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The use of thermite to aid spacecraft demise during atmospheric re-entry has been investigated in the ESA-TRP SPADEXO project. An experimental campaign in DLR's L2K arc-heated wind tunnel facility was dedicated to explore the Thermite-for-Demise concept. Steel mock-ups of a ball bearing unit, partially filled with thermite, were placed in L2K. The breadboards were then exposed to an air flux simulating the typical conditions that characterize spacecraft re-entry. In this paper, the key results of the tests are presented. The dispersion of a mechanically activated fraction of thermite proved to be effective in controlling the overall charge ignition temperature. Thermite-induced demise was experimentally verified in the wind tunnel. The SCARAB software was extended and used to rebuild the retrieved thermal data. The results of the simulations were in good agreement in both predicting the ignition timing and the effects of the thermite charge on the sample. • Thermite-induced demise was verified in hypersonic wind tunnel conditions. • Mechanical activation can tune thermite passive ignition in space-like environment. • Numerical models can describe and foresee thermite-induced demise. [ABSTRACT FROM AUTHOR]

Introduction With similar prevalence to injuries from fires, stings, and natural disasters, soft tissue injuries may occur from fireworks, industrial accidents, or other explosives. Surgeons are less familiar with treating high-velocity penetration from small debris, which may increase the chance of infection and subsequent fatality. Penetration risk curves have been developed to predict V50, the velocity with 50% probability of penetration, for various sized projectiles. However, there has been limited research using nonmetallic materials to achieve lower density projectiles less than 1 g cm−2, such as sand or rocks. Material and Methods To emulate the size and density of these energized particles, 14 ball bearings of stainless steel, silicon nitride, or Delrin acetal plastic ranging from 1.59 mm (1/16") to 9.53 mm (3/8") with sectional densities between 0.3 g cm−2 and 5  g cm−2 were launched toward porcine legs at a range of velocities to determine the penetration thresholds. High-speed videography was captured laterally at 40 kHz and impact velocity was captured using a physics-based tracking software. A generalized linear model with repeated measures and a logit link function was used to predict probability of penetration for each projectile. A total of 600 impacts were conducted to achieve at least 15 penetrating impacts for each projectile over a range of velocities. Results Higher impact velocities were required to penetrate the skin as sectional density of the projectile decreased, and the relationship between velocity and sectional density exhibited an exponential relationship (V 50, |$ = 184.6*S{D^{ - 0.385}}$|⁠ , R 2 = 0.95) with substantial change for nonlinearity in sectional densities ranging from 0.3 g cm−2 to 1  g cm−2. Compared to previous studies, the empirical relationship was consistent in the linear region (2-5  g cm−2), and novel experimentation filled in the gaps for sectional densities less than 1  g cm−2, which expressed more nonlinearity than previously estimated. For low-density projectiles with diameters of 1.59 (1/16") or 3.18 (1/8"), 32 impacts were lodged into the epidermis but did not penetrate through the dermis; however, penetration was defined as displacement into or through the dermis. Conclusions These experimental results may be used to develop and validate finite element simulations of low-density projectile impacts to address complex, multivariate loading conditions for the development of protective clothing to reduce wounding and subsequent infection rates. [ABSTRACT FROM AUTHOR]

Micro-Computed Tomography (µCT) systems are used for examining the internal structures of various objects, such as material samples, manufactured parts, and natural objects. Resolving fine details or performing accurate geometric measurements in the voxel data critically depends on the precise calibration of the µCT systems geometry. This paper presents a calibration method for µCT systems using projections of a calibration phantom, where the coordinates of the phantom are initially unknown. The approach involves detecting and tracking steel ball bearings and adjusting the unknown system geometry parameters using non-linear least squares optimization. Multiple geometric models are tested to verify their suitability for a self-calibration approach. The implementation is tested using a calibration phantom captured at different magnifications. The results demonstrate the system's capability to determine the geometry model parameters with a remaining error on the detector between 0.27 px and 0.18 px. Systematic errors that remain after calibration, as well as changing parameters due to system instabilities, are investigated. The source code of this work is published to enable further research. [ABSTRACT FROM AUTHOR]

Helical rolling (HR) with high temperature is an efficient forming process to produce bearing steel balls with diameter more than 25 mm. This article discusses the advantages and disadvantages of two HR roller designing methods: single side variable lead method and double side variable lead method. Finite element (FE) simulations of HR processes based on the two methods indicate that the double side variable lead method has higher forming accuracy and is more suitable for forming bearing steel balls. Experiments based on the double side variable lead method are carried out to verify the validity of FE model. The distributions of strain and stress, temperature evolution and rolling force parameters are analyzed based on the FE method. Axial motion analysis shows that the axial velocity of the rolled piece is closely related to axial push velocity of roller convex rib. Microstructure evolution indicates that grains near ball connector area and ball surface get refined due to drastic plastic deformation. The forming accuracy of HR process including radius deviations and ovalities of three cross sections are measured. The statistical results indicate that radius deviation of rolled balls can be controlled within 0.1 mm and ovality can be as small as within 1%. Effects of roller parameters on forming accuracy are analyzed including volume coefficient at groove closed position, forming zone length and starting height of convex rib. Forming accuracy gets better with the increase of volume coefficient, the increase of forming zone length, and the decrease of staring height of convex rib. [ABSTRACT FROM AUTHOR]

The contact interface between the bearing shells and crankshafts in marine internal combustion engines is subjected to complex forces during operation, and improper lubrication can easily cause adhesion, scratches and cracks on the journal. To extend the service life of bearing shells, the polyamide imide and polytetrafluoroethylene (PAI/PTFE) composite coatings were prepared on the surface of bearing shells, and the effect of MoS2 particles on the friction performance of PAI/PTFE composite coatings was explored. Composite coatings with different MoS2 mass fraction were prepared on the surface of Al-Sn-Cu alloy bearing material by spray-sintering method. Using bearing steel ball as friction pair, the tribological properties of the composite coatings were investigated at 3 N,4 N, and 5 N loads under dry friction and oil lubrication. The results show that under dry friction, the friction coefficient of the composite coating with a MoS2 mass fraction of 2% is reduced by more than 80%, and the wear is reduced by more than 90%. The maximum reduction in friction coefficient under oil lubrication is 67%. The results of SEM and EDS analysis indicate that a coating containing 2% MoS2 will generate a uniform sulfide layer on the contact surface of the steel ball, which can protect the coating and improve its stability. By comparing the friction coefficient, wear, and wear scar morphology of coatings with different MoS2 content, the optimal ratio of the coatings is obtained. It is shown that an appropriate amount of MoS2 can improve the stability of the coating friction film and reduce friction and wear. [ABSTRACT FROM AUTHOR]

The effect of variable DC bearing current amplitude, bearing current polarity, mechanical force, rotation speed, bearing temperature, and number of the balls on the fluting in an axial ball bearing type 51208 is investigated under DC currents. The results are obtained from two different test setups with two different lubricants (mineral-oil-based grease and polyglycol oil). The speed varies between 100 rpm and 2000 rpm, the axial bearing force between 200 N and 2400 N, the DC current amplitude between 0.5 A and 20 A, the bearing temperature between 29 °C and 80 °C, the number of steel balls per bearing between 3 and 15, and the test duration between 6 h and 168 h. The results show that with a higher bearing current density and/or a higher bearing speed, a lower bearing force and/or a lower bearing temperature, a bigger number of roller elements, but also at a negative polarity of a DC electric bearing current, the occurring of fluting is more probable and occurs at an earlier stage of operation. [ABSTRACT FROM AUTHOR]

The tribological characteristics of a below 1 mm micro ball bearing comprising steel disc and cages coated with thin copper and silver films were investigated. Electroplating and laser cutting were used to manufacture used elements. Friction was measured using a linear stage and an adapted version of a friction-loop method. The obtained results show an interesting relationship between the geometric properties of the micro scale thrust bearing and their performance and operational stability, which can be correlated to similar relationships observed in the macro scale. The most optimal design of the bearing showed stable operation, with the simplified rolling resistance coefficient in the range 0.002 to 0.003, independently of applied load, which was in range 150 mN to 1500 mN. The possibility of creating easily manufacturable micro ball bearings with a low rolling resistance coefficient comprised solely of cheap and sturdy elements was shown. [ABSTRACT FROM AUTHOR]

Aluminum is a very commonly used material at present, and roughly half of the produced aluminum products undergo forming during manufacturing. Galling is a severe form of wear that occurs during sheet metal forming operations and is a common failure mode of materials in sliding contact; however, the causes and mechanisms of galling are poorly understood. In this work, sliding wear experiments were conducted to produce galling wear between a tool steel ball bearing and aluminum alloy Al5083, to study the relationship between the coefficient of friction, the lump growth on the tool and the scratch morphology. Whilst the characteristic friction regimes were observed, the characteristic damage (grooves running parallel to the scratch direction) was not observed. Instead, when galling was developed on the indenter, the scratch surface morphology displayed a series of peaks and grooves perpendicular to the scratch direction. It is likely that the difference in scratch morphology observed once galling was initiated is due to the lower hardness and reduced work hardening behavior of the Al5083 alloy, compared to the high strength steels previously examined in sheet metal forming applications. The evolution of the scratch morphology has been characterized in a novel way by investigating the distribution of the longitudinal cross-section profile height along the scratch length in relation to the three-stage friction regime observed. This showed that, as the galling wear progressed, the longitudinal cross-section profile height distribution shifts towards negative values, with a corresponding shift in the distribution of material transferred to the tool shifting to the positive. This indicates that, as the amount of material adhered to the indenter increased, the depth of the grooves on the scratch surface perpendicular to the sliding direction also increased. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess intra-arch mandibular dimensional changes that may occur during mouth opening using cone beam-computed tomography (CBCT). Fifteen patients in need of any type of treatment whose execution considered a pre- and post-CBCT assessment consented and were enrolled. CBCTs were taken with the following settings: 90 kV, 8 mA, field of view (FOV) 140 by 100 mm (height and diameter), Voxel size 0.25 mm (high resolution). The pre-CBCT was executed in the maximum mandibular opening (MO), while the post-CBCT was in the maximum intercuspation (MI). A thermoplastic stent with radiopaque fiducial markers (steel ball bearings) was fabricated for each patient. Measurements were made using radiographic markers between contralateral canines and contralateral first molars and between ipsilateral canines and first molars on both sides. Paired t-tests were performed to evaluate the difference between open and closed positions on these four measurements. In the MO position were registered a significative tightening of the mandible at the canine (−0.49 mm, SD 0.54 mm; p < 0.001) and molar points (−0.81 mm, SD 0.63 mm; p < 0.001) and a significative shortening of the mandible on the right (−0.84 mm, SD 0.80 mm; p < 0.001) and left sides (−0.87 mm, SD 0.49 mm; p < 0.001). Within the study limitations, mandibular flexure determined a significant shortening and tightening between maximum intercuspation to maximum opening positions. Mandibular dimensional changes should be considered in light of other patient factors in the treatment planning of implant positioning and long-span complete arch implant-supported fixed prostheses in order to avoid technical complications. [ABSTRACT FROM AUTHOR]

Surface Mechanical Attrition Treatment (SMAT) is recognized as an effective technology for enhancing hardness and surface abrasion resistance. This study examined the influence of SMAT on the microstructure, surface roughness, hardness, and wear behavior of the AZ31 magnesium alloy. For the experiments, steel balls of different diameters - 3.2mm, 4mm, and 5.6mm - were used to perform the SMAT process, which was consistently timed at 8.5 minutes. Detailed analyses of the resultant microstructures were then conducted using tools such as a scanning electron microscope and X-ray diffraction. The hardness and wear were measured using the Vickers and the disk pin methods, respectively. It was observed that the SMAT process significantly reduced the grain size on the sample surfaces. For example, when a steel ball with a diameter of 5.6mm was utilized, the grain size was reduced from 225nm to just 96nm. The process also led to a substantial increase in hardness, with measurements rising from 65 HV to 190 HV, once again when a steel ball of 5.6mm diameter was utilized. Furthermore, the SMAT process, when executed with a tool diameter of 5.6mm, eliminated weight loss in the wear test, which had been previously recorded at 0.26mg, indicating an increase in surface abrasion resistance. An observed correlation suggested that as the tool diameters increased, the abrasion resistance of the surface improved. Abrasion was adhesive on untreated samples; on treated samples, it was ridged and scratched. However, as the tool diameter--and consequently, the surface hardness--increased, the scratches were seen to reduce gradually. [ABSTRACT FROM AUTHOR]

Polyimide-bearing retainer has been successfully used in space environment. However, the structural damage of polyimide induced by space irradiation limits its wide use. In order to further improve the atomic oxygen resistance of polyimide and comprehensively investigate the tribological mechanism of polyimide composites exposed in simulate space environment, 3-amino-polyhedral oligomeric silsesquioxane (NH2-POSS) was incorporated into a polyimide molecular chain and silica (SiO2) nanoparticles were in situ added into polyimide matrix and the combined effect of vacuum environment, and atomic oxygen (AO) on the tribological performance of polyimide was studied using bearing steel as the counterpart by a ball on disk tribometer. XPS analysis demonstrated the formation of protective layer induced by AO. The wear resistance of polyimide after modification was enhanced under AO attack. FIB-TEM confirmed that the inert protective layer of Si was formed on the counterpart during the sliding process. Mechanisms behind this are discussed based on the systematic characterization of worn surfaces of the samples and the tribofilms formed on the counterbody. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article presents the results of a study on resistance to motion in a multi-stage planetary transmission, built with lightweight structural materials such as aluminum alloy 2017, with bearing nodes featuring steel ball bearings made from X65Cr14 alloy and lubricated with molybdenum disulfide powder. Details of the planetary gear construction were presented, followed by operational performance tests. During the performance tests, the temperature of the running transmission was gradually lowered with liquid nitrogen to as low as − 190 °C. The analysis covered, among others, the power consumption of the mechanism as a function of temperature. The results were compared with the parameters of the mechanisms already working in space. The measurements were carried out to confirm the applicability of the gearing in drive systems of manipulators intended to operate in open space or under extraterrestrial conditions such as on Mars. [ABSTRACT FROM AUTHOR]

Titanium nitride has potential applications in wide range of mechanical parts, cutting tools etc., primarily due to its high wear resistance. In the present study, a novel TiN-based nanocomposite was developed with nano additives alumina (Al 2 O 3) and (Y 2 O 3), 5 wt% each; using microwave irradiation at 900 W in ambient atmosphere. In-situ microwave sintering was carried out at a temperature of 1500 °C and 5 min holding time. The sintered nanocomposites achieved a relative density of ∼93%. XRD analyses showed that the major TiN phase was retained without any significant change in its peak positions after sintering. Minor phases of Y 2 Ti 2 O 7 and Y 3 Al 5 O 12 were formed during sintering due to chemical realignment of the constituent phases, were detected which acted as crack inhibitors. Microstructural studies indicated homogeneous distribution of the additives throughout the TiN matrix. The average Vickers microhardness of the TiN nanocomposites was ∼14 GPa, while indentation crack resistance was estimated within 3.9–4.0 MPa·m1/2. Wear and friction studies (ball-on-disc) of the microwave sintered TiN nanocomposite carried out with bearing steel ball under dry (unlubricated) and under deionised water (lubricated) sliding exhibited promising tribological behaviour. The friction coefficient (COF) between the contact pair was monitored within 0.5–0.6 after 45 min of dry sliding. Wear volume of the nanocomposite was obtained between 0.013 and 0.058 mm3 after 45 min of sliding (dry). Presence of iron oxides on worn surfaces confirmed mass transfer from the steel counterbody to the nanocomposite surface. Analyses of the worn surfaces showed that the wear mechanisms were predominantly abrasive and adhesive. [Display omitted] • TiN nanocomposites with addition of Al 2 O 3 and Y 2 O 3 (5 wt% each) was processed using microwave energy • Compacts were sintered in ambient atmosphere • Sintering was accomplished with comparable mechanical and tribological properties • TiN with 5 wt% Al 2 O 3 –5 wt% Y 2 O 3 nanocomposite exhibited low dry sliding friction within 0.5–0.6 [ABSTRACT FROM AUTHOR]

Owing to its excellent wear resistance and high hardness, 440C stainless steel is widely used in the manufacturing of bearing steel balls. However, in high-speed and heavy-duty environments, bearing steel balls are prone to wear and failure, which affect their service life. This study focused on 440C stainless steel bearing balls and developed a method for preparing Ti–MoS 2 coatings and nano gradient structures on the surface of the steel balls via mechanical ball milling so as to improve their wear resistance. A detailed experimental study regarding the surface microstructure and friction performance of the processed balls was simultaneously conducted. The results demonstrated that the surface of the treated bearing steel ball formed a nano gradient structure and a 4 μm Ti–MoS 2 coating. The surface roughness of the treated sample decreased by 9.2% and the surface microhardness (831.9 ± 6.4 HV) increased by 28.93% compared to that of the untreated sample. The friction and wear experiments demonstrated that under a load of 80 N, the wear of the treated bearing steel balls decreased by 51.23% compared to that of the untreated bearing steel balls (9.94 ± 0.41) × 106 μm3. Our findings indicate that preparing Ti–MoS 2 coatings and nano gradient structures on the surface of steel balls via mechanical ball milling is an effective approach to improving the friction performance of bearing steel balls. • A new method of mechanical ball milling was proposed to simultaneously prepare coatings and gradient structures on the surface of steel balls. • Ti–MoS 2 self-lubricating coating and nano gradient structure were prepared on the surface of steel balls. • The proposed method improves the wear resistance of AISI 440C stainless steel balls. [ABSTRACT FROM AUTHOR]

Bearing elements under rolling contact fatigue (RCF) exhibit microstructural features, known as white etching bands (WEBs) and dark etching regions (DERs). The formation mechanism of these microstructural features has been questionable and therefore warranted this study to gain further understanding. Current research describes mechanistic investigations of standard AISI 52100 bearing steel balls subjected to RCF testing under tempering conditions. Subsurface analyses of RCF-tested samples at tempering conditions have indicated that the microstructural alterations are progressed with subsurface yielding and primarily dominated by thermal tempering. Furthermore, bearing balls are subjected to static load tests in order to evaluate the effect of lattice deformation. It is suggested from the comparative analyses that a complete rolling sequence with non-proportional stress history is essential for the initiation and progression of WEBs, supported by the combination of carbon flux, assisted by dislocation and thermally activated carbon diffusion. These novel findings will lead to developing a contemporary and new-fangled prognostic model applied to microstructural alterations. [ABSTRACT FROM AUTHOR]

In this paper, the effect of minimum quantity lubrication (MQL) on tool wear in the hard turning of 100Cr6 ball bearing steel has been investigated and the results are compared to those obtained through dry and wet lubrication methods. The tools used in the study include CBN and nano-CBN tools. The nano-CBN tool is a new generation of CBN tools manufactured based on nanotechnology. No research has been conducted on the impact of this tool on machining processes. The ratio of NCBN tool flank wear land to the CBN tool flank wear land in dry, wet and MQL methods were 0.18, 0.23 and 0.28, respectively. The wear of CBN tool in turning with MQL was 2.8 times greater than the wear of nano-CBN tool in dry machining. In turning with nano-CBN tool, the height of the tool flank wear with MQL was reduced by 22% and 7% concerning wet and dry methods, respectively, while these values were 51% and 24%, respectively, for the CBN tool. The CBN tool wear depends on the lubrication method but the wear of the nano-CBN tool is almost independent of the lubrication method. [ABSTRACT FROM AUTHOR]

Precision steel balls enable the bearings of machine parts to maintain their relative position, and they reduce operating time during relative movement, reduce friction force, improve efficiency and extend service life. Inspections are mainly conducted manually by eye, with classification of detected defects. Such visual inspections may cause accuracy imbalances and cost problems. For this reason, deep learning technology has been introduced into production lines. The innovation of the research presented here was to use an object-detection model to detect defects on the surface of steel balls to reduce manpower consumption and improve accuracy in detection of steel ball defects. The "You Only Look Once" algorithm (YOLOv5) was used, along with a fast-region convolutional neural network (R-CNN), finally obtaining an average recall rate of 99% and a detection accuracy rate of 93%. The results showed the YOLO algorithm to be more capable of judging good products. The contribution of this research, the efficiency of production lines can be enhanced through better detection of flaws on steel balls. The comparison showed that YOLO and Faster R-CNN are better than traditional IP detection, and the above results constitute an 80% improvement in the current detection system of the partner company. [ABSTRACT FROM AUTHOR]

Background: Regular condition monitoring of bearings has an important role in early detection of serious damages may occur on the machine. Many methods can be used to detect bearing faults, such as vibration and acoustic masurements, temperature measurements and wear analysis. Friction causes the systems temperature to rise, while the shaft-bearing system is running. Purpose: The purpose of this work, to investigate the lifetime of polymer ball bearings with regular control the vibration and temperature datas, the test rig has been designed. 6804 deep groove hybrid ball bearing consists of steel balls, polymer races has been tested. Methods: The accelerometer has been placed on the test rig for receiving and investigating vibration characteristics of the system. In addition, to determine the change of the temperature, thermocouple has been located on the test bearing housing when system working. Taken datas from the sensors have been saved on a computer with developing an algorithm environment within the experimental work. Results : Vibration results have been analyzed in time and frequency domain and associated with temperature change. The temperature-time graph and the vibration graphs which are time and frequency domain has been evaluated together. Conclusion: The results showed that accelerometer and temperature data were compatible, and temperature variation can be used to monitor bearing failure. [ABSTRACT FROM AUTHOR]

This paper presents considerations regarding skew rolling of bearing balls. The skew rolling process for producing 44.4 mm diameter balls made of 100Cr6 bearing steel is analyzed both theoretically and experimentally. Numerical simulations were performed by the finite element method using the Forge NxT simulation software. Experiments were conducted under laboratory conditions with the use of a skew rolling mill. The numerical model was validated by comparing FEM and experimental force characteristics. Thermal parameters of the rolling process and the state of strain in produced balls were analyzed. The quality of produced balls was evaluated too. The experimentally obtained balls were subjected to metallographic examination. The metallographic examination and hardness measurements of the warm-rolled balls generally showed no significant changes in the spheroidized structure of the bearing steel. The only changes with respect to microstructure and hardness were observed in the area of connectors between the balls. • The article presents warm skew rolling process of bearing steel balls. • Skew rolling was simulated in FEM and carried out in laboratory conditions. • The microstructure of the obtained products have been analyzed. • Microstructure, strain and hardness in rolled balls are non-uniform. • The system for separating balls during rolling needs improvement. [ABSTRACT FROM AUTHOR]

This work is a part of a larger research effort to better understand the combined effect of the blast wave and fragment impacts following the detonation of a shrapnel bomb. It is known that the time interval Δ t , which represents the difference in arrival time between the blast wave front and the fragment at the position of a given target object, has a significant influence on its response mode. This paper presents insights into the establishment of a laboratory scale technique to generate a combined blast loading and single or multiple projectile impacts on a target. The objective of the setup is to control the time interval Δ t to a certain extent so that the different response modes of the tested structures can be investigated. In order to reduce the complexity associated with the random nature of the shrapnel, steel ball bearings are used to simulate the projected fragments. They are embedded in a solid explosive charge, which is detonated at the entrance of an explosive driven shock tube. The experimental work demonstrates that it is possible to orient the path of a single projectile inside the tube when aiming at a target positioned at its exit. The setup guarantees the generation of a well-controlled planar blast wave characterized by its peak pressure, impulse and blast wave arrival time at the exit of the tube. The influence of the mass of the charge and the diameter of the projectile on its velocity study shows that for the same charge mass, the time interval increases with increasing projectile diameter. The experiments are numerically simulated based on an Eulerian approach using the LS-DYNA finite element software. The computational model allows to reveal details about the projectile flight characteristics inside the tube. Both the experimental and numerical data show the influence of the charge and projectile parameters on the time interval. [ABSTRACT FROM AUTHOR]

The on-line feedback control of sliding friction of metallic tribopairs lubricated by adsorbed sodium dodecyl sulfate (SDS) films was demonstrated on a customized tribosystem, in which the external electric field applied on the tribopair was modulated in feedback according to the electrical contact resistance signal. When a positive voltage was applied, the adsorption of SDS anions on the surface of tribopair was enhanced so that the boundary film was stable. When the contact resistance increased to a pre-set threshold (e.g., 6~10 Ω), which indicated the formation of a relatively complete boundary film, the external voltage was switched off for saving energy. For an aqueous solution with 160 mM SDS as the lubricant, the coefficient of friction (COF) was decreased by 24% for the 316 L plate/304 steel ball under 804 MPa by modulating the applied potential of +3.5 V. For the propylene carbonate lubricant with 5 mM SDS, the COF was decreased by 39% for the Cu plate/304 steel ball under 499 MPa and 54% for the Cu plate/bearing steel ball under 520 MPa by modulating the applied potential of +20 V. This novel approach could be effective to keep good boundary lubrication of machine components under variable work conditions by on-line sensing and actuation. [ABSTRACT FROM AUTHOR]

Herein, two types of tribocouple pairs based on polymer‐like carbon (PLC) films are designed through the in situ‐formed MXene coating. The in situ‐formed MXene coatings are synthesized via the in situ organic–inorganic chemical composite technique‐induced anionic polymers with different molecular weights (≈450 000 and ≈4 000 000, respectively). Next, the tribotesting condition is controlled in the ambient environment under different loads by bare and PLC‐coated bearing steel balls as counterbodies. During the whole sliding process, a lubricity state (friction coefficient is about 0.21 and wear rate is about 1.5 × 10−6 mm3 N−1 m−1) is realized on the self‐mated PLC system. Meanwhile, the contact surfaces are covered by graphitic 2D Ti3C2. Compared with the high‐molecular‐weight modifier system, most poly(acrylic acid)‐co‐MXenes grafted by the low‐molecular‐weight poly(acrylic acid) form far more sp2‐C phases. Moreover, active groups are potentially involved in forming a tribofilm, which enhances the overall lubricity of MXenes during sliding. This verifies the key to achieving low friction and ultralow wear based on the formation of the nanostructured sliding interface upon MXenes and provides an expanded application of solid lubricants. [ABSTRACT FROM AUTHOR]

The wear resistance of 440C bearing steel balls significantly impacts the reliability of bearings. Our method for increasing the wear resistance of steel balls combines mechanical alloying to create nanogradient structures with ZrO 2 doping on the surface of the steel balls. The results revealed that ZrO 2 formed mechanical alloying on the surface of the steel balls. Under all loads, the processed samples exhibited excellent wear resistance. Compared to untreated samples, the wear of processed samples subjected to 20, 40, and 60 N loads decreased by 28.82 %, 50.25 %, and 50.79 %, respectively. The existing literature indicates that adding ZrO 2 powder during mechanical alloying is a promising method for improving the friction performance of bearing steel balls. • The processed sample had a maximum microhardness of 803.4 HV, while the untreated sample had increased by 22.13 %. • The micro pits, nano-gradient structure, and ZrO 2 all improved the wear resistance of steel balls. • The friction experiment revealed that the processed sample had a 50.79 % lower wear rate than the unprocessed 60 N load. [ABSTRACT FROM AUTHOR]

A dicationic liquid (DIL) was synthesized and used as a base lubricant. IL-grafted graphene oxides (MGO) were manufactured as an additive to the DIL lubricant. Then, the MGO/DIL was applied as a lubricant for the surface contact between a stainless steel ball and bearing steel. The tribological performance of MGO/DIL was measured and compared to those from a monocationic liquid (MIL) based lubricant. The MGO/DIL lubricant produced better friction and wear performance at room temperature but poor wear at 100 °C. Through novel instrumentation techniques, it could be found that when DIL is exposed to air at higher temperatures, more oxygen is adsorbed into DIL, which accordingly reacts with underlying bearing steel, resulting in critical surface oxidation and wear. • The DIL [(C 1 im) 2 C 6 ][NTf 2 ] 2 lubricants and IL-grafted GO additive were synthesized • Wear and COF of steel alloy were investigated at room temperature and 100 °C • Compared to MIL, the DIL showed better thermal stability but poor friction and wear • Due to its doubly charged cation, the DIL produced severe wear at high temperature [ABSTRACT FROM AUTHOR]

Polymer composites are common materials for tribological components, even at relatively high operating temperatures. One advantage is the possibility to add low friction additives, such as PTFE, to the base material. In this paper the influence of such additives was studied, with focus on surface and sub-surface damages. The polymer composites were PPS with glass fibers (PPS-F), PPS with glass fibers and PTFE (PPS-L) and PEEK with carbon fibers, graphite and PTFE (PEEK-L). A reciprocating ball-on-disc test set-up, with ball bearing steel balls as counter material, was used with 5 N and 15 N normal load. The tests were run for 2,000 and 10,000 cycles in room temperature, 80 °C and 120 °C. PPS-F showed high friction (µ ≈ 0.4–0.5) and severe surface damage of both the polymer and the counter surface. Sub-surface cracks, detachment of fibers from the polymer and a deformed surface layer was revealed, when studied in cross section. The load and temperature had negligible effect on the friction, however a higher temperature resulted in more surface damage of the PPS-F. PPS-L and PEEK-L showed relatively low friction (µ ≈ 0.1) and superficial surface damage. XPS analysis revealed a thin tribofilm of PTFE in the wear track for PPS-L. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Working conditions such as lubrication, preload, and rotational speed have important influence on vibration and temperature rise of the spindle motor. In this study, controlled variable experiments are carried out on the silicon nitride (Si3N4) full-ceramic ball bearing and steel bearing of the same type, and the vibration signal characteristics and temperature rise of the spindle motor are tested and analysed, by changing the lubrication conditions, preloads, and rotational speeds of the spindle motor. Through the research, it is found that as the rotational speed increases, the vibration velocity of the Si3N4 full-ceramic bearing spindle motor under different preloads and lubrication conditions shows an overall increasing trend; kurtosis generally presents a downward trend and gradually flattens, indicating that although the vibration velocity increases at high speeds, the vibration signal shows a relatively stable state. As the rotational speed increases, the difference of vibration velocity under the condition of applying preload and no preload decreases, indicating that the influence of preload on the vibration of full-ceramic bearing spindle motor decreases with the increase in rotational speeds. At the same time, it is found that fr and 5fr have greater impact on the vibration of full-ceramic bearing spindle motor, where fr is the frequency of the bearing in normal operation, and 5fr is 5 times of the normal operating frequency. Lubrication conditions have little effect on the temperature rise of full-ceramic bearing spindle motor, and the temperature rise under nonlubricated conditions is even slightly lower than that under grease lubrication conditions. The research results show that the vibration velocity and temperature rise of Si3N4 full-ceramic bearing spindle motor are less than those of steel bearing with the same type, indicating that full-ceramic bearing has better performance than steel bearing under the same working conditions. [ABSTRACT FROM AUTHOR]

This study investigates the role of sliding counterbodies, which significantly affect the wear properties and friction of nanocrystalline diamond (NCD) film. The bearing steel balls exhibit a high friction coefficient of 0.12, whereas a ceramic ball of Si3N4 achieves an ultralow friction coefficient of 0.06. The evolution of different friction coefficients with different counterbodies is associated with the formation of a tribolayer at the sliding interface. The decreased friction coefficient in NCD films sliding against Si3N4 ball is likely linked to the occurrence of lubricating nanostructures, especially the silica‐like oxide compounds and graphite‐like carbon phases. The findings of this study may provide new avenues for the design and development of wear‐resistant and environment‐friendly hard carbon films. [ABSTRACT FROM AUTHOR]

In this study, the wear resistance of AISI M2 high-speed tool steel produced using direct energy deposition (DED) was investigated in detail. Wear behavior was studied under different wear loads and sliding speeds using ball-on-disk tribology tests with two different counterpart balls (bearing steel and ZrO2). The wear test results revealed that there was almost no wear damage in the M2 alloy when a bearing steel counterpart ball was used. When a ZrO2 ball was used as the counterpart, a measurable, but small, amount of wear weight loss of M2 was observed. It was found that M2 alloy fabricated by DED has excellent wear resistance, greater than fully carburized conventional steel and high wear resistance steel produced by DED. The formation of a lubricious tribo-oxide film on the worn DED M2 surface is likely the reason for its excellent wear performance. The total wear weight losses of only ~1.5 mg was observed for the M2 produced by the DED, both in the as-DEDed and heat treated states against ZrO2 balls, under the wear loading conditions of 50 N wear load, 100 mm/s sliding speed and total sliding distance of 500 m. In comparison to the other wear-resistance materials, the wear weight loss of the M2 produced by the DED was more than 6 times smaller than the fully carburized structural steel and 1.5–4 times smaller than high wear resistance steel produced by the DED. Thus, DED of the M2 alloy offers a great potential for the production of wear-resistance hard-facing of tribological components. [ABSTRACT FROM AUTHOR]

This paper presents the compressive behavior of tortoise carapace at high strain rates and its protection mechanisms under impact loading. Both experimental and numerical results are reported. Tortoise is a land-based desert-dwelling animal taxonomically classified in the order of Testudines. The carapace is the dome-shaped upper part of the tortoise shell that protects its body from predator attacks. The carapace structure is composed of four layers formed as a composite structure with a porous core. The outer surface is keratin scutes made of fibrous structural proteins. The remaining layers are bone-like materials which are dorsal cortex, cancellous interior and ventral cortex. The compressive behavior at high rate of deformation is examined using split Hopkinson pressure bar (SHPB) technique. The results shown in the stress-strain plot illustrate a strain-rate hardening effect. The impact test is conducted using a gas gun with 6.35-mm diameter steel bearing balls as projectiles. The responses of carapace sample under a range of impact velocities are investigated to analyze its protection mechanisms. The numerical model of impact test is created to obtain an insight into mechanical behaviors of the carapace structure that cannot be observed in the experiments. The strain rate dependent material model is defined based on the SHPB test results. The distributions of stress and rebound velocity are presented and discussed. [ABSTRACT FROM AUTHOR]

The recent developments in additive manufacturing (AM) are providing unprecedented opportunities in various fields, including the fabrication of advanced materials for tribological applications. The present work describes the results of an exploratory study focused on the analysis of 17-4 PH steel surfaces obtained using selective laser melting (SLM). In particular, the study includes the analysis of baseline (as-produced) and textured steel surfaces. Surface texturing comprises hexagonal prism structures (with or without dimples) arranged in a honeycomb pattern with 50 µm or 100 µm gap spacing. Starting from the minimum printing size enabled by the 3D printing platform, various textures are prepared by scaling up the characteristic dimensions of the prisms up to 500%. The obtained surface patterns are characterized (qualitatively and quantitatively) using a non-contact computerized numerical control (CNC) measuring system. The coefficient of friction (COF) was investigated using a Ball-on-Disk configuration using bearing steel balls as counterparts. For a fixed sliding speed, different contact loads and sliding radii were considered, while the tests were carried out in either dry or lubricant-impregnated conditions. The results of wear tests in both dry and lubricated conditions indicated that the baseline samples are provided with lower COF compared to the textured ones. For the latter, neither the gap spacing nor the presence of dimples led to significant variations in the COF. However, in lubricated conditions, the values of the COF for baseline and textured surfaces were closer and much smaller. In particular, the results provide clear indications regarding reducing the gap between prisms, which had a beneficial effect on the COF in lubricated conditions. Similarly, sensitivity to dimples was quite remarkable, with a reduction in the COF of about 30% when the larger gap spacing between the prisms was used. [ABSTRACT FROM AUTHOR]

If a smooth ball is dropped vertically without spin on a smooth horizontal surface then one might expect the ball to bounce vertically without spin. If it does not then the centre of mass of the ball does not coincide with its geometric centre. An experiment is described where a billiard ball and a superball are deliberately biassed by adding a small steel ball on one side. The results agree well with theoretical calculations. [ABSTRACT FROM AUTHOR]

Direct simple shear (DSS) testing allows observation of load-deformation response under rotation of the major principal stress plane, which is descriptive of many actual field problems. While the simplicity of the test configuration makes its use popular in research and industry, key uncertainties still remain regarding the interpretation of the laboratory data. This study uses laboratory validated discrete element method (DEM) models to examine the stress transmission in laminar-type direct simple shear devices under drained constant effective stress conditions. The DEM models (comprised of spheres) closely replicate physical specimens of precision chrome steel ball bearings for which the properties (e.g., shape, surface friction, and stiffness) were measured directly. The DEM models were also validated using experimental tests, so that conclusions regarding the system response can be derived with confidence from the available DEM data. The testing program included both loose and dense specimens, allowing for a comparison of the influence of density on stress state which has not been examined in previous simple shear DEM studies. Differences were observed between vertical effective stresses and shear stresses derived from boundary measurements (as commonly carried out in experimental programs) and those derived from force measurements within the DEM specimens. The failure state of the material in simple shear was also examined through Mohr's circles of stress. The evolution of stresses on both the horizontally and vertically oriented planes were considered so that established methods of direct simple shear interpretation could be critically assessed. For the loose specimens, the angle of shearing resistance can be confidently estimated considering the maximum shear stress acting on the horizontal plane, which is easily inferred from measurements of the shear force during the physical test. This was true considering both internal and boundary calculated stresses. This approach, however, is inaccurate for the dense specimens. Analysis of the particle-scale kinematics of the response illustrates that the deformation field within the central portion of the specimen is in simple shear, although the magnitude of this shearing was significantly larger than what was measured on the boundary. This study and the conclusions derived focus on smooth spherical particle specimens; the objective was to examine the stress distribution within DSS devices and the implications for test interpretation using DEM models that more closely matched the physical laboratory specimens tested than in previous studies. When considered alongside the existing studies, the findings show that there is no broad conclusion that can be applied for all materials and all conditions in simple shear and that interpretation should be carefully tied to the physical conditions simulated. [ABSTRACT FROM AUTHOR]

This study explored 440 C steel ball wear resistance via mechanical ball milling with Al 2 O 3 powder. We used a customized grinding jar to compare heat-treated, untreated, Al 2 O 3 -treated, and Al 2 O 3 + distilled water-treated samples. We assessed wear resistance, residual stress, microhardness, and surface roughness. Results revealed that the combination of distilled water and Al 2 O 3 powder induced nanostructured stacking faults, increased dislocation density, and grain refinement. Treated samples had a > 200 µm thick strengthened layer, − 355 MPa residual stress, and max microhardness of 776.6 HV. These samples showed superior wear resistance, reduced wear volume, and lower friction. This suggests that Al 2 O 3 powder and distilled water in mechanical ball milling enhance ball mechanical part wear resistance, offering industrial potential. [ABSTRACT FROM AUTHOR]

In this work, we designed three series of tribo-couples based on amorphous carbon films including GLC, DLC and PLC that were modified by graphene quantum dots (GQDs). The tribo-testing environment was controlled at harsh conditions (like heavy load and high speed) in dry nitrogen atmosphere using bare and film-coated bearing steel balls as counterbodies, respectively. Through the tribochemical interactions, the self-mated DLC system obtained a surperlubricity state (μ = 0.01). During the whole sliding, the contact surface of the upper counterfacing ball was covered by 2D-layered carbon and graphitic lubricants induced via structural transformation of GQDs. Meanwhile, the tribofilm of the disc wear track was composed of a silica-like SiO x boundary layer and a multicomponent mixed-layer induced by tribochemistry. Compared to the self-mated DLC system, the structural boundary enriched with SiO x compounds was not formed at the bottom region of the tribofilm for the bare steel system; meanwhile, the disc wear track was covered by a thicker tribofilm containing plenty of degraded GQDs. This inferred the fact that the formation of a nanostructured sliding interface was the key to realize superlubricity. These discoveries successfully afforded a lubrication mechanism of GQDs for solid lubricant in applications of engineering and industry. Image 1 • Graphene-quantum-dots lubricants with effective friction-reducing effects are achieved. • The lubricity depends strongly on the tribo-couple materials and surface strucutre. • The nanostructured tribofilms formed on the contacts govern the superlubricity mechanisms. [ABSTRACT FROM AUTHOR]

Purpose: Bearings in electric machines often work in high speed, light load and vibration load conditions. The purpose of this paper is to find a new fatigue damage accumulation rating life model of ball bearings, which is expected for calculating fatigue life of ball bearings more accurately under vibration load, especially in high speed and light load conditions. Design/methodology/approach: A new fatigue damage accumulation rating life model of ball bearings considering time-varying vibration load is proposed. Vibration equations of rotor-bearing system are constructed and solved by Runge–Kutta method. The modified rating life and modified reference rating life model under vibration load is also proposed. Contrast of the three fatigue life models and the influence of dynamic balance level, rotating speed, preload of ball bearings on bearing's fatigue life are analyzed. Findings: To calculate fatigue rating life of ball bearings more accurately under vibration load, especially in high speed and light load conditions, the fatigue damage accumulation rating life model should be considered. The optimum preload has an obvious influence on fatigue rating life. Originality/value: This paper used analytical method and model that is helpful for design of steel ball bearing in high speed, light load and vibration load conditions. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2019-0180/ [ABSTRACT FROM AUTHOR]

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