Search Results (4,165)

Compressive strength and Young’s modulus are key design parameters in rock engineering, essential for understanding the mechanical behavior of carbonate rocks. Understanding the mechanical behavior of carbonate rocks under varying load conditions is crucial for geotechnical stability analysis. In this paper, empirical relationships are developed to predict the mechanical properties of carbonate rocks. A series of uniaxial and triaxial compression experiments were conducted on carbonate rocks including limestone, dolostone, and granite from Wyoming. In addition, experimental data on different carbonate rocks from the literature are compiled and integrated into this study to evaluate the goodness of fit of our proposed empirical relationships in the prediction of compressive strength and Young’s modulus of carbonate rocks. Regression analysis was used to develop predictive models for the uniaxial compressive strength (UCS), Young’s modulus (E), and triaxial compressive strength (${\sigma }_1$) incorporating parameters such as the porosity (n) and confining pressure (${\sigma }_3$). The results indicated that the UCS and Young’s modulus showed a power relationship with porosity (n), whereas the ${\sigma }_1$ showed a linear relationship with n and ${\sigma }_3$. Furthermore, an analytical model expanded from the wing crack model was applied to predict the ${\sigma }_1$ of limestone based on the coefficient of friction, the initial level of damage, the initial flaw size, and the fracture toughness of the rock. The model showed a good predictability of the ${\sigma }_1$ with a mean bias (i.e., the ratio of the measured to the predicted strength) of 1.07, indicating its reliability in accurately predicting the rock strength. This predictability is crucial for making informed engineering decisions, design optimization, and improving safety protocols in practical applications such as structural analysis and manufacturing processes. Full article

The aim of this research is to analyze the thermophysical, wettability, and tribological properties of some base oils of different nature (synthetic and mineral), as well as of formulated oils, to find potential transmission oils for electrical vehicles. Regarding the thermophysical properties, viscosity, density, and viscosity index were analyzed. Surface tension and contact angle were also measured to obtain the wettability performance of tested lubricants. The highest viscosities were found for the PAO8 oil and the lowest for the G-III 3 base oil, while the highest densities were found for the formulated oils. Concerning wettability performance, the surface tensions of PAOs and G-IIIs rise gradually with an increase in viscosity, the surface tension being the greatest for G-III 6 and the lowest for G-III 3. Finally, in the tribological characterization, the lowest coefficients of friction and produced wear were found with the formulated lubricants, due to the presence of an additive package. Full article

Asphalt pavement skid resistance, governed by surface texture, is critical for traffic safety. Most research has focused on full-depth textural characteristics, often overlooking the depth of tire–pavement contact under real traffic conditions. This study introduces the concept of the Effective Depth of Skid Resistance (EDSR) to describe the effective depth of tire–asphalt contact, improving skid resistance assessment accuracy. Using blue linear laser scanning, surface textures of three common asphalt pavements with wearing courses—AC-13, AC-16, and SMA-13—were analyzed, and friction coefficients were measured using a British pendulum. After pre-processing three-dimensional texture data, fractal dimensions at various depths were calculated using the box-counting method and correlated with the friction coefficients. Previous studies show an insignificant correlation between full-depth asphalt pavement textures and skid resistance. However, this study found a significant positive correlation between skid resistance and pavement textures at specific depths or the EDSR. A depth with a correlation exceeding 0.9 was defined as the EDSR. Linear formulas were established for each pavement type within these EDSR ranges. A theoretical model was developed for predicting skid resistance, showing an over 80% accuracy against real-world data, indicating its potential for improving road surface performance detection. Full article

Tantalum diffusion layers were fabricated on 316L stainless steel substrates using the double glow plasma surface alloying technology (DGPSAT). The optimization rules of the Fe-Ta diffusion layer under varying alloying times were investigated, focusing on the effects of processing parameters on the phase structure and microstructure. The results indicate that, as the alloying time increases, the surface wrinkled structure in the Fe-Ta alloy layer gradually transforms into a nanoscale acicular α-Ta structure, improving surface roughness and water contact angle. The surface microstructure influenced by the alloying time enhanced mechanical properties significantly, increasing Vickers hardness from 152 HV_0.2 to 970 HV_0.2, improving bonding strength, and reducing the friction coefficient to 0.5. Electrochemical testing showed that the corrosion rate of the tantalum diffusion layer was significantly reduced from 1.04 × 10⁻² mm/a to 2.83 × 10⁻⁴ mm/a, demonstrating the excellent corrosion resistance. The island growth pattern during the formation of alloy layers was simulated by molecular dynamics. Replacing bulk materials with tantalum diffusion layers can economize rare metals, reduce costs, and be of great significant for the special equipment applications in harsh environments. Full article

Ni-W-Al₂O₃ nanocomposite coatings were fabricated using ultrasonic-assisted jet electrodeposition (UAJED) to improve the wear resistance of agricultural machinery parts. To find the best combination of process parameters, the response surface plotter, contour plotter, and pre-set plotter in the JMP (version Pro 14.3.0) software were employed to investigate the effects of various process parameters (jet rate, Al₂O₃ content, and ultrasonic power) on the microhardness of the nanocomposite coatings. The surface morphology, microstructure, and properties of the coatings, which were prepared under various combinations of process parameters, were studied through scanning electron microscopy (SEM), an X-ray diffractometer (XRD), transmission electron microscopy (TEM), a microhardness tester, and tribemates to determine the optimal process parameters for creating Ni-W-Al₂O₃ nanocomposite coatings. The results indicated that the jet rate, Al₂O₃ content, ultrasonic power, interaction terms, and quadratic terms significantly influenced the microhardness of the coatings. The optimized process parameters using the JMP software were a jet rate of 3.71 m/s, Al₂O₃ content of 15.38 g/L, and ultrasonic power of 210 W. Furthermore, the coatings produced under these optimal conditions showed low wear rates and friction coefficients, a refined grain size, a dense surface topology, and a high microhardness (724.9 HV). Full article

The most common type of well in the Fuling shale gas field is the long horizontal section well. Once the energy attenuates, it is difficult to discharge the accumulated liquid. So, it is particularly important to determine the time of accumulation. Through indoor experiments, it was observed that droplets in the gas core flowing under critical conditions and the liquid film adhering to the tube wall cannot be ignored. It was also discovered that the liquid phase on the tube wall can form fluctuations due to the shear effect of the gas phase. Based on the observed distribution of gas–liquid phases in experiments, a critical liquid-carrying velocity calculation method considering the coexistence of droplets and liquid films, as well as the frictional resistance coefficient at the gas–liquid interface under wave morphology, was established. Integrating production data from 106 wells at home and abroad, as well as testing data from the Fuling example well, the new model was validated. The results showed that the new model can accurately diagnose fluid accumulation in different gas fields, with an accuracy rate of 86.8%, and it can provide an accurate diagnosis for fluid accumulation in gas wells in different water-producing gas fields. Full article

Friction has a significant impact on chip formation, so modeling it accurately is crucial in numerical cutting simulations. However, there is still controversy regarding the application scope and effectiveness of various friction models. A two-dimensional orthogonal cutting thermomechanical coupled finite element model is established. Critical strain values, recrystallization temperature, and recrystallization flow stress are introduced, and a power-law-modified softening coefficient is used to modify the standard Johnson–Cook constitutive model to simulate material mechanical properties. Zorev’s friction model, velocity-dependent friction model, and temperature-dependent friction model are separately employed to describe the friction behavior between the tool and workpiece. The contact and friction characteristics between the workpiece and tool, material damage, and temperature field are evaluated. Predicted cutting forces are compared and analyzed with experimental values. The friction coefficient can adjust the contact length between the tool and chip, the high-temperature range on the tool surface, and the fluctuation of temperature throughout the entire cutting process. The friction coefficient is more sensitive to sliding velocity, and the temperature distribution is more sensitive to the friction model than to different working conditions. Whether by modifying the friction coefficient or maximum friction shear stress, and regardless of whether adding parameters affected by velocity or temperature changes the fluctuation range, period, and local peaks of the cutting force prediction curve, improving the accuracy of predictions within certain working condition ranges to some extent. However, the overall trend of error fluctuations obtained from these friction models is similar, and the accuracy of predictions from these friction models tends to become more inaccurate with increasing cutting thickness. Full article

To significantly improve the tribological performance of epoxy resin (EP), a novel h-BN/MoS₂ composite was successfully synthesized using spherical MoS₂ particles with lamellar self-assembly generated through the calcination method, followed by utilizing the “bridging effect” of a silane coupling agent to achieve a uniform and vertically oriented decoration of hexagonal boron nitride (h-BN) nanosheets on the MoS₂ surface. The chemical composition and microstructure of the h-BN/MoS₂ composite were systematically investigated. Furthermore, the enhancement effect of composites with various contents on the frictional properties of epoxy coatings was studied, and the mechanism was elucidated. The results demonstrate that the uniform decoration of h-BN enhances the chemical stability of MoS₂ in friction tests, and the MoS₂ prevents oxidation and maintains its self-lubricating properties. Consequently, due to the protective effect of h-BN and the synergistic interaction between h-BN and MoS₂, the 5 wt % h-BN/MoS₂ composite exhibited the best friction and wear resistance when incorporated into EP. Compared to pure EP coatings, its average friction coefficient and specific wear rate (0.026 and 1.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹, respectively) were significantly reduced. Specifically, the average friction coefficient decreased by 88% and the specific wear rate decreased by 99%, highlighting the superior performance of the h-BN/MoS₂-enhanced epoxy composite coating. Full article

This study investigates the properties of diamond-like carbon (DLC) coatings deposited onto a Ti6Al4V titanium alloy using plasma-assisted chemical vapor deposition (PACVD). The research encompasses adhesion tests, hardness, surface characterization, as well as corrosion and tribological evaluations. Artificial saliva was employed as both the lubricating and corrosive medium. Microscopic examination revealed a uniform coating with a thickness of about 3.2 µm. Scratch test results indicated that the deposited DLC coating exhibited superior adhesion, lower frictional resistance, and reduced wear compared to the titanium alloy. The coating deposition increased the hardness of the Ti6Al4V alloy by about 75%. Friction coefficients, measured under dry and lubricated conditions, were approximately 80% lower for the DLC-coated samples. Corrosion studies revealed that both the coated and uncoated surfaces demonstrated typical passive behavior and high corrosion resistance in artificial saliva. For DLC coatings, the corrosion current density and the corrosion rate were reduced by 85%. Microscopic observations of wear tracks following tribological and scratch tests confirmed the inferior wear and scratch resistance of the titanium alloy relative to the DLC coating. Under both dry and lubricated conditions (with artificial saliva), the volumetric wear rate of the titanium alloy was over 90% higher than for the DLC coating. Full article

This paper studies the coatings deposited on a 65G steel substrate by electric arc metallization using a 30KhGSA wire. The properties of the coatings obtained at 30 V, 40 V and 45 V are discussed, including their microstructure, porosity, microhardness, coefficient of friction and corrosion resistance. The experiments showed that the coatings possess a layered structure formed by sequential deposition of metal microdroplets. It was found that the increase in voltage favors the decrease in porosity, increase in layer density, increase in microhardness and improvement in wear resistance and corrosion resistance. At maximum voltage (45 V), there are optimum performance characteristics, such as minimal porosity (1.36%), high microhardness (305 HV) and improved corrosion resistance. The main defects of the coatings, including pores and oxide inclusions, which are formed during the sputtering process and depend on the kinetic energy of the microdroplets, were identified. These defects affect the mechanical and protective properties of the coatings. Full article

The main shaft seal of offshore wind power equipment is one of the key components of wind power systems. However, wear issues between the seals and the main shaft caused by the intrusion of particulate matter in the environment have become a key factor affecting the service life of the equipment. To improve the surface performance of the main shaft, this study used laser cladding technology to prepare an Fe55 coating on the surface of QT-500 components. Through the wear experiments on HNBR seal pairs with the main shaft under different load conditions, this study thoroughly investigated the impact of the coating on frictional coefficients, wear mechanisms, and the wear morphology of metal surfaces. The experimental results show that the average hardness of the Fe55 coating is 533 HV, which is about 2.3 times the hardness of the substrate, and as the loading force increases, the wear form of the QT-500 metal changes from being dominated by pits to being dominated by furrows. In contrast, the wear form of the Fe55 coating is more inclined to furrows, and no pit formation is observed, indicating that the coating has improved the wear resistance of the surface. The frictional coefficient of the HNBR pair with the metal decreases with increasing load, and the frictional coefficient of the coating is lower than that of the substrate. As the loading increases, the wear morphology of the rubber surface transitions from furrows to pits, and the wear mechanism becomes abrasive wear. Full article

With the continuous increase in the thermal power of electronic devices, air cooling is becoming increasingly challenging in terms of meeting heat dissipation requirements. Liquid cooling media have a higher specific heat capacity and better heat dissipation effect, making it a more efficient cooling method. In order to improve the heat dissipation effect of liquid cooling, a TPMS structure with a larger specific surface area, which implicit function parameters can control, can be arranged in a shape manner and it is easy to expand the structural design. It has excellent potential for application in the field of heat dissipation. At present, research is still in its initial stage and lacks comparative studies on liquid cooled convective heat transfer of TPMS structures G (Gyroid), D (Diamond), and P (Primitive). This paper investigates the heat transfer performance and pressure drop characteristics of a sheet-like microstructure composed of classic TPMS structures, G (Gyroid), D (Diamond), and P (Primitive), with a single crystal cell length of 2π (mm), a cell number of 1 × 1 × 5, and a microstructure size of 2π (mm) × 2π (mm) × 22π (mm) using a constant temperature surface model. By analyzing the outlet temperature $t_{out}$, structural pressure $p$, average convective heat transfer coefficient $h_0$, Nusselt number $Nu$, and average wall friction factor $f$ of the microstructure within the speed range of 0.01–0.11 m/s and constant temperature surface temperature is 100 °C, the heat transfer capacity D > G > P and pressure drop D > G > P were obtained (the difference in pressure drop between G and P is very small, less than 20 Pa, which can be considered consistent). When flow velocity is 0.01 m/s, the maximum temperature difference at the outlet of the four structures reached 17.14 °C, and the maximum difference in wall friction factor $f$ reached 103.264, with a relative change of 646%. When flow velocity is 0.11 m/s, the maximum pressure difference among the four structures reached 8461.84 Pa, and the maximum difference in $h_0$ reached 7513 W/(m²·K), with a relative change of 63.36%; the maximum difference between Nu reached 76.32, with a relative change of 62.09%. This paper explains the reasons for the above conclusions by analyzing the proportion of solid area on the constant temperature surface of the structure, the porosity of the structure, and the characteristics of streamlines in the microstructure. Full article

EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage to bearings. This study evaluates the tribological performance of four types of greases—PUEs, PUPao, PUEth (polyurea-based), and LiPAO (lithium–calcium complex-based)—to determine their suitability for electric motor bearings. Key performance metrics include tribological properties, electrical resistivity, leakage, bearing noise, and wear behavior. A four-ball wear test ranks the greases by scar diameter as PUPao < PUEs < PUEth < LiPAO, while the coefficient of friction is observed in the range of 0.15–0.18, with LiPAO exhibiting the lowest friction. Electrical resistivity tests reveal that PUEs grease has the lowest resistivity. Electrical leakage tests, conducted with a voltage differential across bearings, assess pitting damage, with PUEth and LiPAO showing evidence of surface pitting. Optical microscopy and scanning electron microscopy analysis is carried out to examine the pitting. In bearing noise tests, PUEs demonstrates the lowest noise levels, whereas LiPAO produces the highest. Visual and microscopic examination of the greases further characterizes their lubricating properties. Based on overall performance, the greases are ranked in suitability for electric motor applications as PUEs > PUPao > PUEth > LiPAO. The findings highlight the critical need for selecting appropriate grease formulations to ensure optimal bearing performance under varying operational conditions. Full article

At present, the improvement of anti-wear performance of piston rings remains a challenge. In this article, Ni-SiC composite coatings fabricated at 3, 9, and 15 g/L SiC were denoted as NSc-3, NSc-9, and NSc-15 coatings. Meanwhile, the influence of SiC concentration on the surface morphology, phase structure, microhardness, and anti-wear performance of electrodeposited Ni-SiC composite coatings were investigated utilizing scanning electron microscopy, X-ray diffraction, a microhardness tester, and a friction–wear tester, respectively. The SEM images presented NSc-9 coatings with a compact, flat, or cauliflower-like surface morphology. The cross-sectional morphology and EDS results showed that the Si and Ni elements were uniformly distributed in the NSc-9 coatings with dense and flat microstructures. Moreover, the average grain size of the NSc-9 coatings was only 429 nm. Furthermore, the microhardness and indentation path of the NSc-9 coatings were 672 Hv and 13.7 μm, respectively. Also, the average friction coefficient and worn weight loss of the NSc-9 coatings were 0.46 and 29.5 mg, respectively, which were lower than those of the NSc-3 and NSc-15 coatings. In addition, a few shallow scratches emerged on the worn surfaces of the NSc-9 coatings, demonstrating their outstanding anti-wear performance when compared to the NSc-3 and NSc-15 coatings. Full article

Adding alloying elements to binary nitrides enables the design of hard and tough coatings. To improve the mechanical and tribological performances of TiN-based coatings, La atoms were added to TiAlN coatings to form TiAlLaN coatings. Magnetron sputtering was conducted to prepare the TiAlLaN coatings. Thereafter, scanning electron microscopy (SEM), x-ray diffraction (XRD), nano-indentation, and a tribometer were utilized to test their microstructure, phases, and mechanical and tribological performances. Next, this study analyzed how lanthanum affected the microstructure and tribological performances of the TiAlLaN coatings. Incorporating La atoms in TiAlN coatings reduced the crystallite size and enhanced the coating toughness and hardness. The hardness H and elastic modulus E of the TiAlLaN coatings first increased and then decreased with the increase in La. Meanwhile, the coatings had improved wear and friction properties. The increased H/E and H³/E² levels, which have been considered to reflect the hard coating’s toughness, were acquired based on the TiAlLaN coating, possessing enhanced hardness (19.8 GPa). The coefficient of friction and the wear rates of the coatings reduced and then increased with the increase in La. The TiAlLaN coating with 1.4 % of lanthanum had the lowest friction coefficient and wear rate of around 0.383 and 1.59 × 10⁻⁸ mm³/N·m, respectively, corresponding to a higher H/E (~0.086) and H³/E² (~0.147 GPa). Adding an appropriate amount of La can substantially enhance the TiAlN coating’s tribological and mechanical properties. The TiAlLaN coating with remarkable characteristics may be applied to a steel substrate. Full article