Sliding friction and wear behaviour of vinylester and its composites under dry and water lubricated sliding conditions

In this paper, we studied and explored the tribological performance of pure vinylester (V), glass fiber reinforced (GFR), SiC filled glass fiber reinforced vinylester composite under dry and water lubricated sliding conditions. Friction and wear tests were carried out with configuration of a pin on a rotating disc under ambient conditions. Tests were conducted at normal load 10, 30 and 50 N and under sliding speed of 1.6 m/s, 2.8 m/s and 4 m/s. The results showed that the coefficient of friction decreases with the increase in applied normal load values both under dry and water lubricated conditions. On the other hand for pure vinylester specific wear rate increases with increase in applied normal load under dry sliding condition and decreases with increase in applied normal load under water lubricated conditions. However the specific wear rate for GFR vinylester composite and SiC filled GFR vinylester composite decreases with the increase in applied normal load both under dry and water lubricated conditions. Moreover, for the range of load and speeds used in this investigation the coefficient of friction and specific wear rates using water lubricant registered lower values than that of the dry condition. The specific wear rates for pure vinylester and vinylester + 50 wt.% GFR and SiC filled GFR vinylester composite under dry and water lubricated sliding condition were in the order of 10⁻⁷ mm³ N⁻¹ mm⁻¹.     

Friction and wear behavior of carbon nanotubes reinforced polyamide 6 composites under dry sliding and water lubricated condition

The friction and wear behavior of carbon nanotube reinforced polyamide 6 (PA6/CNT) composites under dry sliding and water lubricated condition was comparatively investigated using a pin-on-disc wear tester at different normal loads. The morphologies of the worn surfaces and counterfaces of the composites were also observed with scanning electron microscopy (SEM). The results showed that CNTs could improve the wear resistance and reduce the friction coefficient of PA6 considerably under both sliding conditions, due to the effective reinforcing and self-lubricating effects of CNTs on the PA6 matrix. The composites exhibited lower friction coefficient and higher wear rate under water lubricated condition than under dry sliding. Although the cooling and boundary lubrication effect of the water contributed to reduce the friction coefficient of the composites, the adsorbed water lowered the strength of the composites and also inhibited the formation of transfer layers on the counterfaces resulting in less wear resistance. With the increasing normal loads, the friction coefficient of the composites increased under the dry sliding and decreased under the water lubricated condition, owing to inconsistent influences of shear strength and real contact areas. The specific wear rate of the composites increased under both sliding conditions.     

Effects of potassium titanate whiskers and carbon fibers on the wear behavior of polyetheretherketone composite under water lubricated condition

The tribological behaviors of polyetheretherketone (PEEK) composite reinforced by carbon fiber (CF) and potassium titanate whiskers (PTW) have been investigated using the pin-on-disk configuration at different applied loads under water lubricated condition. The effects of micrometer carbon fiber and sub-micrometer PTW on the wear properties of the hybrid composite have been discussed. It was found that the PEEK/PTW/CF composite showed excellent tribological performance in water condition. High wear resistance and low friction coefficient were achieved under a wide range of loads. It was revealed that the two fillers worked synergetically to enhance the wear resistance of the hybrid reinforced PEEK composite. The carbon fiber carried the main load between the contact surfaces and protected the matrix from further severe abrasion of the counterpart. At the same time, the exposed PTW out of the polymer matrix around the fiber inhibited the direct scraping between the fiber edge and counterpart tip in some degree, so that the fibers could be less directly impacted during the subsequent sliding process and they were protected from severe damage. In addition, the reinforcement effect of PTW on PEEK could reduce the stress concentration on the carbon fiber-matrix interface, and thereby reduce the CF failure/damage. The reinforcement effect of PTW on PEEK might also restrict the crack initiation and propagation on the surface and subsurface of the composite, and therefore to protect the matrix from fatigue failure during the sliding process.     

Friction and wear behavior of three-dimensional braided carbon fiber/epoxy composites under lubricated sliding conditions

The friction and wear characteristics of three-dimensional (3D) braided carbon fiber-epoxy (C_3D/EP) composites under lubricated sliding conditions against a quenched medium-carbon steel counterface were studied. Wear tests were performed under different loads at two velocities. Comparative wear tests under dry conditions were carried out to investigate the influence of lubrication. Tribological properties of the C_3D/EP composites with various fiber loadings and two different fiber-matrix adhesion strengths were assessed. It was found that the lubricated contact promoted lower wear rates and friction coefficients. Compared to dry sliding, the tribological performance of the C_3D/EP composites under lubrication was less dependent on fiber content, fiber-matrix bonding, load, and velocity than dry sliding. The worn surfaces of the C_3D/EP composites were analyzed by scanning electron microscopy (SEM) to explore the relevant mechanisms.     

Syntactic foam core metal matrix sandwich composite under bending conditions

The present work aims at characterizing a metal matrix syntactic foam core sandwich composite under three-point bending conditions. The sandwich comprises alumina hollow particle reinforced A356 alloy syntactic foam with carbon fabric skins. Crack initiation in the tensile side of the specimen causing failure of the skin, followed by rapid failure of the core in the direction applied load, is observed as the failure mechanism. Crack propagation through the alumina particles is observed in the failed specimens instead of interfacial failure. The average maximum strength, flexural strain and stiffness were measured as 91.2 ± 5.6 MPa, 0.49 ± 0.06% and 20.6 ± 0.7 GPa respectively. The collapse load is theoretically predicted using mechanics of sandwich beams. Experimental values show good agreement with theoretical predictions.     

Long term high temperature oxidation resistance of a nanoceria coated 316 SS under dry air conditions

In this work, nanoceria dip coated and uncoated 316 stainless steels were exposed to dry air at 1073–1273 K for times of up to 250 h. From this work, measured activation energies, Q = 256 kJ mol⁻¹ and Q = 240 kJ mol⁻¹ were found for coated and uncoated 316 SS, respectively. In the coated steel, the activation energy for oxidation cannot be attributed to a single mass transport mechanism. In addition, the scale morphologies, as well as the dominant oxide phases were determined by X-ray diffraction means. It was found that in the nanoceria dip coated steels, the scale was fine grained and highly adherent. Oxidation at increasing temperatures in the coated steels favored the development of the spinel ((Mn, Cr)₃O₄ structure and at 1273 K with the presence of Fe₂O₃ was severely hindered. In contrast, in the uncoated steel, a relatively thick scale, predominantly Fe₂O₃ developed and it exhibited severe damage through spallation and detachment from the steel substrate. Also, the resultant grain structure was rather coarse and it consisted of faceted grains with continuous nucleation/growth at grain ledges.     

Strength of a weld-seam metal and glass-enamel coating composite under conditions of cyclical creep

In the temperature interval 293–573 K we have experimentally established the relationship of the failure stress of a coating (UES 300 with a base sublayer of brand 3132) in a weld-seam metal (Sv08GA steel) composite with a glass-enamel coating under conditions of cyclical creep at levels of up to t_test=6.10⁵ sec. It was noted that below 448 K the failure stress of the coating over the metal of the weld seam is lower by 50–60 MN/m² than in a composite with a base layer of a hot-rolled thick-sheeted 08GT-brand steel exhibiting greater ductility in tests of short duration, but under identical temperature conditions. The derived results are explained by the appearance within the weld-seam metal in contact with the coating of additional local stresses generated by volumetric changes within the process of residual austenite decay.Translated from Problemy Prochnosti, No. 8, pp. 58–61, August, 1991.     

Wear characteristics of plasma-nitrided CrMo steel under mixed and boundary lubricated conditions

An investigation of the sliding wear mechanisms of a plasma-nitrided CrMo steel is undertaken using a running-in procedure that eliminates severe wear under mixed and boundary lubricated conditions. In the running-in procedure, using a pin-on-disc wear machine, smooth contact surfaces are obtained rather than the rough contact surfaces generally found in laboratory experiments. This enables the wear mechanisms to be investigated more clearly, particularly mild wear processes. The work shows no measurable nor visible wear under full fluid film lubricated conditions, the existence of polishing under mixed lubricated conditions and micro-pits under boundary lubricated conditions. The results presented in this paper indicate that a mild abrasive wear mechanism predominates under mixed lubricated conditions and a micro-fatigue wear mechanism under boundary lubricated conditions. Examination of the microstructure reveals the formation of white layer regimes on the contact surfaces after tests under boundary lubricated conditions, which suggests severe work-hardening of the contact surfaces. This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of roughness parameters on coefficient of friction under lubricated conditions

Surface texture and thus roughness parameters influence coefficient of friction during sliding. In the present investigation, four kinds of surface textures with varying roughness were attained on the steel plate surfaces. The surface textures of the steel plates were characterized in terms of roughness parameter using optical profilometer. Then the pins made of various materials, such as Al-4Mg alloy, Al-8Mg alloy, Cu, Pb, Al, Mg, Zn and Sn were slid against the prepared steel plates using an inclined pin-on-plate sliding tester under lubricated conditions. It was observed that the surface roughness parameter, namely, R _a , for different textured surfaces was comparable to one another although they were prepared by different machining techniques. It was also observed that for a given kind of surface texture the coefficient of friction did not vary with R _a . However, the coefficient of friction changes considerably with surface textures for similar R _a values for all the materials investigated. Thus, attempts were made to study other surface roughness parameters of the steel plates and correlate them with coefficient of friction. It was observed that among the surface roughness parameters, the mean slope of the profile, Del a(Δ _a ), was found to explain the variations best.     

不同测试条件下TiN薄膜的摩擦学特性研究

采用电弧离子镀技术在45#钢衬底表面沉积了TiN薄膜.用显微硬度计测试了薄膜的硬度,用球一盘式摩擦磨损试验机评价了在不同测试条件下(干摩擦,水润滑,油润滑)TiN薄膜的摩擦学性能,用表面轮廓仪测试了磨痕处的磨痕轮廓,用配有能谱仪(EDS)的扫描电镜(SEM)观察和测试了磨痕形貌和磨痕处主要化学元素组成.结果表明,相对于干摩擦,水润滑和油润滑条件下,TiN薄膜的摩擦系数和磨痕深度都有明显降低的趋势.干摩擦条件下,薄膜表现为磨粒磨损和氧化磨损;水润滑条件下,薄膜表现为疲劳磨损,水对薄膜起到边界润滑作用;油润滑条件下,薄膜几乎无磨损,油起到流体润滑作用.     

Structural behavior of double-lap shear adhesive joints with metal substrates under humid conditions

Structural adhesive bonding is very often used joining method in aerospace and automotive industry, but in civil engineering, especially in façade applications, semi-flexible or semi-rigid adhesives are still rarely used. The article is focused on experimental analyses of structural adhesive joints intended for façade applications (e.g. bonding of façade cladding elements to the supporting substructure). The experimental study contains a comparison of the structural behavior of two different adhesives in joints with aluminum or zinc-electroplated steel substrates with various surface pre-treatments. The main goal of the study is a comparison of the mechanical properties of joints exposed and unexposed to laboratory ageing conditions; immersion on demineralized water according to ETAG 002 (Guideline for European Technical Approval for Structural Sealant Glazing Kits). Water content in adhesive layer can change significantly its mechanical properties and adhesion of glue to the substrate. Ageing resistance of joint can be improved by durability increasing of the substrate. For this reason, two different substrate materials with various surface treatments (mechanical roughening, smooth surface, anodizing) were tested. Different adhesive resistance against humid conditions was observed depending on the substrate material and pre-treatment. STP polymer joints showed strength reduction by 30% after immersion for almost all substrates, while acrylate adhesive proved 20% strength reduction for roughened aluminum substrate and 60% strength reduction for zinc-electroplated steel substrate with a roughened surface. The zinc-electroplated steel substrate showed problematic adhesion in case of the acrylate adhesive both reference set of specimens and specimens exposed to laboratory ageing. The positive effect of roughening on adhesion and ageing resistance was clearly observed in the specimens bonded by the acrylate adhesive.

     

Dynamic behavior of berea sandstone for dry and water-saturated conditions

Wave profile measurements have been performed on dry and water-saturated Berea sandstone under shock compression loading conditions using a single-stage light gasgun. The wave motion was monitored with a VISAR velocity interferometer. The impact velocities achieved in the experiment were in the range between 433 m/s and 1013 m/s. Significant differences were observed in the dynamic response of dry and water-saturated Berea sandstone. This work presents the experimental results as well as simulation results obtained using a phenomenological model of Berea sandstone. The model includes effects of compaction, plastic yielding and damage. In the model, the behavior of the water-saturated material was addressed with a modified effective stress model. The simulated wave profiles agree with the experimental data for both dry and water-saturated conditions. This validates the current model and provides a baseline for its further application.     

Nanotribological investigation of magnetic rigid disks lubricated with perfluoropolyether lubricant under varying conditions

This paper studies the nanotribological behavior of magnetic rigid disks dip-coated with ultra thin perfluoropolyether (PFPE) Z-Dol 4000 lubricant layers up to 4 nm thick prior to or after exposure to ultraviolet (UV) light irradiation. Lube bonding ratios (LBRs) of 43-91% were achieved by varying the UV irradiation time. The nanotribological and mechanical properties of the disks were measured with a nanotribometer under varying loading conditions. The effect of the LBR on the nanotribological behavior of the disks was also elucidated. We found that the lubricated disks after UV treatment performed better compared to the lubricated disks without UV treatment. The experimental results indicated that the LBR of about 50% could achieve the best contact-start-stop and flyability performances.     

Failure behavior of coated nickel-based superalloy under thermomechanical fatigue

Thermomechanical fatigue (TMF) is a major life limiting factor for gas turbine blades. In this study, the failure behavior of NiCrAlY overlay coated nickel-based superalloy M963 was investigated under out of phase (OP) TMF. All tests were carried out under mechanical strain control with a cyclic period of 200 s. Results revealed that the fatigue life of high velocity oxygen fuel spraying (HVOF) coated specimen was longer than that of air plasma spraying (APS) coated one, but shorter than that of bare superalloy M963 at a given strain range. It was found that cracking process in the APS coating was different from that in the HVOF coating, which was shown by the sketches to understand the crack initiation and propagation behavior.     

纳米层包覆TiO2粒子复合乳胶涂料的光催化和耐老化性能研究

采用氯化法、通过表面无机包覆制得了主要物相为金红石型TiO2的光催化剂纳米粉体,在乳胶涂料中的应用表明,复合了该产品的乳胶涂料具有优良的光催化杀菌和净化空气的性能,以及优异的耐老化性.提出削弱基体材料耐老化性的不是TiO2的光催化作用,而是TiO2晶格缺陷引起的光化学活性.     

Tribological investigations of polyetherimide composite

Polyetherimide (PEI), commercially known as ULTEM and manufactured by GEC (USA), is one of the newest high-performance thermoplastics. Its graphite and short-glass-fibre (GF) filled composition was evaluated for friction and wear properties. Tribological studies of the material sliding against mild steel, under different loads, counterface roughnesses and sliding distances were performed on a pin and disc configuration. It was observed that this composite displayed very good wear resistance due to glass-fibre reinforcement and low friction due to the solid lubricant graphite. The wear mechanism was studied with scanning electron microscopy by observing the worn pin and disc surfaces. Fatigue was observed to be the main factor in wear, along with adhesive and abrasive modes.     

Tribological investigation of diamond-like carbon coated micro-dimpled surface under bovine serum and osteoarthritis oriented synovial fluid

Osteoarthritis-oriented synovial fluid (OASF), i.e., that typical of a patient with osteoarthritis, has different physical and biological characteristics than bovine serum (BS), a lubricant widely used in biotribological investigations. Micro-dimpled and diamond-like carbon- (DLC) coated surfaces are key emerging interfaces for orthopedic implants. In this study, tribological performances of dimpled surfaces, with and without DLC coating, have been investigated under both BS and OASF. The friction tests were performed utilizing a pin on a disk tribometer, whereas contact pressure, speed, and temperature were simulated to a ‘medium walking gait’ of hip joint conditions. The mechanical properties of the specimen and the physical properties of the lubricant were characterized before the friction test. Raman analysis was conducted to identify the coating condition both before and after the test. The DLC-coated dimpled surface showed maximum hardness and residual stress. A DLC-coated dimpled surface under an OASF lubricated condition yielded a lower friction coefficient and wear compared to those of plain and dimpled specimens. The higher graphitization of coated materials with increasing load was confirmed by Raman spectroscopy.     

Tribological behaviour and acoustic emissions of alumina, silicon nitride and SAE52100 under dry sliding

The friction, wear and acoustic emission behaviour of various combinations of alumina, silicon nitride, and SAE52100 steel, operating under dry sliding conditions, was investigated. A designed ball-on-flat-disc type of tribometer was used to conduct these experiments. This apparatus, equipped with a force sensor, using silicon strain gauges, measured simultaneously the normal load and friction force. Both forces were used to determine the real-time value of the dynamic coefficient of friction. The AE signal arising from the interaction of the surfaces in dynamic contact was also detected and a data acquisition system was used to gather this signal as well as the outputs from the force sensor, at high frequency. The effects of test duration, sliding speed and normal load on the above mentioned tribological parameters were evaluated. The interest of this study further extended to assess the correlations that may exist between the integrated rms acoustic signal (AE) and the friction mechanisms, wear volume, friction work as well as the material removal power. Under the specific conditions of the present experiments, no consistent relation was found between the variations of AE and corresponding dynamic coefficient of friction (COF) as function of time. The variation of COF and wear rate, obtained considering a fixed total sliding distance of 500 m, as function of a range of sliding speed (0.05–2.5 m/s) and normal load (5–40 N) are presented. It was found that the test duration has an important impact on wear results of the experiments conducted at different sliding speeds and fixed travelling distance. More expected behaviour was observed when the relationships between the AE and wear volume, friction work, and material removal power were investigated considering the data obtained at different loadings and fixed sliding speed. Some models representing interesting relationships which could be used for predicting tribological properties in the case of practical applications, similar to the tribo-systems investigated in this study, are proposed.