Unidirectional carbon fiber reinforced epoxy was tested in ambient air at three different levels of relative humidity and under full immersion in demineralized water. Reciprocating sliding tests were ...performed at 23 °C against either stainless steel or alumina balls moving in parallel or anti-parallel direction to the fibers. We demonstrate in this work that humidity and water immersion affect significantly the fiber debonding. Under sliding against stainless steel or alumina at low relative humidity, fiber debonding is more pronounced than at high relative humidity and at water immersion. The wear depth increases with increasing relative humidity when sliding against stainless steel, whereas it remains practically constant against alumina. For all test conditions, the wear depth is larger when tested against stainless steel than against alumina. It was found that the thin moisture film formed at the surface of the stainless steel counter body leads to a higher corrosive risk than water immersion. More precisely, we demonstrate that high humidity leads to the production of oxide debris originated from the stainless steel ball which increases markedly the wear by abrasion. These debris lead to a high fluctuation of the coefficient of friction measured on carbon fiber reinforced epoxy composite sliding against stainless steel at 85% RH, whereas a steady state coefficient of friction is noticed against alumina.
Intermetallic alloys such as titanium aluminides (TiAl) are potential materials for aerospace applications at elevated temperatures. TiAl intermetallics have low weight and improved efficiency under ...aggressive environments. However, there is limited information about wear behavior of these alloys and their microstructure. The present work aims to study the influence of the microstructure in the tribological behavior of TiAl intermetallic alloy (45Al-2Mn-2Nb(at%)-0.8 vol%TiB2). Wear tests were performed on samples manufactured by centrifugal casting (CC) and hot isostatic pressure (HIP). Reciprocating sliding wear test was carried out for TiAl, it was combined with different loads and frequencies. Wear tracks were analyzed through opto-digital microscopy and electron microscopy (SEM). The results obtained reveal that CC intermetallics present the lowest volume wear lost, approximately 20% less than HIP intermetallics. This good behavior could be related to the high hardness material, associated with the main microstructure where CC intermetallic has nearly lamellar microstructure and HIP intermetallics present duplex microstructure.
The effect of brake oil on sliding behavior of carbon/carbon (C/C) and carbon/carbon−silicon carbide (C/C−SiC) composites was investigated with the variation of laminate orientation and surface ...conformity. The partial and low conformity contacts with the normal and parallel orientations of laminates were considered. The normal load was varied from 50 to 90 N in a step of 10 N. The friction and wear behavior was investigated under reciprocating sliding conditions. The results showed that friction coefficient and wear loss of composites with normal orientation of laminates were larger as compared to those of composites with parallel orientation of laminates. C/C composites with normal orientation of laminates yielded the highest value of friction coefficient. Wear loss decreased by a maximum of 78%, and friction coefficient decreased by a maximum of 49% in low conformity contacts as compared to partial conformity contacts. The presence of brake oil reduced the adhesion tendency of compacted wear debris because the formation of friction film was difficult, and thus, friction behavior was affected. The wear debris retention between the contact surfaces due to confined area motion in reciprocating sliding depicted the tribological behavior.
In the field of tribology, many applications operate in the elastohydrodynamic lubrication (EHL) regime e.g., automotive engines, gears and rolling element bearings. In the EHL regime hydrodynamic ...performances are significantly enhanced by the contact bodies elastic deformations and the lubricant piezoviscosity. IssyOsborne is a procedure package for Igor Pro designed to be used by researchers in the field of tribology and fluid mechanics. It allows to easily calculate the film thickness distribution in lubricated sliding contact in EHL regime under time-varying conditions. This calculation is performed given the contact conditions, the fluid properties and the contact bodies properties. IssyOsborne can be used for deceleration, acceleration and reciprocating motions. In the algorithm, a full-analytical resolution of the Reynolds equation was derived. Validated experimentally, the analytical film thickness equations perfectly modeled the mechanisms behind film formation, such as squeeze due to the transient evolution of the film thickness over time, asymmetry and hysteresis in film distribution.
PTFE/α-alumina composites are well known to exhibit very low wear rates compared to unfilled PTFE and various other PTFE-matrix composites. The improved wear life of these composites is attributed in ...part to the formation of a uniform protective transfer film on the metal countersurface. It is postulated that the retention of transferred material and the recirculation of third bodies between the transfer film and running surface of the polymer composite are necessary for the maintenance of low wear within this tribological system. The accumulation of these third bodies was observed in reciprocating sliding tests on countersamples prescribed with aligned roughness. Wear performance of the polymer composite was tested as a function of the between the sliding direction and the aligned roughness of the countersample, ranging from parallel to perpendicular to the sliding direction. The wear rate of roughness oriented with the sliding direction was 300 times higher than roughness perpendicular to the sliding direction, revealing the importance of surface morphology and third body retention.
Friction and wear properties of WC–Co cemented carbides with Co concentrations ranging from 6 up to 12
wt% and WC grain sizes in the sub-micrometer scale have been examined in reciprocating sliding ...wear experiments using a high-frequency TE77 pin-on-plate system. The aim of the work was to investigate the influence of test parameters such as normal contact force, oscillating velocity and sliding distance on the tribological characteristics. The tests were carried out under unlubricated conditions. The generated wear was quantified volumetrically by means of surface topography scanning measurements. The changes in test parameters gave a variation in wear of more than one order of magnitude. A marked increase in wear was seen as the load increased, whereas the friction coefficient displayed an opposite trend. Raising the oscillating speed was found to increase both friction coefficient and wear level. The wear tracks and wear debris were analyzed by scanning electron microscopy (SEM), energy disperse X-ray spectrometry (EDX) and X-ray diffraction (XRD). The observed mechanisms of wear are discussed with respect to the magnitude of wear that was measured.
CrN coatings were deposited on 2024Al alloy using arc ion plating apparatus. The CrN coatings'topography was observed by using scanning electron microscopy (SEM). The composition and structure of CrN ...coatings were determined by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The reciprocating sliding friction and wear characteristics of CrN coatings against Si3N4 ceramic balls in water and air were investigated by using the ball-on-disk configuration with 1 mm amplitude (A). The influences of normal load (W) and reciprocating frequency (f) on the friction coefficients (mu) and the specific wear rate of CrN coatings were studied. The worn surfaces on CrN coatings were observed by SEM and analyzed by EDS. The results showed that there were many white particles and dimples on gray surface. The Cr and N concentrations for the white particles were higher than those of gray parts. With increases in the normal load and reciprocating frequency, the friction coefficient all decreased in air and water, while the CrN coatings'specific wear rate decreased with normal load, and slightly fluctuated with reciprocating frequency. The friction coefficient decreased linearly with frictional energy (muWfA), and the logarithmic values for the CrN coatings'specific wear rate increased linearly with friction coefficient (mu), while decreased linearly with frictional energy (muWfA). The microanalysis of the worn surface of CrN coatings indicated that the formation of tribofilms with the Cr-N-Si-Al-O was occurred during friction testing.
In order to reveal tribo-magnetization phenomenon of ferromagnetic materials, a new apparatus which involved reciprocating friction tests of pin-on-block type under the geomagnetic field has been ...built to perform the tests. Based on the changes of the surface magnetic field of wear scar and the macroscopic and SEM analyses, it is concluded that tribo-magnetization of ferromagnetic materials is a two-stage process and the demarcation point of these two stages is the transition point of the friction forms. Furthermore, the shape and the position of wear scar can be estimated through measuring the surface magnetic field of wear scar.
•A new reciprocating friction apparatus has been built to perform the tests.•Tribo-magnetization of pure iron materials was a two-stage process.•The size of wear scar can be estimated through measuring the magnetic field.•The initial magnetic field have great influence on tribo-magnetization.
Plastic recycling in the automotive industry is a priority. In this study, the effect of adding recycled polyvinyl butyral (rPVB) from automotive windshields on the coefficient of friction (CoF) and ...specific wear rate (
) of a glass-fiber reinforced polyamide (PAGF) is investigated. It was found that, at 15 and 20 wt.% of rPVB, it acts as a solid lubricant, reducing CoF and
up to 27% and 70%, respectively. Microscopical analysis of the wear tracks showed that rPVB spreads over the worn tracks, forming a lubricant layer, which protects the fibers from damage. However, at lower rPVB content, fiber damage cannot be prevented as the protective lubricant layer is not formed.
