Search Results (18)

The rapid growth of electric vehicles and electrified systems has increased the risk of bearing failures due to combined mechanical and electrical stresses. This study investigated the performance of hexagonal boron nitride nanoparticle-enhanced lithium grease under electrified conditions. Experiments based on a Taguchi L9 orthogonal array were conducted on deep groove ball bearings using a full-scale test rig at 1200 rpm with varying loads (100–300 N), currents (6–10 A), and hBN concentrations (0.1–1 wt.%). The tribo-electrical performance of nano-enhanced grease was compared with the base grease and commercial grease. It was observed that the base grease exhibited superior performance with a lower current flow, reduced vibration, and minimal surface degradation. In contrast, the hBN-enhanced grease exhibited inferior tribo-performance, with high vibrations and surface damage in electrified conditions. The surface analysis revealed features morphologically similar to white etching areas and micro-pitting. The FTIR results indicated grease degradation, while ICP-OES confirmed higher wear debris generation in the commercial and hBN-added greases. The present work indicates that additives like hBN nanoparticles do not necessarily improve performance under electrified conditions, making it important to consider the type of additives to be added during lubricant formulation. Thus, the findings emphasize the importance of lubricant formulation for controlling electrically induced bearing failures and provide insights for developing advanced greases for electric machinery applications. Full article

This study investigated the relationship between the surface microstructure of pearlite steel wheels and the formation of fatigue cracks during the braking process by using a full-size wheel braking test rig. After fatigue failure, the surface microstructural evolution and fatigue crack initiation and propagation of the wheel sample were systematically analyzed by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results showed that after braking of 1572 cycles, a large number of fatigue cracks formed at the wheel tread, which caused the wheel to break. After fatigue failure, some dark areas formed at the wheel tread, which were composed of Fe₃O₄ compounds. This indicates that severe oxidation was produced at the wheel tread during braking due to the high temperature. After fatigue failure, a continuous thermal white etching layer (T-WEL) was formed in some areas of the wheel tread, while crescent-shaped T-WEL was found in other areas. The microstructure of the T-WEL was composed of martensite phase. The rapid increase and decrease in temperature at the wheel tread during the braking process caused martensitic transformation at the wheel tread. The hardness of the sample reached to about 900 HV in WEL and it reduced with the increase in distance from the surface. The cracks were initiated from the surface and gradually propagated into the matrix. However, the crack propagation mode in the continuous T-WEL and crescent-shaped T-WEL was different. In the continuous T-WEL, the continuous T-WEL of the wheel can be peeled off during the braking wear process, and then the crack was gradually propagated into the matrix in the T-WEL peeled area. As for the crescent-shaped T-WEL, due to the large hardness difference between T-WEL and pearlite, the crack initiated at the interface between the T-WEL and pearlite and gradually propagated into the matrix. Full article

Quantum dots (QDs) have tremendous potential for next-generation displays due to their high color purity, photoluminescence efficiency, and power efficiency. In this work, we present a simple and cost-effective method for fabricating flexible single- and multiple-layer films, and they can be detached and attached to the outside of OLEDs as a light-scattering and color-conversion layer. Light extraction efficiency is enhanced by forming low-density structures by using the reactive ion etching (RIE) process. As a result, the QD/PDMS composite film allowed for color conversion and achieved an excellent light extraction efficiency of up to 9.2%. Furthermore, the QD/PDMS composite film and greenish-blue OLED produced white light (CIEx,y = 0.28, 0.41), demonstrating the potential for application in broad areas, from flexible displays to lighting. The method provides a simple and cost-effective alternative to conventional processes. Full article

Deep groove ball bearings are important mechanical elements in the automotive and process industries, particularly in electric motors. One of the primary reasons for their failure is lubricant degradation due to stray shaft current. Thus, the present work exhibited the failure of bearings under simulated lubricated conditions similar to those of real time bearings failing in presence of stray electric current. The test was conducted using a full bearing test rig with an applied radial load, 496 N, an alternating current, 10 A, and a rotation of 2000 rpm for 24 h. The bearings (6206 series) were greased using two commercially available ester-polyalphaolefin oil-based greases with viscosity 46–54 cSt (Grease 1) and 32–35 cSt (Grease 2, also contained aromatic oil). The optical microscopic images of the bearing raceways after the tribo test indicated the superior performance of Grease 1 compared to Grease 2, with lesser formation of white etching areas, micro-pitting, spot welds, and fluting on the surfaces of the bearings. Additionally, 80% less vibrations were recorded during the test with Grease 1, indicating a stable lubricating film of Grease 1 during the test as compared to Grease 2. Furthermore, a higher extent of Grease 2 degradation during the tribo test was also confirmed using Fourier transform infrared spectroscopy. Statistical analysis (t-test) indicated the significant variation of the vibrations produced during the test with electrified conditions. The present work indicated that the composition of the greases plays a significant role in controlling the bearing failures. Full article

This study evaluated the bone-to-implant contact (BIC) of various surface-treated dental implants using high-resolution micro-CT in rabbit bone, focusing on the effects of different treatments on osseointegration and implant stability before and after bone demineralization. Six male New Zealand White rabbits were used. Four implant types were tested: machined surface with anodizing, only etching, sandblasting with Al₂O₃ + etching, and sandblasting with TiO₂ + etching. Implants were scanned with high-resolution micro-CT before and after demineralization. Parameters like implant volume, surface area, and BIC were determined using specific software tools. During demineralization, the BIC changed about 6% for machined surface with anodizing, 5% for only etching, 4% for sandblasting with Al₂O₃ + etching, and 10% for sandblasting with TiO₂ + etching. Demineralization reduced BIC percentages, notably in the machined surface with anodizing and sandblasting with TiO₂ + etching groups. Etching and sandblasting combined with etching showed higher initial BIC compared to anodizing alone. Demineralization negatively impacted the BIC across all treatments. This study underscores the importance of surface modification in implant integration, especially in compromised bone. Further research with larger sample sizes and advanced techniques is recommended. Full article

Surface treatment of implants facilitates osseointegration, with nanostructured surfaces exhibiting accelerated peri-implant bone regeneration. This study compared bone-to-implant contact (BIC) in implants with hydroxyapatite (HA), sand-blasted and acid-etched (SLA), and SLA with calcium (Ca)-coated (XPEED^®) surfaces. Seventy-five disk-shaped grade 4 Ti specimens divided into three groups were prepared, with 16 implants per group tested in New Zealand white rabbits. Surface characterization was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), digital microscopy, and a contact angle analyzer. Cell viability, proliferation, and adhesion were assessed using MC3T3-E1 cells. Apatite formation was evaluated using modified simulated body fluid (m-SBF) incubation. After 4 weeks of healing, the outcomes reviewed were BIC, bone area (BA), removal torque tests, and histomorphometric evaluation. A microstructure analysis revealed irregular pores across all groups, with the XPEED group exhibiting a nanostructured Ca-coated surface. Surface characterization showed a crystalline CaTiO₃ layer on XPEED surfaces, with evenly distributed Ca penetrating the implants. All surfaces provided excellent environments for cell growth. The XPEED and SLA groups showed significantly higher cell density and viability with superior osseointegration than HA (p < 0.05); XPEED exhibited the highest absorbance values. Thus, XPEED surface treatment improved implant performance, biocompatibility, stability, and osseointegration. Full article

Damage in bearings is closely associated with the presence of microstructural alterations, known as white etching areas (WEAs) and white etching cracks (WECs). One of the main reasons for the creation of these microstructural alterations is the presence of defects in the material, such as non-metallic inclusions. Manganese sulfides and aluminum oxides are widely reported in the literature as the most common types of non-metallic inclusions found in bearing steels. This study classifies 280 non-metallic inclusions in an investigated bearing steel according to several criteria: bonded/debonded with the matrix, size, shape, orientation angle, depth below the raceway surface, and chemical composition. Contrary to the findings in the literature, this investigation reports that the chemical composition of the inclusion (MnS + Al₂O₃) is of secondary importance when considering factors for damage initiation. The orientation of the microstructural alterations is observed to coincide with the high-stress regions, indicating a relation between the formation of butterfly wings and the white etching crack. In our investigation, butterfly wings typically exhibit a 45-degree pattern originating from the non-metallic inclusions. Conversely, the white etching crack starts from the non-metallic inclusion at a shallower angle in correspondence to the raceway. This can be attributed to the stress state, which corresponds to a region where extensive white etching cracks are formed. In conclusion, the microstructural observations demonstrate that the state of non-metallic inclusion—i.e., whether they are bonded or not to the steel matrix—plays an essential role in initiating rolling contact fatigue damage. Full article

The tribological contact between raceways and rolling elements is essential for rolling bearing performance and lifetime. The geometrical description of these contacts is well known and can be used in several mechanical simulation tools. The material description, especially of the near-surface volume after interaction with lubricants, is not as simple. In particular, the Schaeffler FE8-25 test with cylindrical roller thrust bearings exhibits different failure modes depending on the lubricant chemistry. The main failure mechanisms of this test are sub-surface fatigue damage due to WECs (White Etching Cracks) and/or surface-induced fatigue damage (SIF). The harsh test conditions with mixed friction at high speeds and multiple slip conditions over the raceway width additionally provides different tribological conditions on a small area. This leads finally to the formation of certain tribological layers on the raceway because of the interaction of the surface with the lubricant chemistry under local frictional energies, which are worth investigating. The characterization of the layers was performed by the two less time-consuming, spatially resolved analysis methods of µXRF and ATR FTIR microscopy adapted by Schaeffler. This paper shows the results of this research and offers new approaches to optimizing rolling bearing testing and predicting the risk of early failures. Full article

The problem of White Etching Cracks (WEC) leading to failures in the life cycle of industrial and automotive drive trains has existed for more than 30 years. Many parameters leading to WEC, such as the presence of electricity, unfavorable lubricants, and other factors, have been identified by the use of test rigs. However, since (a) within lifecycle operation these impacts appear incidentally, and (b) the identified impacts stimulate each other as stated in WEC research, the appearance of WEC in a drive train is impossible to predict for any given application. This difficulty causes WEC to be a serious problem. Obtaining reliable failure prediction rates using construction guidelines is still impossible, resulting in warranty claims. The aim of this paper is, first, to establish a routine to determine if and how lubricants could be described numerically with respect to their susceptibility toward electrical fields and to see how this factor could be added in a later stage to construction guidelines. Second, this paper aims to give advice to the applicant in terms of countermeasures. Currently, as predictors are missing, extensive and time-consuming testing is required. Contradictory test results in the field of application, indicate the need for fundamental parameters to determine in which circumstances the application is exposed to WEC risk and to suggest countermeasures. The current study presents a simulation method based solely on the chemical structure of lubricant components, investigating the appearance of WEC and their response to increasing electrical fields. The results show a clear pattern in WEC criticality with respect to lubricants: if two or more components present in the lubricant create clusters through their dipolar interaction, an apparent WEC risk could be accurately predicted apart from test rig results. These clusters are charged like one big particle in an early stage of electrical field exposure. As a result, the surface area increases, facilitating a higher uptake of charge. The incidental breakdown of this charge is assumed. As the charge of a cluster is higher than that of single molecules, WEC critical lubricants are subjected to this pattern. The study validates these results by comparing them using lubricants known to be critical with respect to WEC, suggesting further tests in the near future. Despite the fact that some lubricants seem more critical than others related to WEC, each lubricant clearly might lead to WEC under given conditions. Thus, constructing guidelines for a prediction routine is essential. Full article

Oxygen vacancy manipulation and hierarchical morphology construction in oxygen-containing semiconductors have been demonstrated to be effective strategies for developing high efficiency photocatalysts. In most studies of bismuth-based photocatalysts, hierarchical morphology and crystal defects are achieved separately, so the catalysts are not able to benefit from both features. Herein, using boiling ethylene glycol as the treatment solution, we developed an etching-recrystallization method for the fabrication of 3D hierarchical defective BiOCl at ambient pressure. The target hierarchical 3D-BiOCl is composed of self-assembled BiOCl nanosheets, which exhibit a hexagonal prism-like morphology on a micron scale, while simultaneously containing numerous oxygen vacancies within the crystal structure. Consequently, the target catalyst was endowed with a higher specific surface area, greater light harvesting capability, as well as more efficient separation and transfer of photo-excited charges than pristine BiOCl. As a result, 3D-BiOCl presented an impressive photocatalytic activity for the degradation of tetracycline hydrochloride in both visible light and natural white light emitting diode (LED) irradiation. Moreover, an extraordinary recycling property was demonstrated for the target photocatalyst thanks to its hierarchical structure. This study outlines a simple and energy-efficient approach for producing high-performance hierarchically defective BiOCl, which may also open up new possibilities for the morphological and crystal structural defect regulation of other Bi-based photocatalysts. Full article

Due to its high hardness and high transmittance, ultra-white glass has a strong application prospect in the fields of optoelectronics industry and experimental instruments. However, because of its brittleness, it was still a difficult problem in the machining industry. Surface modification provides a basic research idea for ultra-white glass microstructure processing. An effective method to obtain surface modified area on ultra-white glass was presented. The modified zone on the surface of ultra-white glass was induced by the technique of coating and femtosecond laser-assisted chemical etching. The method combines vacuum coating with femtosecond laser irradiation. Next, the modified glass was processed with highly selective potassium hydroxide solution. In order to control the surface size more efficiently, the optimization experiment of laser parameters and chemical parameters on the machining process was carried out. The experimental results show that the method made the surface modification of ultra-white glass more easily and provides basic research for fabricating microchannels on the material. Full article

Bearings are vital components that are widely used in modern machinery. Although usually manufactured with high-strength steels, bearings still suffer from rolling contact fatigue where unique microstructural alterations take place beneath the contact surface as a result of the complex stress state. Studying these microstructural alterations is a hot research topic with many efforts in recent decades. In this respect, the key information regarding four major types of microstructural alterations, white etching areas/white etching cracks, dark etching regions, white etching bands and light etching regions is reviewed regarding the phenomenology and formation mechanisms. Then, classical and state-of-the-art models are established to predict their formation and are summarised and evaluated. Based on the current research progress, several key questions and paradoxes for each type of microstructural alteration are raised, suggesting possible research directions in this field. Full article

The reliability of rolling element bearings has been substantially undermined by the presence of parasitic and stray currents. Electrical discharges can occur between the raceway and the rolling elements and it has been previously shown that these discharges at relatively high current density levels can result in fluting and corrugation damages. Recent publications have shown that for a bearing operating at specific mechanical conditions (load, temperature, speed, and slip), electrical discharges at low current densities (<1 mA/mm²) may substantially reduce bearing life due to the formation of white etching cracks (WECs) in bearing components, often in junction with lubricants. To date, limited studies have been conducted to understand the electrical discharges at relatively low current densities (<1 mA/mm²), partially due to the lack of robust techniques for in-situ quantification of discharges. This study, using voltage measurement and electrostatic sensors, investigates discharges in an oil-lubricated steel-steel rolling contact on a TE74 twin-roller machine under a wide range of electrical and mechanical conditions. The results show that the discharges events between the rollers are influenced by temperature, load, and speed due to changes in the lubricant film thickness and contact area, and the sensors are effective in detecting, characterizing and quantifying the discharges. Hence, these sensors can be effectively used to study the influence of discharges on WEC formation. Full article

The aim of this study was to investigate the behavior of dental-derived human mesenchymal stem cells (d-hMSCs) in response to differently surface-treated implants and to evaluate the effect of d-hMSCs on local osteogenesis around an implant in vivo. d-hMSCs derived from alveolar bone were established and cultured on machined, sandblasted and acid-etched (SLA)-treated titanium discs with and without osteogenic induction medium. Their morphological and osteogenic potential was assessed by scanning electron microscopy (SEM) and real-time polymerase chain reaction (RT-PCR) via mixing of 5 × 10⁶ of d-hMSCs with 1 mL of Metrigel and 20 μL of gel-cell mixture, which was dispensed into the defect followed by the placement of customized mini-implants (machined, SLA-treated implants) in New Zealand white rabbits. Following healing periods of 2 weeks and 12 weeks, the obtained samples in each group were analyzed radiographically, histomorphometrically and immunohistochemically. The quantitative change in osteogenic differentiation of d-hMSCs was identified according to the type of surface treatment. Radiographic analysis revealed that an increase in new bone formation was statistically significant in the d-hMSCs group. Histomorphometric analysis was in accordance with radiographic analysis, showing the significantly increased new bone formation in the d-hMSCs group regardless of time of sacrifice. Human nuclei A was identified near the area where d-hMSCs were implanted but the level of expression was found to be decreased as time passed. Within the limitations of the present study, in this animal model, the transplantation of d-hMSCs enhanced the new bone formation around an implant and the survival and function of the stem cells was experimentally proven up to 12 weeks post-sacrifice. Full article

During the bearing service, a series of microstructural evolutions will arise inside the material, such as the appearance of feature microstructures. The essential reason for the microstructural evolution is the cumulative effect of cyclic stress. The Hertz Contact formula is usually adopted to calculate the internal stress, and there is a correlation between the shape and distribution of the feature microstructure and the stress distribution. But it is insufficient to explain the relationship between the morphology of feature microstructures and the rolling direction, such as specific angles in butterfly and white etching bands. The rolling phenomenon will cause the asymmetry of stress distribution in the material, which is the source of the rolling friction coefficient. Moreover, slipping or microslip will produce additional stress components, which also cause the asymmetry of the stress field. However, there is no experimental or theoretical explanation for the relationship between the asymmetry of the stress field and the feature microstructure. According to the current theory, the appearance of feature microstructures is caused by stress with or without rolling. Therefore, it is of great significance to study the formation mechanism: whether feature microstructures will appear in the uniaxial cyclic compression stress field without rolling. In this paper, uniaxial cyclic compressive stress was loaded into a plate-ball system and a cylinder system. The characteristics of microstructural change of bearing steel (GCr15) were studied. It was found that the hardness of the material increased after the cyclic compressive load, and the inclusions interacted with the matrix material. In the local microregion a white etching area was found, although the scale is very small. No large-scale feature microstructures appeared. Other phenomena in the experiment are also described and analyzed. For example, the production of oil film in the contact area and the changing law of alternating load. Full article