flats (with areas of 0.0035, 0.0071, 0.0145, and 0.0240 cm) on 0.476-cm radius hemispherically-tipped riders. Different projected contact stresses were obtained by applying loads of 2.5-to 58.8-N to the flats. Two film wear mechanisms were observed. The first was found to be a linear function of contact stress and was independent of rider area of contact. The second was found to increase exponentially as the stress increased. The second also appeared to be a function of rider contact area. Wear equations for each mechanism were empirically derived from the experimental data. In general, friction coefficients increased with increasing rider contact area and with sliding duration. This was related to the build-up of thick rider transfer films.

Fusaro, R. L.↗

NASA NTRS1980

Mechanisms of lubrication and wear of a bonded solid-lubricant film

The tribological properties of polyimide-bonded graphite fluoride films were investigated. A pin-on-disk type of testing apparatus was used; in addition to sliding a hemispherically tipped rider, a rider with a 0.95-mm-diameter flat area was slid against the film so that a lower, less variable contact stress could be achieved. Two stages of lubrication occurred: in the first, the film supported the load and the lubricating mechanism consisted of the shear of a thin surface layer between the rider and the bulk of the film. The second occurred after the bonded film had worn to the substrate, and consisted of the shear of very thin lubricant films between the rider and flat plateaus generated on the metallic substrate asperities. The film wear mechanism was strongly dependent on contact stress.

Fusaro, R. L.↗

NASA NTRS1980

Comparison of the weight loss and adherence of nine different polyimide films thermally aged at 315 C and 350 C in air

Thermal exposure experiments at 315 and 350 C were performed in air on nine different types of polyimides applied to thin 304 stainless steel foils. The tests were conducted to determine which polyimide was the most thermally stable and adherent when subjected to long exposure times at elevated temperatures. One polyimide designated PIC-7 was found to be more thermally stable than the others; however, it did not possess the adherent properties of PIC-2 and PIC-5. It was concluded that as far as thermal stability and adherence are concerned, five of the polyimides are more suitable for high temperature applications than the other four.

Fusaro, R. L.↗

NASA NTRS1980

Comparison of the tribological properties at 25 C of seven different polyimide films bonded to 301 stainless steel

A pin-on-disk type of friction and wear apparatus was used to study the tribological properties of seven different polyimide films bonded to AISI 301 stainless steel disks at 25 C. It was found that the substrate material was extremely influential in determining the lubricating ability of the polyimide films. All seven films spalled in less than 1000 cycles of sliding. This was believed to be caused by poor adherence to the 301 stainless steel or the inability of the films to withstand the high localized tensile stresses imparted by the deformation of the soft substrate under sliding conditions. The friction coefficients obtained for six of the polyimides varied between 0.21 to 0.32 while one varied between 0.32 to 0.39.

Fusaro, R. L.↗

NASA NTRS1980

Mechanisms of lubrication and wear of a bonded solid lubricant film

To obtain a better understanding of how bonded solid lubricant films lubricate and wear (in general), the tribological properties of polyimide-bonded graphite fluoride films were studied (in specific). A pin-on-disk type of testing apparatus was used; but in addition to sliding a hemispherically tipped rider, a rider with a 0.95 mm diameter flat area was slid against the film. This was done so that a lower, less variable contact stress could be achieved. Two stages of lubrication occurred. In the first, the film supported the load. The lubricating mechanism consisted of the shear of a thin surface layer (of the film) between the rider and the bulk of the film. The second occurred after the bonded film had worn to the substrate, and consisted of the shear of very thin lubricant films between the rider and flat plateaus generated on the metallic substrate asperities. The film wear mechanism was strongly dependent on contact stress.

Fusaro, R. L.↗

NASA NTRS1980

Lubrication and wear mechanisms of polyimide-bonded graphite fluoride films subjected to low contact stress

The tribological properties of polyimide-bonded graphite fluoride films were studied with a pin-on-disk friction apparatus. A 440 C HT stainless steel rider with a 0.95 millimeter diameter flat area was slid against the film in order to achieve a light, closely controlled contact stress. A 1 kilogram load was applied to this flat to give a projected contact stress of 14 megapascals. Two stages of lubrication were operating. In the first stage, the film supported the load and the lubricating mechanism appeared to be the shear of a thin surface layer of the film between the rider and the bulk of the film. The second stage began after the original film was worn away, and the lubricating mechanism appeared to be the shear of very thin lubricant layers between the flat area on the rider and flat plateaus generated on the sandblasted asperities of the metallic substrate. The major difference between the lubricating mechanisms of the hemispherical and flat riders was that the flat wore through the film much more slowly than did the hemisphere.

Fusaro, R. L.↗

NASA NTRS1980

Effect of Substrate Surface Finish on the Lubrication and Failure Mechanisms of Molybdenum Disulfide Films

An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrates were rough, flat plateaus were created during 'run in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X ray diffraction to consist primarily of alpha iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha iron and some residual MoS2. No molybdenum oxides were found.

Fusaro, R. L.↗

NASA NTRS1980

Effect of load, area of contact, and contact stress on the wear mechanisms of a bonded solid lubricant film

A pin on disk type of friction and wear apparatus was used to study the effect of load, contact stress and rider area of contact on the friction and wear properties of polyimide bonded graphite fluoride films. Different rider area contacts were obtained by initially generating flats (with areas of 0.0035, 0.0071, 0.0145, and 0.0240 cm) on 0.476-cm radius hemispherically tipped riders. Different projected contact stresses were obtained by applying loads of 2.5- to 58.8-N to the flats. Two film wear mechanisms were observed. The first was found to be a linear function of contact stress and was independent of rider area of contact. The second was found to increase exponentially as the stress increased. The second also appeared to be a function of rider contact area. Wear equations for each mechanism were empirically derived from the experimental data. In general, friction coefficients increased with increasing rider contact area and with sliding duration. This was related to the build up of thick rider transfer films.

Fusaro, R. L.↗

NASA NTRS1979

Lubricating and wear mechanisms for a hemisphere sliding on polyimide-bonded graphite fluoride film

Friction, wear life, rider wear, and film wear for a 440 C high-temperature-stainless-steel, hemispherically tipped rider sliding against polyimide-bonded graphite fluoride films were evaluated in a moist-air atmosphere at 25 C. Optical microscope and surface profilometry observations were made at various sliding intervals to determine how film thickness affected the lubricating and failure mechanisms of the films. Two lubrication regimes operated for the same load. In the first, the film supported the load and the lubricating mechanism consisted of the shear (plastic flow) of a thin layer of the lubricant between the metallic rider and the film surface. In the second, the film did not support the load (it was worn away) and the lubricating mechanism consisted of the shear of very thin lubricant films between flat areas generated on the rider and on sandblasted metallic asperities in the film wear track. Lubricant was supplied from the valleys between the asperities or from the sides of the wear track. With thicker films, wear life increased since a greater lubricant supply was available from the sides of the wear track.

Fusaro, R. L.↗

NASA NTRS1979

Mechanisms of graphite fluoride /CFx/n lubrication

Friction, wear and wear life results were compared with optical microscope observations as a function of sliding distance for graphite fluoride rubbed films applied to three surface finishes - polished, sanded and sandblasted. The lubricating process consisted of the plastic flow of thin films of graphite fluoride between flat areas on the rider and on the metallic substrate. If the substrate was rough, flat areas were created during run-in, and the graphite fluoride (CFx)n flowed across them. Wear life was enhanced by restricting radial (or transverse) flow of the graphite fluoride from the contact region by increasing surface roughness. Valleys in the roughened substrate surface served as a reservoir for graphite fluoride and as a deposit site for wear debris. Failure resulted from the gradual depletion of graphite fluoride from the contact region with the subsequent formation of powdery metallic debris that covered both rider and disk surfaces

Fusaro, R. L.↗

NASA NTRS1979

Effect of thermal aging on the tribological properties of polyimide films and polyimide-bonded graphite fluoride films

The effect of thermal aging on the weight loss, adherence, friction and wear of polyimide films and polyimide-bonded graphite fluoride films applied to 440C-HT stainless steel disks and to 304 stainless steel thin foils was studied. The films were exposed at temperatures of 315, 345, 370 or 400 C for 100 hours or more and then evaluated at temperatures of 25, 315 or 345 C in atmospheres of dry or moist air. Polyimide films were found to be brittle after thermal exposure; but polyimide-bonded graphite fluoride films possessed good adherence and gave low friction and wear results. Thus, polyimide-bonded graphite fluoride films appear to be good candidates for solid lubrication applications where long thermal soaks are prevalent.

Fusaro, R. L.↗

NASA NTRS1979

Effect of thermal aging on the tribological properties of polyimide films and polyimide-bonded graphite fluoride films

Weight loss, adherence, friction and wear of polyimide films and polyimide-bonded graphite fluoride films applied to stainless steel disks and to 304 stainless steel thin foils were studied. The films were exposed at temperatures of 315 D, 345 D, 370 D, or 400 C for 100 hours or more and then evaluated at temperatures of 25 D, 315 D, or 345 C in atmospheres of dry or moist air. Polyimide films were found to be brittle after thermal exposure; but polyimide-bonded graphite fluoride possessed good adherence and gave low friction and wear results. Polyimide-bonded graphite fluoride films appear to be good candidates for solid lubrication applications where long thermal soaks are prevalent.

Fusaro, R. L.↗

NASA NTRS1978

Lubrication and failure mechanisms of molybdenum disulfide films. 1: Effect of atmosphere

Friction, wear, and wear lives of rubbed molybdenum disulfide (MoS2 films applied to sanded 440C HT steel surfaces were evaluated in moist air, dry air, and dry argon. Optical microscope observations were made as a function of sliding distance to determine the effect of moisture and oxygen on the lubricating and failure mechanisms of MoS2 films. In general, the lubrication process consisted of the formation of a thin, metallic colored, coalesced film of MoS2 that flowed between the surfaces in relative motion. In air, failure was due to the transformation of the metallic colored, coalesced films to a black, powdery material. Water in the air appeared to accelerate the transformation rate. In argon, no transformation of MoS2 was observed with the microscope, but cracking and spalling of the coalesced film occurred and resulted in the gradual depletion of the film.

Fusaro, R. L.↗