Decrease In Friction Research Articles

Fabrication of MXene@Fe3O4@PNA composite with photothermal effect as water-based lubricant additive

Improving the tribological performance of water via designing nanomaterials as lubricant additive has garnered mounting interest. In this work, the poly-(N-isopropylacrylamide) microgel is grafted onto Fe3O4 nanoparticles surface (Fe3O4@PNA) via free radical polymerization. Then, the Fe3O4@PNA can self-anchored on the MXene nanosheets via hydrogen bonding interaction to obtain MXene@Fe3O4@PNA composite. The as-prepared MXene@Fe3O4@PNA can effectively reduce friction and wear when used as a water-based lubricant additive. Compared with pure water, the average coefficient of friction (COF) and wear volume decrease by 61% and 78.7%, respectively. The lubrication mechanism was analyzed by focused ion beam technique-TEM (FIB-TEM) and X-ray photoelectron spectroscopy (XPS). The outstanding tribological performance of MXene@Fe3O4@PNA is attributed to the synergistic lubrication effect of MXene and Fe3O4@PNA. Interlayer shear of MXene and spherical Fe3O4@PNA can make MXene@Fe3O4@PNA play a full role of sliding friction and rolling friction mechanism, which can induce tribo-chemical reactions to form a protective film on the contact area of the friction pair. In addition, the hydrophilic groups of the MXene@Fe3O4@PNA can adsorb a large number of water molecules and form a hydration layer, reducing the agglomeration of nanosheets and acting as a boundary lubrication film. Moreover, the as-prepared MXene@Fe3O4@PNA exhibit excellent photothermal conversion performance in both underwater environment and dry state. Based on this characteristic, infrared light can be collected efficiently and stored quickly. Then, convert and utilize it. Therefore, the multifunctional MXene@Fe3O4@PNA has a broad application prospect as a water-based intelligent lubrication additive.

Lubricity effectiveness of bio-lubricant modified with multi-wall carbon nanotube and organic polymer

The development of effective bio lubricants with anti-friction and wear properties is gaining recognition due to their ecofriendly nature and good lubrications in mitigating challenges associated with friction and wear on tribo-components during lubrication. In this research, rapeseed oil served as the base lubricant, and the high frequency reciprocating rig was utilized to examine the responsiveness of the multiwall carbon nanotubes (MWCNTs) and Eichhornia crassipes carboxylmethyl cellulose (EC-CMC) polymer additives. To determine the constituents and strength of the formulations, the samples were characterized using scanning electron microscope, Energy-dispersive X-ray, Fourier transform infrared spectroscopy, Raman, and X-ray photoelectron spectroscopy. The tribological test was conducted in terms of synergistic tendency, load carrying capacity, friction and wear reduction as well as tribo-film nature. The investigation came to the following conclusions: Depending on the operating conditions, all nanoparticle suspensions showed decreases in friction and wear relative to the base oil; MWCNTs yielded better wear reduction performance while EC-CMC demonstrated outstanding friction reduction operations compared to based lubricant; the suspensions with 0.8% MWCNTs +0.5% EC-CMC had the best tribological behavior, exhibiting high percentage reduction on friction (67.8%) and wear (37.9%) with low levels on the surface roughness. Using XPS analysis, the detection of additive elements and tribo-films on the wear surfaces was validated, and their nature was analyzed in the context of the related tribo-chemistry findings. The study concluded that effective friction reduction during testing is a result of the additive's rapid penetration into the interface region and its nanosized structure.

Force-Based Characterization of the Wetting Properties of LDPE Surfaces Treated with CF4 and H2 Plasmas.

Low-density polyethylene (LDPE) films are widely used in packaging, insulation and many other commodity applications due to their excellent mechanical and chemical properties. However, the water-wetting and water-repellant properties of these films are insufficient for certain applications. In this study, bare LDPE and textured LDPE (T-LDPE) films were subjected to low-pressure plasmas, such as carbon tetrafluoride (CF4) and hydrogen (H2), to see the effect of plasma treatment on the wetting properties of LDPE films. In addition, the surface of the LDPE film was textured to improve the hydrophobicity through the lotus effect. The LDPE and T-LDPE films had contact angle (θ) values of 98.6° ± 0.6 and 143.6° ± 1.0, respectively. After CF4 plasma treatments, the θ values of the surfaces increased for both surfaces, albeit within the standard deviation for the T-LDPE film. On the other hand, the contact angle values after H2 plasma treatment decreased for both surfaces. The surface energy measurements supported the changes in the contact angle values: exposure to H2 plasma decreased the contact angle, while exposure to CF4 plasma increased the contact angle. Kinetic friction force measurements of water drops on LDPE and T-LDPE films showed a decrease in friction after the CF4 plasma treatment, consistent with the contact angle and surface energy measurements. Notably, the kinetic friction force measurements proved to be more sensitive compared to the contact angle measurements in differentiating the wetting properties of the T-LDPE versus 3× CF4-plasma-treated LDPE films. Based on Atomic Force Microscopy (AFM) images of the flat LDPE samples, the 3× CF4 plasma treatment did not significantly change the surface morphology or roughness. However, in the case of the T-LDPE samples, Scanning Electron Microscopy (SEM) images showed noticeable morphological changes, which were more significant at sharp edges of the surface structures.

Thermal case study and generated vortices by dipole magnetic field in hybridized nanofluid flowing: Alternating direction implicit solution

A vortex is a location in a fluid where the flow revolves around an axis line, which may be flat or curved. Researchers must look at vortices whenever and wherever they are found since they are present in natural systems. The purpose of this investigation is to present an understanding of how the nanofluid flow (driven by an external mechanism) interacts with the magnetic field produced by a nearby paced magnetic source. While most of the scientific literature is enriched with investigations dealing with the problems assuming a uniform magnetic field occupying the flow field, the current analysis is devoted to studying the complex interaction of the spatially varying magneto force with the nanofluid flow. We have noticed that the magnetic field has caused the evolution of new vortices (which are very important while analyzing any flow model due to their importance in interpreting fluid mixing and mass transport phenomena) in the flow field, thus adding much more significance to our work. The single-phase model (SPM) has been used to describe the hybrid nanofluid whereas the numerical solution to the governing differential equations has been obtained by employing an algorithm based on the central difference discretization and the alternating direction implicit method. The governing factors for the current examination are the Reynolds number, the magneto variable, and the volumetric concentration of the nanoparticles, with the ranges, considered being 1≤Re≤150, 0≤Mn≤150 and 0≤ϕ≤0.2, respectively. The analysis reveals that the Nusselt number (Nu) steepens noticeably at the enclosure's upper left corner. 20% increment in nanoparticle volume fraction may result in up to 72% boost in the Nusselt quantity whilst causing an up to 33% decrease in skin friction. Furthermore, compared to copper, iron oxide nanoparticles are shown to be more dependent on drag force. The flow field is dominated by two almost similar main vortices while there is no magnetic source, but as the magnetic source gets stronger, the bottom vortex gets stronger. It enlarges and constricts the top vortex, breaking it down while creating two new, weaker vortices. As it produces three vortices at comparatively lower values of the pertinent parameters, the Reynolds number functions as a catalyst for the action of the magneto force variable. Finally, the Nusselt quantity and frictional factor both significantly alter once the nanostructure is incorporated into the base fluid.

Drag reduction by means of an array of staggered circular cavities at moderate Reynolds numbers

Further insight into the physics of boundary layers developing over an array of circular cavities at moderate Reynolds numbers (Reθ up to 3400) is gained from hot wire boundary layer surveys on a range of parameters. The findings are consistent with literature as to the possibility of reducing skin friction drag with circular perforations. The results evidence a modification of the mean velocity profile, an increase of the wake parameter and the shape factor associated to a decrease of the skin friction. The modifications of the boundary layer as well as the skin friction reduction are more pronounced when the open area ratio is increased, which is achieved by increasing the cavity diameter or equivalently by decreasing the inter-cavity spacing. The turbulent activity is shifted in the upward direction, the burst intensity decreases in the buffer layer (10<Y+<35) and increases in the upper part of the logarithmic region/beginning of outer layer (80<Y+<200) with the formation of an outer peak in the turbulence intensity profile. The premultiplied spectra and the streamwise shear stress profiles evidence an energy surplus in the same part of the boundary layer and for the highest open area ratios a “bi-hump” behaviour. The formation of outer quasi-streamwise rollers is believed to be the cause of this energy hump in the spectrum. The turbulence statistics show a striking similarity with the turbulent boundary layer in presence of wall-normal blowing. It is believed that the cavities promote a vertical velocity component that displaces the turbulent activity towards the outer region. Different hypotheses to explain the modification of the flow statistics are detailed in the paper.

The Influence of Temperature on Anisotropic Wettability Revealed by Friction Force Measurement.

Anisotropic surfaces with special wettability under various temperatures are of both fundamental interest and practical importance in many fields. However, little attention has been paid to the surfaces at temperatures between room temperature and the boiling point of water, which is partially due to the lack of a suitable characterization technique. Here, using the MPCP (monitoring of the position of the capillary's projection) technique, the influence of the temperature on the friction of a water droplet on the graphene-PDMS (GP) micropillar array (GP-MA) is investigated. The friction forces in the orthogonal directions and the anisotropy in the friction decrease when the GP-MA surface is heated up, based on the photothermal effect of graphene. The friction forces also decrease along the pre-stretching direction but increase in the orthogonal direction when the stretching is increased. The change in the contact area, the Marangoni flow inside a droplet, and the mass reduction are responsible for the temperature dependence. The findings strengthen our fundamental understanding of the dynamics of drop friction at high temperatures and could pave the way for the design of new functional surfaces with special wettabilities.

Design model of radial bearing with bearing sleeve elastic bearing profile and metal coated shaft surface

The article is devoted to the development and analysis of a design model of lubricant movement in the working gap of a radial journal bearing with an elastic bearing profile of the bearing sleeve surface and a metal coating of the shaft surface with truly viscous properties. New mathematical models have been developed based on basic equations that take into account the flow of a truly viscous liquid for a “thin layer”, the malleability of the bearing sleeve support surface - the Lame equation, compressibility - the equation of state, the Weisbach - Darcy formula, the profile of the molten contour of the metal coating of the shaft surface - the rate of dissipation of mechanical energy. The results of the numerical analysis of the refined models obtained by changing the design of the radial bearing, as well as taking into account the compressibility of the lubricant and the coating melt, allowed us to obtain an effectiveness qualitative assessment of the malleable bearing profile of the bearing sleeve and the shaft with a metal coating. A comparative analysis of the obtained results of theoretical and experimental studies of radial bearing structures: with and without metal coating; elastic support profile; without taking into account the elasticity of the support profile; taking into account compressibility; without taking into account the compressibility of the lubricant. At the end of the research complex, experimental tests were carried out that confirmed the correctness of the results of theoretical studies. The ingenuity of the developed design models, taking into account the use of additional lubrication with a metal coating on the shaft surface to compensate for an emergency shortage of lubricant, the compressibility of the lubricant, as well as the malleability of the bearing surface, consists in the application of a technique for obtaining their exact self-similar solutions. As a result of theoretical, experimental research and comparative analysis of the available scientific results with the obtained ones, it was found that the use of the studied radial journal bearings, taking into account the above factors, significantly increases the bearing capacity (8-9 %), and the coefficient of friction decreases by 7…8 %.

Influence of water content on elastohydrodynamic friction and film thickness of water-containing polyalkylene glycols

Lubricants with a functional water portion have demonstrated a drastic reduction in friction under elastohydrodynamic lubrication conditions. With water-containing polyalkylene glycols, superlubricity with coefficients of friction &amp;lt;0.01 have been measured in model and gear contacts. In addition to the low friction, their calorimetric properties make them particularly interesting for application in electrified vehicles because the liquid can simultaneously serve as lubricant for the gearbox and coolant for the electric motors and the power electronics. In this study, the influence of water content between 8 wt% and 40 wt% of water-soluble polyalkylene glycols on friction and film thickness in elastohydrodynamically lubricated rolling-sliding contacts such as in gears and bearings is investigated. A polyalphaolefine oil is used as a reference. Friction has been measured on a ball-on-disk tribometer and film thickness on an optical tribometer. For a water content of 40 wt%, superlubricity with coefficients of friction down to 0.004 are found. The decrease in friction is up to 95% compared to the polyalphaolefine reference. The measured film thickness decreases with increasing water content. For a water content of 8 wt%, the film thickness is similar to that of the polyalphaolefine reference while at the same time friction is still reduced by 81%. Depending on the friction and film thickness requirements of a specific tribosystem, the water content of a water-containing polyalkylene glycol can be chosen accordingly.

Predictive Analytics and Ship-Then-Shop Subscription

This paper studies an emerging subscription model called ship-then-shop. Leveraging its predictive analytics and artificial intelligence (AI) capability, the ship-then-shop firm curates and ships a product to the consumer, after which the consumer shops (i.e., evaluates product fit and makes a purchase decision). The consumer first pays the up-front ship-then-shop subscription fee prior to observing product fit and then pays the product price afterward if the consumer decides to purchase. We investigate how the firm balances the subscription fee and product price to maximize its profit when consumers can showroom. A key finding is the ship-then-shop firm’s nonmonotonic surplus extraction strategy with respect to its prediction capability. As prediction capability increases, the firm first switches from ex ante to ex post surplus extraction (by lowering fees and raising prices). However, if the prediction capability increases further, the firm reverts to ex ante surplus extraction (by raising fees and capping prices). We also find that the ship-then-shop model is most profitable when (i) the prediction capability is advanced, (ii) the search friction in the market is large, or (iii) the product match potential is large. Finally, we show that the marginal return of AI capability on the firm’s profit decreases in search friction but increases in product match potential. Taken together, we provide managerially relevant insights to help guide the implementation of the innovative subscription model. This paper was accepted by Dmitri Kuksov, marketing. Supplemental Material: The online appendix is available at https://doi.org/10.1287/mnsc.2023.4723 .

Reactive formation of a few 2D layers of MoS2 using triboactive Mo surfaces and their interaction with anti-wear additives and dispersants

In this work, we study the use of triboactive surfaces containing metallic Mo for promoting the in-situ formation of MoS2 in the presence of lubricants containing S. We evidence the in-situ formation of (002)-oriented MoS2 layers that lead to a decrease in friction from 0.3 down to 0.07. High-resolution transmission electron microscopy analyses reveal that the macroscopic reduction in friction is caused by only a few self-assembled 2D-MoS2 monolayers that are formed via a tribochemical reaction between the metallic Mo from the surface and the S from the lubricant. In the absence of S in the lubricant, friction is high and unsteady.We also address the interaction of the in-situ tribochemically formed MoS2 layers with lubricant co-additives, such as anti-wear and dispersants. The reactive in-situ formation of MoS2 using Mo triboactive surfaces can occur in conjunction with the formation of 60 nm thickness Zinc dialkyl dithiophosphate (ZDDP) tribofilms, as revealed by transmission electron microscopy. In contrast to that, the use of dispersants prevents the formation MoS2 and results in a high coefficient of friction.The results obtained contribute to the development of greener lubrication concepts for reducing friction and wear, as they rely on triboactive surfaces for the formation of MoS2 and avoid the use of noxious organo-molybdenum compounds in lubricants.

Microstructure evolution and vacuum tribological properties of surface nitriding layer on a TiZrAlV alloy fabricated by laser nitriding

The evolution mechanisms of phase, microstructure and vacuum tribological properties for Ti–20Zr-6.5Al–4V under different laser beam diameters have been investigated by using laser surface nitriding (LSN). Results indicate that all the LSN samples are mainly composed of α phase and Ti(Zr)N phase, besides, Ti(Zr)N0.3 phase can also be obtained, which is based on a change in the ratio of liquefied nTi(Zr)/nN. With the laser beam diameter decreasing from 3 to 1 mm, the thickness and density of nitride layer increase significantly, which contribute to the increased energy input density. EPMA results indicate that the nitrides mainly exist in the form of Ti(Zr)xNy, and the distribution transformation of Al and V elements has also been analyzed. As the laser beam diameter decreases, the coefficient of friction decreases, and the sample with 1 mm laser beam diameter display the lowest coefficient of friction (∼0.333). Also, the wear volume and wear rate of the LSN sample with 1 mm laser beam diameter are the smallest, which are both reduced by about 40% compared with the original sample. After analysis, the wear pattern of the LSN samples can be confirmed as the composite of adhesive wear and abrasive wear. Nitride dendrites can form a support skeleton between the wear surface and friction pair, which can significantly reduce the wear of LSN sample surface. The results of this work prove the feasibility of improving the surface wear resistance of Ti–20Zr-6.5Al–4V by LSN.

Influence of sintering temperature on mechanical and tribological characteristics of copper based composite reinforced by 2D hybrid material

The effect of sintering temperature on the mechanical and tribological characteristics of 2D phase reinforced copper-based composite has been investigated in the present study. The Cu-based composites containing 2 wt. % of(GO + MoS2)NP were sintered at different temperatures (1023, 1073, 1123, and 1173 K) by microwave sintering process. The microstructural features observed by SEM and HRTEM of composites suggest that as the sintering temperature increases (GO + MoS2)NP pocket formation tendency also increases, which also governs the mechanical and tribological characteristics of composites. As the sintering temperature elevated, the ultimate tensile strength of the composite decreases, whereas friction and wear rate decrease with increase in temperature up to 1123 and beyond 1123 increase in friction and wear has been observed. The decrease in strength with increasing sintering temperature has been attributed to the grain size increment and increase in (GO + MoS2)NP pocket size at the grain boundaries. However, the decrease in friction and wear rate has been ascribed to the ease of extrusion of (GO + MoS2)NP from the pockets for the composites sintered at high temperature, rather than extrusion of (GO + MoS2)NP of fillers from the intra-grainular sites, i.e., for the composites sintered at lower temperature.

Evaluation of mechanical and tribological behavior of galvanized, galvalume and polyurethane-coated steel sheets

The current study is performed on three coated steel sheets to evaluate their mechanical and tribological properties. The optical micrograph reveals the dark pearlite structure in the ferrite matrix, whereas the grain size analysis reveals the 4.07 μm mean grain size of the ferrite. The scratch hardness test reveals better scratch-resistant properties for all three experimental samples. The Nanoscratch test reveals a decrease in friction with increasing load from 50 mN to 150 mN for the colour-coated samples. The tensile study shows higher YS and UTS values (410 MPa and 450 MPa, respectively) for the galvalume sample, followed by galvanized and colour-coated steel. In contrast, a higher ductility (~33%) is observed for the colour-coated sample, followed by galvanized and galvalume samples. It is evident and appropriate from the dry heat resistance test that all three steel sheets, viz. galvalume, galvanised and colour coated sheet, can withstand 120 °C of heat for 24 h. So, all the samples show improved heat resistance properties. Taber abrasion resistance test results reveal that the colour-coated sample shows improved abrasion resistance due to the polyurethane coating followed by galvalume and galvanized steel samples.

In situ Growth and Characterization of Lubricious Carbon-Based Films Using Colloidal Probe Microscopy

Silicon oxide-doped hydrogenated amorphous carbon (a-C:H:Si:O) is an important form of diamond-like carbon (DLC) for tribological applications, primarily because of its enhanced thermal stability and reduced dependence of friction on environmental humidity. As with other DLCs, its mechanisms of lubrication are still an active area of research, though it is now known that surface passivation and tribofilm growth are important factors. In this study, tribofilm formation for a-C:H:Si:O is examined at the microscale by using steel colloid atomic force microscopy probes as the sliding counterface. This approach provides some inherent advantages over macroscale tribology experiments, namely that the tribofilm thickness and stiffness can be tracked in situ and correlated directly with the friction response. The results of these experiments show that the tribofilm grows rapidly on the steel colloid following a period of counterface wear and high friction. The friction drops more than 80% upon nucleation of the tribofilm, which is attributed to a decrease of more than 80% in adhesion combined with a decrease in the estimated interfacial shear strength of at least 65%. Approximately 80% of the friction decrease occurs before the tribofilm reaches a thickness of 2 nm, suggesting that only the near-surface properties of the tribofilm provide the needed functionality for its effective lubrication mechanisms.

Influence of Manufacturing Tolerances on the Behavior of Pneumatic Seals using EHL Simulations

The sealing friction in pneumatic spool valves is influenced by several factors, like the lubricant and sealing material properties, the topography of the contacting surfaces and the geometry. In practice, surface roughness and geometry are subject to manufacturing tolerances. This publication presents a simulative investigation on how these tolerances affect the sealing contact. For that, friction force and leakage are calculated for different bore diameters and surface roughness. An increase in bore diameter leads to an almost linear decrease in friction and an increase in expected leakage. Higher surface roughness amplitudes are predicted to increase both friction and expected leakage.

Sedimentary facies characterization through CPTU profiles: An effective tool for subsurface investigation of modern alluvial and coastal plains

ABSTRACTCone penetration tests, a method that is typically used to determine the engineering properties of soils, can be used as an effective tool for refined subsurface stratigraphic investigations of alluvial and coastal plains, aside from the geographic location. High‐resolution calibration of piezocone penetration tests (CPTU) with 20 sediment cores enabled the detailed characterization of alluvial, deltaic and coastal depositional systems of the Po Plain. Twelve cored facies associations, typical of alluvial and coastal plain environments, were characterized based on four distinct CPTU profiles: basic cone resistance (Qc), sleeve friction (Fs), water pore pressure (U) and friction ratio (FR). Sandy facies associations (fluvial/distributary channel, bay‐head delta, transgressive barrier, delta‐front/beach‐ridge) typically have high (&gt;4 MPa) Qc, low‐to‐negative U and low (&lt;2%) FR. Muddy deposits (well‐drained/poorly‐drained floodplain, swamp, lagoon and prodelta) exhibit opposite trends. Heterolithic facies associations (crevasse‐levée, offshore/delta‐front transition) display characteristic seesaw profiles. Plotting of late Quaternary deposits onto the latest version of the cone penetration test typical soil behaviour chart (Robertson, 2010) enables the identification of distinctive facies associations reflecting distinctive grain size. CPTU interpretation leads to sedimentary facies recognition well beyond the simple lithological differentiation and, in particular, allows the refined characterization of clay‐rich and silt‐rich depositional units (swamp clays and peats, central‐inner and outer lagoon, proximal/distal prodelta deposits) that exhibit only subtle differences in lithology. CPTU data can also serve for the accurate detection of key stratigraphic surfaces with potential engineering applications, such as the Pleistocene–Holocene boundary. This latter, a common feature of several alluvial and coastal plain successions, is commonly marked by an abrupt upward decrease of basic cone resistance and sleeve friction from Late Pleistocene, pedogenized, stiff strata to overlying Holocene, organic‐rich, soft deposits. This study offers an updated CPTU‐facies characterization method that could be suitable for subsurface investigations of modern alluvial and coastal plains worldwide.

Mechanical and tribological properties of 5A06 aluminum alloy at low temperature

There are significant differences in the mechanical and tribological properties of 5A06 aluminum alloys subjected to a wide temperature range, and the related research has received very limited attention so far. In this paper, the mechanical properties of 5A06 aluminum alloy were obtained by tensile test at temperature as low as 77K, which laid a foundation for analyzing its tribological properties. Then, dry linear reciprocating sliding wear tests were performed on a ball-on-disc tribometer to explore the friction behavior and wear mechanism of 5A06 aluminum alloy at different temperatures from low temperature (173K) to room temperature (293K). Finally, the wear morphology and chemical composition of the worn surface were characterized by an optical 3D measurement system and a scanning electron microscope equipped with an energy dispersive spectroscopy. The results indicate that the ambient temperature affects the tribological properties of 5A06 aluminum alloy by changing its mechanical properties and the dissipation of friction heat. Compared with 293K, the coefficient of friction decreases by 14.66% and the wear rate decreases by 70.79% at 173K. The main wear mechanisms of 5A06 aluminum alloy are delamination wear and oxidation wear at 293K and 273K, and a combination of abrasive wear, adhesive wear and oxidation wear at 223K and 173K.

Investigation of cryogenic friction and wear properties of Invar 36 alloy against Si3N4 ceramic balls

The existing materials for liquefied natural gas (LNG) cryogenic submersible pump bearings are very susceptible to wear and failure in LNG environments where oil lubricants and greases are ineffective, posing a major hazard to the safety of LNG storage and transportation. Therefore, searching for a type of material with excellent cryogenic tribological properties for improving the life of LNG bearings has become a huge challenge for researchers. Invar 36 alloy, as a low expansion nickel-titanium alloy, is used in control instruments, moulds, laser control equipment, and materials of LNG transport hull at temperatures below −162 °C. However, there is a lack of research data in the field of bearings. Currently, the Si3N4 ceramic balls are widely used in ceramic hybrid ball bearings and exhibit excellent tribological properties. In this work, the tribological performance of Invar 36 alloy is mainly investigated against Si3N4 ceramic ball under extremely cryogenic and dry conditions using the modified ball-on-disk tribometer with a cryogenic module, with temperatures as low as −196 °C. All experiments are performed at loads of 0.5 N, 1 N, 1.5 N, and 2 N, and at temperatures of 20 °C, 0 °C, −78 °C, and −196 °C, respectively. The experimental results show that the coefficient of friction (COF) and wear rate decrease with temperature and load, with a minimum value of −196 °C. The Invar 36 alloy exhibits excellent tribological properties, whose COF decreases gradually from 20 °C to −78 °C. However, as the temperature drops to −196 °C, the COF decreases abruptly, reaching a minimum value at −196 °C. On the contrary, the COF gradually increases with load. In addition, a commercial bearing grade material (G95Cr18 steel) is tested and compared under the same conditions, proving that Invar 36 alloy exhibits better tribological properties than G95Cr18 steel, with a wear rate 55.43% lower than G95Cr18 steel at −196 °C. Further simulation comparisons demonstrate that, due to its extremely low coefficient of thermal expansion, Invar 36 alloy exhibits higher toughness and strength than G95Cr18 steel under cryogenic conditions. This study complements the tribological data of Invar 36 alloy and G95Cr18 steel against Si3N4 ceramic balls under different temperatures and loads and provides important theoretical guidance and technical support for the bearings’ future development of LNG cryogenic submersible pump.

Experimental Studies on Some Clays Leading to Instability

The landslide problem in the city of Constantine (Algeria) is mostly due to clayey soil, which is covering the whole area. Therefore, all the structures and foundations built over such soil are quite vulnerable. The sensitivity of this soil increases during the rainfall season, which might reach an extreme magnitude and cause damage to the structures. To understand some aspects of the failure of the mentioned soil and its mechanism, a large campaign of geotechnical characterization was undertaken using samples from the area. The specific gravity, Atterberg limits, and coefficient of lateral earth pressure at rest were determined. Samples were tested in triaxial stress path cells over a range of stresses, with the test being either stress- or strain-controlled, leading to sliding phenomena under different stress levels. The clays can be classified as over-consolidated soils. The test program and the characterization study indicated that Kois directly related to the stress history of the soil and also dependent upon the state of the sample before the test (i.e., undisturbed or disturbed). The clay minerals in the Mio-Pliocene landslide zones in Constantine are mostly montmorillonite and kaolinite, which have the lowest frictional resistance. As the montmorillonite content increases, the angle of internal friction decreases. The present study focuses on the critical state analysis since all the behavior problems of these tested samples show a peak shear strength, which is characteristic of over-consolidation materials that could lead to instability in this area. Doi: 10.28991/CEJ-2023-09-02-012 Full Text: PDF

Synthesis and Micro hardness Studies of Polymer Nanocomposites of ZnS with PVK

The synthesis and microhardness studies of ZnS with PVK ((Poly N-Vinylcarbazole) nanocomposites are presented. The thin films was form with different loding of ZnS in PVK using chemical rout method and characterized them SEM (Scanning Electron microscope), XRD (X-ray diffraction), AFM (Atomic Force Microscope) and study their mechanical properties. XRD shows ZnS have cubic nanocrystals structure, with particle size about 3 to 12 nm. Broadening of line shows the formation of amorphous compound. The SEM, AFM images reveal clustering of particles within 10 to 100 nm. These three studies reveal the particle size respectively increases with ZnS loading in the PVK. The microhardness study on pure PVK and ZnS with PVK nanocomposites helps us to understand the modification in properties due to inter- and intra- molecular interactions. It is seen that ZnS with PVK nanocomposites exhibit lower value of microhardness as compare to pure PVK and minimum for highest loading (50% ZnS) of ZnS in PVK. For each ZnS loading at first, the microhardness increases with the load and after that, beyond particular load, it obtain a saturated value, so it can be say the samples are fully strain-hardened at this load. The micro hardness also corresponds to frictional force. With increasing load the coefficient of friction decreases and the frictional force increases linearly with the increasing load. Therefore, the change in Vickers hardness number (Hv) is curvilinear with load.