EFFECT OF HUMIDITY ON TRIBOLOGICAL PROPERTIES OF SELECTED FRICTION JUNCTIONS WITH AN EVALUATION OF ACOUSTIC EMISSION

The study aimed to compare the effect of humidity on the operation of tribological systems. The tested friction and wear are external properties; therefore, their values may differ significantly depending on the operating parameters of the friction junction and environmental conditions. Tribological tests were carried out on a TRB3 tribometer in a dry sliding mode at a relative humidity of 50% ± 5% and 90% ± 5% in the ball-on-disc configuration with a load of 15 N. The friction junction consisted of a sample made of 100Cr6 steel, and three counter-samples were made of 100Cr6, SiC, and Al2O3 steel. The geometric structure of the surface was examined with an optical profiler. The tribological test results showed reduced linear wear and friction coefficient at a relative humidity of 90% ± 5% compare to its 50% ± 5%. The paper also presents the results for the sound recorded in the 16-bit linear PCM standard and analysed in a Spectra-Plus program.

Influence of the taper on the fretting wear of the femoral stem-femoral head taper junction in total hip prosthesis

Purpose The purpose of this paper is to study the roughness effect on the fixation of taper junction components and surfaces wear in terms of taper surface design. The roughness of the femoral heads’ taper and of the femoral stems’ trunnions can influence the fretting wear of the taper junction. Design/methodology/approach It was analysed whether a microgrooved taper surface of the femoral stem trunnion improves the fixation and reduces the wear rate at the taper junction of the hip prosthesis. Two models have studied: a femoral head with a smooth tapered surface combined with a microgrooved stem trunnion and a femoral head with a smooth tapered surface combined with a trunnion that had a smooth surface of the tapered. To compare the wear evolution between these two models, a computerised finite element model of the wear was used. Findings The results obtained after analysis carried out during millions of loading cycles showed that the depth of the linear wear and the total material loss were higher for the femoral heads joined with microgrooved trunnions. The main conclusion of this paper is that the smooth surfaces of the taper and of the trunnions will ensure a better fixation at the taper junction, and therefore, will reduce the volumetric wear rates. Originality/value A higher fixation of the taper junction will reduce the total hip prosthesis failure and, finally, it will improve the quality and durability of modular hip prostheses.

Load dependent microstructural evolution in an as-cast 26% Cr high chromium cast iron during unlubricated sliding

In the current study, an as-cast 26% Cr high chromium cast iron (HCCI) alloy was subjected to dry-sliding linear wear tests, under different loads. The loads were selected based on analytically computing the critical load (PC) i.e., the load necessary to induce plastic deformation. The PC was calculated to be 15 N and accordingly, a sub-critical load (5 N) and an over-critical load (20 N) were chosen. The influence of increasing the load during the wear test was investigated in terms of the matrix microstructural behaviour and its ability to support the surrounding carbides. The morphological aspects of the wear tracks, and the deformed matrix microstructure adjacent and underneath the track was analysed by confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM), respectively. No evidence of plastic deformation of the matrix was observed below PC. On the contrary, at loads equal to and higher than PC, the austenitic matrix plastically deformed as evidenced by the presence of slip bands. Electron backscattered diffraction (EBSD) measurements in terms of grain reference orientation deviation, and micro-Vickers hardness of the austenitic matrix indicated a deformation depth of about 40 µm at the maximum applied load of 20 N. The active wear mechanisms during sliding were a combination of both adhesive and abrasive wear, although increasing the load shifted the dominant mechanism towards abrasion. This was primarily attributable to the increased propensity for carbide cracking and fracturing, combined with the inability of the hardened austenitic matrix surface and sub-surface to adequately support the broken carbide fragments. Moreover, the shift in the dominant wear mechanism was also reflected in the wear volume and subsequently, the wear rate.

An Experimental Study of the Wear Characteristics of Tubulars Made from Corrosion-Resistant Alloys

Summary Casing wear is the process of progressive loss of wall thickness owing to relative motion between the drillstring and casing. The amount of casing wear depends on conditions, such as the downhole forces, the accumulated time of contact between drillstring and casing, and the materials used. This process is complex and involves abrasive, adhesive, and corrosive wear mechanisms that are difficult to predict. To deal with the complexity of the conditions, a simple but effective wear model is used in the industry to estimate tubular wear in drilling and intervention operations. The model is based on abrasive and adhesive wear, and the effects of corrosion are not considered. In addition, an empirical part of the model known as the correction factor is based exclusively on experimental carbon-steel test data. Tubulars made of corrosion-resistant alloys (CRAs) are known to exhibit abnormal wear characteristics. A series of experiments has been designed and performed to investigate the wear characteristics of CRAs. These experiments resulted in excessive wear factors for the CRA casing samples, demonstrating their susceptibility to wear. This study finds that omitting the correction factor from the calculation procedure can greatly improve wear estimates for some CRAs. Removing the correction factor results in a linear wear-work relationship that reflects the actual wear trends from test results. However, further studies are needed to confirm correction factors and more accurate wear calculation procedures for CRA tubulars in general.

SOME COMMENTS ON THE INTERPRETATION OF THE TRIBOLOGICAL WEAR COEFFICIENT

An original model of tribological wear is presented, an alternative to the commonly used J.F. Archard’s model. The impossibility is established of a full conversion of mechanical work into the heat of dissipation and thereby of avoiding wear in the sliding friction of solids. The assumption is consequently questioned that only some contacts of surface asperities are subject to temporary wear. Material wastage is assumed to occur at each contact of asperities. The volume of worn material is dependent on the volumetric wear coefficient of the “energy dissipation zone” in friction. The dimensions of the zone are determined in both the elements in friction. Linear wear intensities and volumetric wear are described in analytical terms. The thermodynamic analysis of the tribological process indicates some limitations to these intensities. Energetic efficiencies of solid wear and heating as a result of friction are defined. Some new interpretations of the wear coefficient are proposed.

Investigation of Micromechanical Properties and Tribological Behavior of WE43 Magnesium Alloy after Deep Cryogenic Treatment Combined with Precipitation Hardening

This study investigated the micromechanical and tribological properties of WE43 alloy (Mg-Y-Nd-Zr) alloy subjected to cryogenic treatment and precipitation hardening. Microindentation tests were carried out in the range of load from 100 to 1000 mN. The introduction of deep cryogenic treatment (DCT) was shown to increase hardness and Young’s modulus, and reduce the total indentation work. As the load set during the tests increased, a gradual decrease in the measured values was observed, indicating a significant relationship between the indent size and the value of the measured parameters. Cryogenic treatment used in conjunction with precipitation hardening (after solutioning and after aging) reduces the tribological wear of the alloy. Tests have shown an almost twofold reduction in the area of the wear trace and in the volumetric wear of the alloy, as well as a more than twofold reduction in linear wear, with relatively small fluctuations in the coefficient of friction. Abrasion was the main mechanism of wear. Areas where microcutting, adhesion and plastic deformation occurred were also observed. The results indicate the significant effectiveness of the applied heat treatment in improving the service life of the WE43 alloy containing rare earth metals.

Enhancement of the Mechanical and Tribological Properties of Aluminum-Based Alloys Fabricated by SPS and Alloyed with Mo and Cr

Multicomponent aluminum-based alloys doped with chromium (Cr) and molybdenum (Mo), fabricated by spark plasma sintering (SPS), derived from a powder mixture prepared by mechanical alloying, were studied in this work. The morphology of the pristine and worn surfaces was analyzed using a scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system. The obtained alloys exhibited higher hardness (73 and 72) for the Al–Mo and Al–Cr alloys, respectively, compared to reference bronze. Besides improved hardness, SPS-sintered alloys also showed a lower value of the weight and linear wear and the highest score-resistance compared to bronze. The enhanced tribological behavior is related to the formation of secondary structures on the friction surfaces of rubbing pairs, which in turn reduce wear. For the first time, the present research has demonstrated the effectiveness of the addition of Mo and Cr for the fabrication of sintered multicomponent Al-based alloys with a tailored microstructure that induces the formation of secondary structures on the tribosurfaces due to the self-organization processes during friction.

Polymeric Composite Materials of Tribotechnical Purpose with a High Level of Physical, Mechanical and Thermal Properties

Polymeric composites (PC) of tribological applications with a high level of physical, mechanical and thermal properties based on aromatic polyamide and silica gel have been developed. Regularities have been obtained that describe the effect of the filler content in PC on the friction coefficient, temperature on the friction surface and the intensity of linear wear rate of the studied PC-steel friction pair. It was found that the optimal silica gel content in the polymer matrix is 10 wt %. The morphology of the steel surface of friction after friction interaction with PC based on aromatic polyamide and silica gel was studied. The formation of an antifriction film on the steel surface of friction was discovered, which contributes to a decrease in the friction coefficient, temperature on the friction surface, and the linear wear intensity of the studied PC. The influence of the load and sliding speed on the main tribotechnical characteristics of the PC-steel friction pair has been studied. Mathematical laws were derived that describe the influence of the main external factors (load and sliding speed) on the friction coefficient and intensity of linear wear rate of the studied friction pair. Physical, mechanical and thermal investigations of the developed PC were carried out and it was found that the introduction of 10 wt % silica gel contributes to their 5–10 % increase.

Experimental Study of Tool Wear when Milling Tropical Wood with Various Tool Materials

The paper presents a study on the performance of cutter tip for wood milling process. The tests were performed with the tropical wood samples which were milled in the double sided wood planer, the measured micro-geometrical parameters encompassing the linear wear and tooltip radius. The study primarily contributes to developing a far better understanding of the physical nature of cutting tool wear in response with the growing concern of many researchers. Given this basis, it does not only assist the selection of reasonable cutting tool but also enable the detection of the patterns in the cutting tool wear process. In terms of tool wear and bluntness, there has been a number of researches taking account into the physical nature of cutting tools, - providing basis for selection of cutting tools apart from clarification of the current pattern of tool wear and bluntness. The load applied to the cutter during wood milling is the load that changes marks periodically. When starting to work after tool sharpening and finishing, the first stage changes the microscopic geometry - tool run-in process (rapid initial wear), followed by constant conditions of wear before a rapid wear which leads to failure at last. The objective of this study is to determine the influence of the cutting path to the tooltip radius and linear wear of the cutting edge. The paper employs method of least squares and variance analysis in application of the Minitab software to determine regression equations for relation of the tooltip radius and linear wear to the relative cutting length. The ultimate goal is to predict the life of cutting tool when milling tropical wood.

Modelling of contact and tribotechnical parameters of metal–polymer gears taking into account wear and correction of teeth

The estimation and the analysis of the arising contact pressures and tribotechnical parameters, that is, wear and durability, of metal-polymer spur gears using the author's computational method are presented in this study. Gears with a steel gear and pinion made of polyamide PA6 modified with dispersed carbon fibers (CF) or glass fibers (GF) whose content was 30%, PA6 + 30CF and PA6 + 30GF correspondingly, are studied. This took into account the parity of engagement, the effect of composite pinion teeth wear and gear correction. Quantitative and qualitative regularities of change of the specified parameters depending on composite type and gear correction type are established. It is found that the teeth wear of composite toothed wheels has a significant effect on reducing the values of the initial maximum contact pressures in the engagement. The distribution of linear wear along the teeth working profile and the localization of its maximum values, depending on the correction of engagement, are determined. The minimum durability of metal–polymer gears is calculated by simplified and improved methods. The optimal values of the correction coefficients at which the minimum durability is highest for both combination types of metal–polymer gears with height and angular teeth correction are established. The durability of metal–polymer gears with a driving pinion made of PA6 + 30CF composite calculated with the improved method is about seven times higher than the pinion made of PA6 + 30GF composite. In contrast to the methods of calculation of metal gears known from publications, the method presented in this study takes into account such practically significant factors as change of radii of tooth profile curvature owing to wear, their correction and number of teeth pairs at the engagement. In metal–polymer gears, there are no analytical calculation methods for modelling wear and tribological durability compared with that of the author's method.