Hertzian Contact Stress Research Articles

Quantitative analysis and validation using computational approach for hollow spherical roller bearing 22212E

A bearing is a part of the machine that lowers friction between moving parts by limiting relative motion to only the desired motion. Bearing debility is affected by a several factors, also the roller–raceway interfaces are the most significantly stressed areas in a bearing, minimizing the Hertz contact stresses there has been a main objective. The analytical and finite element approaches have been used to evaluate the deformation, contact stress and contact pressure of spherical roller bearings 22212E. It has been observed that the acquired results employing the theoretical and FE Analysis methods have quite a 9 percent variation. Based on results, confirming the FEA for solid spherical bearing with a theoretical approach using the same operating parameters. Furthermore, the finite element approach has been employed to analyse how the hollow spherical rolling element enhanced the bearing performance. In ANSYS, multiple hollowness percentages ranging from 0% to 90% of the external diameter of the spherical roller were analysed in order to determine the optimal hollowness for bearing service life. It has been discovered that bearings with a hollowness of roughly 62 percent have the lowest contact stress, which extends the bearing's fatigue life.

Genesis of Superlow Friction in Strengthening Si-DLC/PLC Nanostructured Multilayer Films for Robust Superlubricity at Ultrahigh Contact Stress.

Diamond-like carbon (DLC) films have significant potential to provide solutions for the friction reduction and the lubricity problem of mechanical moving friction pairs. However, the realization of excellent lubrication or even superlubricity and long lifetime under heavy loading conditions is still a great challenge, which is crucial for the applications of DLC in harsh environments. Here, we construct a group of property-strengthening Si-DLC/PLC multilayer films that could withstand ultrahigh contact stresses and achieve robust superlubricity. Under a peak Hertz contact stress of up to 2.37 GPa, the setup of a bilayer thickness of 324 nm enables the multilayered film (an overall film thickness of 1.53 μm) to achieve a superlow coefficient of friction toward 0.001 and an ultralow wear rate of 3.13 × 10-9 mm3/Nm. An alternating load reciprocating friction test emphasizes that this strengthening nanostructured Si-DLC/PLC multilayer possesses a kind of load self-adaptation because of its in situ nanoclustering transformation and local ordering of sp2-C phases at the sliding interface. The genesis of self-adaptation to the applied load is evaluated comprehensively to reveal its strengthening and toughening structural characteristics and robustness of the near-zero friction and wear features. The findings provide a significant design criterion for carbon-based solid lubricants applicable to harsh loading environments.

Tribological behaviour of a multilayer CrN/DLC coating obtained using PVD-MS

Diamond-like Carbon (DLC) coatings are used as protective layers for steel components due to their hardness, chemical inertia and interesting tribological properties. Reducing wear and friction coefficient is of great importance for industries today in order to increase energy efficiency and reduce harmful emissions to the environment. In this paper, a multilayer CrN/DLC coating is analysed. It was deposited using a commercial Plasma Enhanced Magnetron Sputtering over nitrided and not nitrided mild-alloy steel AISI 4140, produced for the first time in Argentina, at the firm Coating.Tech by Flubetech-Tantal. The base of the coating is an anchor layer made of CrN and the top layer is a chromium-dopped hydrogenated amorphous carbon (a-C:H:Cr), which provides excellent tribological properties. Wear tests were carried out in a Pin-on-Disk apparatus, using an Al2O3 ball as counterpart, with Hertzian contact stress from 1370 up to 1460 MPa. The friction coefficient was μ ∼ 0.1, which is 80% less than the untreated steel and the wear volume loss was reduced several times. The adhesion was evaluated by means of Scratch Test, where major improvement was noticed in the samples which were nitrided as pre-treatment, increasing critical load from 25 N up to 65 N.

Computational Analysis of Contact Stresses In Involute Spur Gears

The present paper investigates computational analysis of the contact stresses involved in an involute gear system using ANSYS simulation software. Gearing is one of the most critical components in mechanical power transmission systems. The computational simulation of contact stresses of two cylinders is carried out to validate the methodology with available analytical method, Hertz contact stress equation, which are originally derived for contact between two cylinders. The simulation of contact problems with ANSYS is carried out with the stiffness relationship between the two contact areas is usually established through a contact element, spring type is placed between the two contacting areas. The results of the two dimensional FEM analyses using ANSYS, a FEM solver software are presented. The results simulated are in agree with the theoretical values calculated using Hertz contact stress equation

Macro-superlubric triboelectric nanogenerator based on tribovoltaic effect

<h2>Summary</h2> Reducing the coefficient of friction (COF) and wear rate is significant for triboelectric nanogenerators (TENGs). Here, we devised a new macroscale superlubric triboelectric nanogenerator (SL-TENG) that can withstand high-contact stress with ultralow COF (<0.01) and ultralow wear rate based on a hydrogenated diamond-like carbon (DLC) film from the tribological perspective. Specifically, the SL-TENG produced an output with the peak short-circuit current of approximately 60 nA and a power density of up to 5.815 W/m² during the friction of <i>DLC</i> versus <i>steel ball</i> with a Hertz contact stress of 1.37 GPa. Moreover, first-principle calculations demonstrate that the ultralow friction on DLC is mainly due to the hydrogen-terminated surface. The SL-TENG can generate direct current (DC) output caused by tribovoltaic effect and can light up several light-emitting diodes (LEDs) without rectification. Online superlubric friction monitoring and early warning can be realized, owing to the close correspondence between tribology and triboelectricity.

Interaction of anti‐wear additiveTCPwith advanced bearing steels

AbstractThe quest for high‐performance energy efficient aircraft turbine engines has led to the development of a number of high‐performance rolling element bearing materials and engine lubricants with the aim of providing superior mechanical component durability. The heat treatments/surface treatments used to achieve the desired physical and mechanical properties for these newer alloys can result in altered surface chemistry from currently used materials. Surface chemistry plays an important role during lubricant‐bearing material interactions and the formation of beneficial tribological films during component operation. The objective of this study was to analyse the tribo‐films formed on bearing surfaces and investigate the interaction of lubricant additives, specifically the phosphorus‐based anti‐wear additive tricresyl phosphate (TCP), with different bearing materials under relevant bearing operating conditions. Bearing tests were conducted on 208‐size (40 mm bore) angular contact bearings at 127°C and 154°C using gas turbine engine lubricants conforming to MIL‐PRF‐23699G at maximum Hertzian contact stresses of 3.1 GPa and 3.55 GPa. Bearing materials evaluated included AISI M50, M50NiL, nitrided M50NiL (N) and three variants of Pyrowear 675 with silicon nitride rolling elements. Tribo‐films were analysed using Energy dispersive X‐ray spectroscopy and Auger Electron spectroscopy. Results indicate that phosphorus‐rich anti‐wear tribo‐films form on all of the bearing materials studied. The applied thrust load and heat treatment had a significant effect on tribo‐film thickness. The study also suggests that current gas turbine engine lubricants formulated with TCP should form beneficial tribo‐films that enhance bearing fatigue life and performance.

Hertzian stress analysis of metal and 3D printing materials

In this paper proposed the hertzian contact stress analysis of two components which were made of steel and Nylon 6. This material can be used for 3D printing purposes. In novelty, the authors want to observe the contact pressure between those two materials by considering as torque transmission elements, Gear and Pinion. It was observed that highest contact stress was on Nylon materials when it was in contact with steel and validated through computational techniques.

Tribological behaviors of MoAlB ceramic in artificial seawater

In this work, we systematically studied the tribological behaviors of MoAlB ceramic under different counterpart materials (Al2O3, Si3N4, SiC and 316L) in artificial seawater. MoAlB ceramic exhibits high wear rates when sliding against Al2O3 and Si3N4 because of the high Hertzian contact stress, but a thin layer of Al(OH)3 gel film contributes to a low friction coefficient of 0.19 for MoAlB/Al2O3 tribopair; when sliding against 316L, the large hardness difference and severe adhesion of 316L lead to a highest friction coefficient but a low wear rate for MoAlB. When MoAlB ceramic slides against SiC, a lubricating hydrated silica tribofilm makes MoAlB obtain the best tribological performance with a friction coefficient of 0.12 and a wear rate of 6.63 × 10−7 mm3·N−1·m−1.

Experimental and numerical evaluation of the contact fatigue resistance of AlCrN, FexN and AlCrN/FexN coatings on AISI 4140 steel

An experimental-numerical study of the contact fatigue resistance of AlCrN coatings formed on an AISI 4140 steel was performed. Three different coatings were formed: a coating of aluminum chrome nitrides (AlCrN) by a physical vapor deposition process (PVD) with a thickness of 2.2 ± 0.3 μm, a layer of iron nitrides (Fe x N) by a gas nitriding process with a compound layer of 10 ± 1 and an underlying diffusion zone of 65 ± 4 μm and finally a duplex system of AlCrN/Fe x N with a thickness of 3.0 ± 0.2 μm of AlCrN, a compound layer with a thickness of 2.5 ± 0.3 μm and 16 ± 3 μm of the diffusion zone. Contact fatigue tests were performed on a MTS Acumen electrodynamic test system, by applying cyclic loading to each of the coatings using a sphere to generate Hertzian contact stresses. The contact fatigue test methodology consisted of two main stages. First, the critical load of each formed system was obtained by means of the application of monotonic loads, where the monotonic load value in which the first circular cracks on the coating surface were observed was set as the critical load. The critical loads of the three coatings were: Fe x N: 800 N, AlCrN: 1000 N and AlCrN/ Fe x N: 1100 N. Second, fatigue conditions were performed up to 100,000 cycles using subcritical loads with a frequency of 5 Hz. Cohesive damage was observed in the samples containing iron nitrides, whilst delamination was caused on the AlCrN single layer coating. A numerical model based on the finite element method was developed to evaluate the stress field generated in the systems by cyclic contact loading. The thinner thickness and the abrupt transition of mechanical properties from the coating to substrate caused the maximum principal stress to be located within the contact zone in the AlCrN single layer coating. Results showed better resistance to contact fatigue in the AlCrN/Fe x N duplex system because of the presence of the intermediate layer of iron nitrides. • AlCrN/Fe x N coatings were evaluated by standing contact fatigue. • Influence of nitride layer in the duplex system under contact fatigue was analyzed. • Failure mechanism was less severe in the duplex system under contact loading. • Contact stresses were related with failure mechanisms observed in the coatings. • Nitride layer in the duplex system avoid the adhesive failure of coating.

Theoretical research on the wear characteristics of rotors in a twin-screw compressor

Thanks to the development and application of coating technology and polymer rotor material, it is an inevitable trend to eliminate synchronous gear for water-injected and dry twin-screw compressors, especially running at a high speed, due to much power consumed by synchronous gears. However, it is not economical and reliable to rely only on coating or rotor material to enhance the wear resistance of rotor. This paper attempts to lighten the rotor wear in twin-screw compressors from the angle of setting driving belt. To achieve this goal, the contact analysis is carried out in this paper, taking the rotor profile of a developed water-lubricated twin-screw air compressor as an example. By the contact analysis, equivalent curvature radius, Hertz contact stress, sliding distance, the value of PH S, and the minimum film thickness of each mesh point on different tooth curve are calculated and discussed. The product of the Hertz contact stress and total sliding distance, PH S, and minimum film thickness are chosen as the evaluation indexes to estimate the wear resistance of all tooth curves. By comparing these indexes of each tooth curve, some suggestions about setting the driving belt are proposed.

A novel tooth tip relief method for reducing micro-pitting of spur gears

Micro-pitting is a common fatigue failure mode of spur gears. To reduce it, this paper proposes a novel tooth tip relief method. Gear meshing simulation is firstly performed considering the actual contact path, showing that there are four Hertz contact stress peaks in the transition areas of the tooth flank. Equations are then developed for the novel tooth tip relief method: one focuses on the smooth transition between the involute profile and the tip relief region, the other on the smooth transition between the tip relief region and the tooth tip. The results of curvature radius and Hertz contact stress show that the proposed novel method can effectively reduce the Hertz contact stress peaks, which indicates this tip relief method could benefit for reducing the micro-pitting. Finally, both wear simulations and bench tests are conducted, verifying the effectiveness of the proposed method for reducing the micro-pitting of spur gears.

Effect of Artificial Aging on Mechanical and Tribological Properties of CAD/CAM Composite Materials Used in Dentistry.

With easy-to-process 3D printing materials and fast production, the quality of dental services can be improved. In the conventional procedure, the dentist makes temporary crowns directly in the patient’s mouth, e.g., from the most commonly used bis-acrylic composites. Temporary crowns made directly in the office without the use of CAD/CAM are often of inferior quality, which directly results in impaired hygiene, poorer masticatory mechanics, greater deposition of plaque, calculus and sediment, and may adversely affect periodontal and gum health. The mechanical strength, resistance to aging and abrasion of 3D printing materials are higher than those of the soft materials used in conventional methods. This translates into durability. The patient leaves the surgery with a restoration of higher utility quality compared to the conventional method. The objective of the paper was to determine the influence of aging in artificial saliva of AM (additive manufacturing) orthodontic composites on their functional properties. For the purpose of the study, fillings well-known worldwide were selected. These were traditional UV-curable resins (M I, M II, M III, M V) and a hybrid material based on a UV-curable resin (M VI). Samples were stored in artificial saliva at 37 ± 1 °C in a thermal chamber for 6 months. Indentation hardness, frictional tests and sliding wear measurements were conducted. A comparison between various materials was made. Descriptive statistics, degradation coefficients, H2E, Archard wear and specific wear rate were calculated. The Weibull statistical test for indentation hardness was performed and Hertzian contact stresses for the frictional association were calculated for unaged (M I, M II, M III, M V, M VI) and aged (M I AS, M II AS, M III AS, M V AS, M VI AS) samples. M I exhibited the lowest average hardness among the unaged materials, while M III AS had the lowest average hardness among the aged materials. Comparably low hardness was demonstrated by the M I AS material. The coefficient of friction values for the aged samples were found to be higher. The lowest wear value was demonstrated by the M I material. The wear resistance of most of the tested materials deteriorated after aging. The M VI AS material had the highest increase in wear. According to the results provided, not only the chemical composition and structure, but also aging have a great impact on the indentation hardness and wear resistance of the tested orthodontic materials.

Synergistic effects of a combined surface modification technology on rolling contact fatigue behaviors of 20CrMoH steel under different contact stresses

Ultrasonic surface rolling (USR), carburizing and the combined (Carburizing + USR) strengthening method were applied on the 20CrMoH steel, and the rolling contact fatigue (RCF) mechanisms of 20CrMoH steel subjected to different strengthening methods are analyzed. Results indicated that the combined strengthening method effectively increased the surface hardness value from 370 HV0.2 to 900 HV0.2, produced the highest residual compressive stress (RCS) value of −920 MPa and markedly reduced the surface roughness value to 0.48 μm. Under the Hertz contact stress of 2.02 GPa, the RCF life of the combined treated samples increased by 100% compared to the carburized samples, and the delamination mainly occurred. Surface roughness and RCS are important factors for anti-RCF failure.

Tribological Properties of SiO2@Cu and SiO2@MoS2 Core–Shell Microspheres as Lubricant Additives

Herein, core–shell structural SiO2@Cu and SiO2@MoS2 microspheres were prepared using SiO2 as hard core, Cu and MoS2 as shell. As lubricant additives were introduced into base oil (PAO 40), their friction reduction and wear resistance were investigated in detail. Comparing with onefold additive (SiO2, Cu and MoS2), such core–shell structural additives can improve the tribological behaviors at the Hertz contact stress range of 1.26–2.72 GPa (SiO2@Cu reduces the friction and wear up to 32.47% and 67.86% at 2.72 GPa, respectively). Besides, the tribological properties of SiO2@Cu microspheres are superior to that of SiO2@MoS2 (the wear volume was reduced by 48.45% at 2.72 GPa). The excellent tribological behaviors of SiO2@Cu microspheres can be ascribed to its structural advantage, the synergistic effect of hard SiO2 core and Cu shell. The rolling effect of SiO2, easy-shearing and self-repairing of Cu shell offer a synergistic lubrication function and form a dense protection film, thereby contributing to the optimal lubrication performance.

Under-stoichiometric cementite in decomposing binary Fe-C pearlite exposed to rolling contact fatigue

In this study, we investigate the fundamentals of deformation-driven cementite decomposition during rolling contact fatigue in a binary Fe-0.74C (wt.%) steel with pearlitic microstructure. To reveal the involved nano-scale mechanisms, we apply transmission electron microscopy and atom probe tomography, as well as the combination of both techniques on the same probe volume for correlative structural and chemical analysis. After ~32,500 individual ball contacts under a nominal Hertzian contact stress of ~1,250 MPa, cementite lamellae are consistently depleted in carbon (C) down to ~20 at.%, which is a reduction of 20% in comparison to the original stoichiometric composition of 25 at.% before deformation. By electron diffraction on atom probe tip volumes, we show that this under-stoichiometric cementite still maintains its crystal structure. The potential effect of temperature increase during rolling contact fatigue on cementite decomposition is addressed by carrying out annealing experiments at 150°C and 250°C for 30 minutes after rolling contact fatigue. Our results show that slip transmission across cementite lamellae is primarily responsible for the observed C-depletion in cementite. We quantitatively discuss slip transmission from ferrite to cementite using slip trace analysis and correlate the amount of slip activity with the observed C-depletion. In this way, we explain the formation of under-stoichiometric cementite by combined slip transmission and solute drag by dislocations, where C is transported out of cementite by dislocation gliding through cementite lamellae. Only afterward, cementite decomposition in terms of phase dissolution is suggested to occur by the dislocation-shuffle mechanism.

캠 랙 피니언 시스템의 강도설계

The cam rack pinion (CRP) system takes the traditional rack and pinion concept and advances it by replacing the pinion teeth with bearing supported rollers that engage a trochoid rack tooth profile. The bearing supported rollers eliminate the sliding friction of the conventional rack and pinion with smooth rolling friction that yields a 99% efficient rotary to the linear motion conversion. In this study, the fatigue failure life of a CRP system was investigated. First, we investigated the difference in rack tooth profiles by changing the profile shift coefficient of CRP systems. Next, the Hertz contact stresses and tooth root bending stresses were analyzed by varying the profile shift coefficient to determine the tooth fatigue characteristics. It was found that the variation in the contact force with increasing the profile shift coefficient was insignificant, but the Hertz contact and tooth root bending stresses decreased significantly.

Interaction between a cylinder and a partially saturated soil for compaction analysis

Compaction is probably the industrial process more intensively used in road construction. The current compaction practice is based on the useful methodology proposed by Proctor (1933). This methodology intends to reproduce field compaction in the laboratory by applying a controlled mechanical energy to the soil and relating the dry density with the water content. However, recent developments in soil compaction analysis in the laboratory and field seek a better understanding of the link between the mechanical stresses applied to the soil and the strains it undergoes. This requirement needs analyzing the stresses applied to the soil by the compaction machine, the distribution of stresses within the soil layer undergoing compaction, and the behavior of the partially saturated soil. This article explores the feasibility of using a series of simplified analytical equations to model compaction within a mechanical framework. The proposed model focuses on the compaction produced by a cylinder applying a static load. The methodology combines the Hertz contact stress theory with the Fröhlich stress distribution and the Barcelona Basic Model for partially saturated soils. The results of the proposed analytical model successfully agree with the experimental observations obtained using a geotechnical centrifuge model and confirming its potential use for compaction control and monitoring.

Na2CO3 and graphene nanocomposites toward efficient lubrication

Lubrication by graphene from nanoscale to macroscale has attracted increasing interest in recent years. However, the graphene can only withstand load of 2 N (corresponds to Hertzian contact stress of 0.41 GPa) during sliding. In this work, a composite of graphene and sodium carbonate coating shows an improved load-carrying capability during lubricated contacts. Compared to the pure graphene deposited coating, the composite can reduce the friction from 0.6 to 0.16 and wear by one order of magnitude at 1.29 GPa, and can provide an effective lubrication even at the high load of 40 N (corresponds to maximum Hertzian contact stress of 2.06 GPa). The improved lubricating property by the composite of sodium carbonate and graphene results from the stronger adhesion of the composite on the steel surface and the sliding induced soft tribofilm formed at the rubbing interface. Interface observation indicates a high sp2 fraction of carbon at the top of the tribofilm which contributes to the easy slippery. This study provides a new approach to widen the applications of graphene to lubricated contacts under heavier loads.

Tribo-mechanism of amorphous carbon films under corrosion solution and various mechanical loads

Diamond-like carbon films (DLC) as a prominent surface protection coating are used to enhance the tribological performance of engineering components due to their low coefficient of friction (COF), high wear resistance and excellent chemical stability. In recent years, researchers have separately studied the environment-dependent and load-dependent tribological behaviors of DLC films. However, there is few studies about the influence of corrosive media on the load-dependent tribological behaviors of DLC films. In this paper, we explained the tribo-mechanism of chromium doped DLC film (Cr-DLC) in hydrochloric acid (HCl) by combing the effect of load-dependent. For comparison, tribological behaviors of Cr-DLC films in ambient air and distilled water environment were also investigated. It is found that the coefficient of friction of Cr-DLC film complies with the Hertzian elastic contact model in HCl solution. In other words, the COF decreases with the increase of normal contact load except 2 N. The Cr-DLC film shows the highest wear resistance with wear rate of 1.79 × 10−7 mm3/Nm at 5 N. The main wear mechanism at 2 N and 5 N is governed by the formation of a graphite-like transfer film and tribochemical products on friction interfaces; Whereas the wear mechanism for 7 N and 10 N contact load is attributed to the superimposed effect of the high Hertzian contact stress and the corrosion function of chloride ion. The insights acquired from this study can be used to the design of high-performance of DLC coated tribo-systems in corrosive environment.

A study on the rotor profile and internal clearances of the gerotor pump used in lubricating system of gas turbine engine

Gerotor pump is widely used in lubrication systems of a gas turbine engine where compactness and reliability is of key importance. In this work, the characteristic of the pump is studied for its application in the lubrication system. The rotor profile geometry of the Gerotor pump and its effect on the flow characteristics such as specific flow rate and flow irregularities is studied. The effect of the rotor geometry on the wear characteristics have also been taken into account by considering Hertz contact stress and the relative sliding velocity between the rotors. A Gerotor pump having fixed geometrical parameters designed based on mathematical 1D model using MatLab and AMESim software used for the profile generation and studying the theoretical flow characteristics. This work is further extended by studying the various internal leakages of the pump. The predicted flow rates obtained from Amesim software were then compared with the experimental results and found close match within 5% deviation. Hence, this methodology can be used to estimate performance and wear parameters. This study can assist pump designers to select geometrical parameters and internal clearances of gerotor pump as per their requirements.