Maximum Hertz Stress Research Articles

5228 無潤滑条件下におけるWCサーメット溶射皮膜の耐久性 : 母材硬さと下地加工の影響(S66-1 サステイナブルトライボロジー(1),S66 サステイナブルトライボロジー)

Using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating under unlubricated condition. By means of the high energy type flame spraying (Hi-HVOF) method, the coating of about 110μm in thickness was formed onto the axially ground, blasted and circumferentially ground roller specimens made of a thermally refined carbon steel or a carburized and hardened steel. The WC cermet coated roller finished to a mirror-like condition with a roughness of 0.1μmRz was mated with the carburized and hardened steel roller without coating ground to a roughness of 0.1μm〜8μmRz, and a maximum Hertzian stress of P_H=1.2GPa was applied in line contact. In the case of the thermally refined steel substrate, the life to flaking became short independent of the substrate surface finish. On the other hand, the carburized hardened steel substrate roller showed a higher durability. The effect of substrate material on the durability of thermally sprayed coating was discussed by the elastic-plastic analysis of the subsurface layer.

Effects of substrate surface finish and substrate material on durability of thermally sprayed WC cermet coating in rolling with sliding contact

In this study, using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling with sliding contact conditions. The coating was formed onto the axially ground, blasted and circumferentially ground roller specimens made of a thermally refined carbon steel or an induction hardened carbon steel by means of the high energy type flame spraying (Hi-HVOF) method. The WC cermet coated roller finished to a mirror-like condition was mated with the carburized steel roller without coating having a surface roughness of Ry=3.0∼5.0 μm. In the experiments, a maximum Hertzian stress of P H=0.6 or 0.8 GPa was applied for the thermally refined carbon steel roller and P H=1.4 GPa was applied for the induction hardened carbon steel roller in line contact condition. As a result, it was found that in the case of induction hardened steel substrate, the coated roller generally exhibits a long life without any serious damage and the surface durability is hardly affected by the substrate surface finish, while in the case of thermally refined steel substrate, the durability of coated roller is lowered and the life to flaking is very short particularly when the substrate surface is circumferentially ground and the mating surface is rough. The surface durability of coated roller was also compared with the durability of steel roller without coating. Finally, in order to discuss the durability of coated roller, the elastic-plastic behavior of the subsurface layer under repeated rolling with sliding contact was analyzed using a finite element method (FEM).

Tribological behaviour of hot rolling rolls

The study of wear mechanisms represents a very important task for the development of roll materials, with improved hot tribological properties. In the present paper the wear behaviour of different materials, i.e., high alloy steels (high speed steels (HSS)) and cast irons (high chromium irons (HiCr) and indefinite chill irons (IC)), produced by centrifugal casting, has been comparatively evaluated by means of a rolling sliding hot wear test. A disc specimen of C40 plain carbon steel, induction heated up to 700 °C, is allowed to rotate against a high alloy steel/iron at 200 rpm, corresponding to a slip rate of 28%, for a total period of time comprised between 1 and 3 h. A maximum contact hertzian stress of 300 MPa was imposed. The wear rates have been evaluated by weight measurements of the specimen, before and after each test period. The surface roughness was also determined as representative for the roll profile retention during service. The friction was continuously monitored. The wear mechanism is given by the combination of abrasion and oxidation. High speed steels show remarkable lower wear rates than high chromium and indefinite chill irons, because of their higher hot hardness. The retention of high hardness at elevated temperature is very important to reduce abrasive wear and also to support the protective oxide layer which develops on the surface of the roll material. As a general rule the roughness at the end of test tends to increase with increasing wear rate, as demonstrated by the relatively soft indefinite chill iron. However, the oxidation resistance also influences the final roughness, higher roughness values being observed for poorly oxidized materials. A simplified model explaining this experimental evidence is proposed.

Boundary Lubrication RCF Performance of 4 cSt Gas Turbine Engine Oils at 204 °C

The rolling contact fatigue (RCF) and wear performance of three qualified formulations of MIL-L-7808K (4 cSt at 100 °C) were evaluated using AISI VIM-VAR M50 steel. The RCF tester differentiated the fatigue life and wear performance of gas turbine engine lubricants in boundary lubrication regime. Tests were conducted using a ball-on-rod type RCF tester at a maximum Hertzian stress of 4.8 GPa and temperature of 204 °C. Although all the three lubricants meet the military specification, the RCF results suggest that life and wear in the boundary lubrication regime are significantly affected by the formulation. Changes in physical and chemical properties of post test lubricants such as viscosity, acid number and additive concentration were minimal. However, the lowest Fe concentration and COBRA reading, which is a measure of the electrical property of the lubricant, correlated with the highest RCF life and lowest wear.

軸受鋼ローラの転がり疲れ : TEHL理論による検討(OS13-2 一般講演(II))

Using a two-roller testing machine, the rolling contact fatigue life of bearing steel rollers with mirror-like smooth surfaces was examined. A pair of rollers were driven under the rolling with sliding condition of s=-3.2%, and a maximum Hertzian stress in the range of PH=3.0GPa〜4.0GPa was applied in point contact condition. As lubricant, a low viscosity synthetic traction oil with viscosity grade of ISO VG 32 was used, and the test results were compared with those obtained using a low viscosity mineral oil with almost the same viscosity grade. Consequently, the fatigue life with a low viscosity traction oil was shorter than that with a low viscosity mineral oil, and this tendency appeared more distinctly under higher stress conditions above PH=3.4GPa. Based on the numerical calculation results of the thermal EHL, the authors discuss the mechanism which causes such a difference in the fatigue life.

132 転がり-滑り接触下における WC サーメット溶射皮膜の耐久性に及ぼす下地処理の影響

Using a two-roller testing machine, the authors have examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling or rolling with sliding contact conditions. In the present investigation, the coating of 20 to 200μm in thickness was formed onto the blasted or ground roller specimens made of a thermally refined carbon steel, an induction hardened carbon steel and a carburized alloy steel by means of the high energy type flame spraying (Hi-HVOF) as well as the conventional high velocity oxygen-fuel flame spraying (HVOF). The WC cermet coated roller finished to a mirror-like condition was mated with the carburized steel roller without coating and a maximum Hertzian stress of PH=1.2 or 1.4GPa was applied in line contact. As a result, it was found that the coating on the blasted substrate roller generally shows a higher durability compared with that on the ground substrate roller and this difference appears more distinctly as the coating thickness decreases. In addition, it was also confirmed that the life to flaking of coated roller is prolonged as the hardness of substrate is raised and the coating thickness increases.

Effects of coating thickness and slip ratio on durability of thermally sprayed WC cermet coating in rolling/sliding contact

Using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC–Cr–Ni cermet coating in lubricated rolling or rolling with sliding contact conditions. The coating was formed onto the roller specimen made of an induction hardened carbon steel or a thermally refined carbon steel by high velocity oxy-fuel flame spraying (HVOF). In the experiments, the WC cermet coated roller was mated with the carburized steel roller without coating and a maximum Hertzian stress of P H=1.2 or 1.4 GPa was applied in line contact. First, it was recognized that the life-to-flaking has a tendency to increase as the thickness of coating increases. Secondly, it was shown that the occurrence of flaking depends on the rolling/sliding conditions. Finally, based on the results of elastic–plastic analysis of subsurface layer, the authors discussed the effects of the coating thickness and the slip ratio on the durability of coated roller.

Rolling Contact Fatigue (RCF) resistance of Austempered Ductile Iron (ADI)

The present work reports on the Rolling Contact Fatigue (RCF) resistance of Austempered Ductile Iron (ADI) as evaluated by using a ball–rod rolling contact fatigue tester. The tests were carried out until a spall was detected with a load ratio p 0/ k k=6, where p 0 is the maximum Hertz stress and k k the kinematic shear yield stress. The results obtained for the RCF tests were compared with the properties of AISI 440C and SAE 52100 bearing steels. The spalls were observed using optical and electron scanning microscopy. The microstructure was found to have a strong influence in RCF results. It is concluded that ADI has good resistance to crack propagation but low resistance to crack nucleation. The RCF resistance of ADI under the present experimental conditions is not satisfactory.

Effect of Crowning Radius on Rolling Contact Fatigue Strength of Case-Hardened Steel Roller.

This paper deals with the effect of crowning radius on the rolling contact fatigue strength of case-hardened steel roller. Three types of the rollers, which had crowning radii of 30 mm, 15 mm and 7.5 mm, were fatigue-tested under a sliding rolling contact condition. The rolling contact fatigue strength of the roller became higher as the crowning radius became smaller. The failure modes of the rollers with crowning radii of 15 mm and 7.5 mm were pitting and wear, while the failure mode of the roller with a radius of 30 mm was only pitting. The pitted depth of all rollers depended almost on the depth of the maximum amplitude of the ratio of principal shear stress to Vickers hardness. The rolling contact fatigue life of the rollers could be expressed using non-dimensional value pmax/(Λ·Hυ) independent of the crowning radius, where, pmax, and Λ and Hυ are the maximum Hertzian stress, specific film thickness and Vickers hardness, respectively.

Strength-optimal running surface contour for track links

The various stresses resulting from weight, driving and tracking forces are transmitted over the contact point between track roller and track link running surface which is, compared with the dimensions of a track-type undercarriage, very small. The design of this contact point and hence the running surface profile of a track link, therefore, is particularly important. References were analyzed with the aim of discussing theoretical diversions on contact problems between plain and curved bodies to get the basis for an optimized design of the running surface profile of track-type undercarriages. Therefore stresses at point and line contact, i.e. for curved and plane running surfaces, are compared by Hertz' theory. In the case of line contact, the maximum Hertzian stress and thus also the maximum effective stresses strongly depend on the actual tilted position of the track roller to the track link running surface. The lowest stress is applied in the case of ideal line contact which is only theoretically interesting. Already at small angles of misalignment, the stresses for line contact are higher than for point contact. In field operation, at constantly changing angles of misalignment, the edge stresses cause the formation of curved running surfaces due to plastic deformation. If track links are already designed with such a running surface contour, the result will be constant stresses over the whole service life which are largely independent of the angle of misalignment avoiding excessive stresses caused by roller misalignments.

Effects of Low Speed on Roller Bearing Fatigue Life©

Two test series were conducted to study the effect of low speed and high load on the rolling-element fatigue life of 30 mm and 40 mm bore cylindrical roller bearings at inner race speeds from 19 to 3725 rpm and lubricant film parameter Lambda (λ) ratios from 0.03 to 1.2. Maximum Hertz stress ranged from 2.24 to 4.2 GPa (325 to 609 ksi). A total of 387 bearings were tested out of which 123 failed. Bearing life was directly related to transit contact lime (TT). As TT increases, life also increases. That is, bearings which run slower have longer lives in terms of bearing revolutions. A transit time life factor (LF) is suggested to be used with STLE life factors for slow moving industrial equipment roller bearings. Both TT and the total number of stress cycles affect the magnitude of measured surface residual stress induced during bearing operation. There was a relation observed between the decomposition of retained austenite and induced compressive residual stress measured on the inner-race surface. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Evaluation of fatigue and wear characteristics of M50 steel using MIL-L-7808K

The fatigue and wear characteristics of AISI VIM-VAR M50 steel were evaluated using a fully formulated polyolester based lubricant conforming to MIL-L-7808K (4 cSt at 100°C) specification. Tests were conducted using a rolling contact fatigue test rig of the ball-on-rod type at a cyclic maximum Hertzian stress level of 4.8 GPa (700 Ksi) and temperatures of 23° and 177°C. Rolling contact fatigue life results were compared with a fully formulated polyolester conforming to the MIL-L-7808J (3.2 cSt at 100°C) specification. The results suggest that rolling contact fatigue life and wear volume per stress cycle in the boundary lubrication regime are affected by lubricant type and temperature. MIL-L-7808K exhibited statistically significant superior fatigue life and lower wear rate at both temperatures when compared to MIL-L-7808J. Also, there was some correlation found between wear and fatigue life. A separate set of tests were conducted to measure rolling contact friction. Of the two lubricants evaluated, MIL-L-7808J showed the lowest average rolling contact friction.

Evaluation of fatigue and wear characteristics of M50 steel using synthetic ester turbine engine lubricants—Part 1

The fatigue and wear characteristics of AISI VIM-VAR M50 steel were evaluated using three fully formulated synthetic ester-based lubricants. Tests were conducted using a rolling contact fatigue test rig of the ball-on-rod type at a cyclic maximum hertzian stress level of 4.83 GPa (700 klbf in −2) and temperatures of 23°C (74°F) and 177°C (350°F). The lubricants evaluated included three polyol esters conforming to the MIL-L-7808J (3.16 cSt at 100°C), MIL-L-23699 (4.93 cSt at 100°C), and DOD-L-85734 (4.93 cSt at 100°C) specifications. Although preliminary results seem to suggest that rolling contact fatigue life may be affected by the type of lubricant, the differences observed were not statistically significant. Of the three lubricants tested, MIL-L-7808J generally exhibited the highest fatigue life while DOD-L-85734 showed the lowest. According to specific film thickness calculations, all three lubricants were tested under boundary lubrication. It is believed that, due to this operating lubrication regime, wear volume per stress cycle and fatigue life were unaffected by lubricant type and only affected by temperature. Also, there was some correlation found between wear and fatigue life for all lubricants.

Tribo-Characteristics of Self-Lubricating Ball Bearings for the LE-7 Liquid Hydrogen Rocket-Turbopump

The tribo characteristics of self-lubricating 40-mm-bore ball bearings with a retainer of glass cloth-polytetrafluoroelhylene (PTFE) laminate, which has elliptical pockets with a large pocket clearance, were tested under thrust loads at speeds up to 50000 rpm, 2 million DN, in liquid hydrogen (LH2) and in liquid nitrogen (LN2). During testing, the bearing torque, outer-race temperature, and electric resistance between the inner and outer races were monitored to verify the formation and rupture of a PTFE transfer film. Testing showed that the bearings having the elliptical retainer pockets were superior to the conventional bearings with circular pockets. It was determined that at the maximum inner race spinning velocity of about 5 mls a PTFE transfer film could sustain the maximum Hertz stress, up to about 2000 N/mm2, in LH2, without severe film rupture resulting in bearing seizure. In LN2, the critical load capacity of PTFE transfer film with bearing seizure was about 2700 N/mm2.

Surface fatigue life of M50NiL and AISI 9310 gears and rolling-contact bars

Spur gear endurance tests and rolling-element surface fatigue tests were conducted to investigate vacuuminduction-melted, vacuum-arc-remelted (VIM-VAR) MSONiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance characteristics, and to compare the results with those for standard VAR and VIM-VAR AISI 9310 gear material. Tests were conducted with spur gears and rolling-contact bars manufactured from VIM-VAR MSONiL and VAR and VIM-VAR AISI 9310. The gear pitch diameter was 3.5 in. Gear test conditions were an inlet oil temperature of 116°F, an outlet oil temperature of 170°F, a maximum Hertz stress of 248 ksi, and a speed of 10,000 rpm. Bench rolling-element fatigue tests were conducted at ambient temperatures with a bar speed of 12,500 rpm and a maximum Hertz stress of 700 ksi. The VIM-VAR MSONiL gears had a surface fatigue life that was 4.5 and 11.5 times that for VIM-VAR and VAR AISI 9310 gears, respectively. The surface fatigue life of the VIM-VAR MSONiL rolling-contact bars was 13.2 and 21.6 times that for the VIMVAR and VAR AISI 9310, respectively. The VIM-VAR MSONiL material was shown to have good resistance to fracture through a fatigue spall and to have fatigue life far superior to that of both VIM-VAR and VAR AISI 9310 gears and rolling-contact bars.

Stress behaviour of surface-coated materials in concentrated sliding contact

The stress behaviour at the surface and in the near-surface region of layered (surface-coated) solids in concentrated sliding contact is investigated using the finite element method. Of particular interest is the behaviour of an elastic layer on an elastic substrate normally loaded by an elastic indenter and taking account of tangential loading at the interface. Stress contour plots are generated for “hard” and “soft” layers when expressed in terms of von Mises' shear strain energy criterion normalized with respect to the maximum Hertz stress. The consequences of varying parameters such as friction coefficient, elastic modulus and layer thickness are examined.

The Adhesion and Deformation Properties of CVD TiC Coated Bearing Balls Under Heavy Loads

AbstractCVD TiC coatings on steel bearing balls have been demonstrated to improve conventionally lubricated instrument bearing performance and life, particularly where wear mechanisms predominate. Lightly loaded, approximately 1,400 (200 ksi) MPa maximum Hertz stress, coated bearing balls have run billions of load cycles without coating integrity failure. Data is presented to characterize the behavior of TiC coated steel balls under heavy loads, to approximately 4,200 MPa (605 ksi) maximum Hertz stress, for 175,000 load cycles. As in the lightly loaded tests, there was no indication of coating integrity failure, ie. cracks or delamination. At loads of 2,500 MPa (364 ksi) and above, somewhat below the elastic limit of the 440C substrate, there was evidence of plastic deformation of the coated surface.

Bending Fatigue Tests of High Speed Spur Gears

Effects of addendum modification of tooth profiles on the bending fatigue strength of high speed spur gear are discussed in this presentation: A JIS Class O Spur gear of m3, α20 deg, Z1 27, and made of AMS 6260 (AISI 9310) steel precisely ground after carburizing and hardening was meshed with the other gear of Z2 77 and operated at 8550 rpm. In this running test, bending load capacity and running performance comparisons between the gear with standard tooth profile and the two shifted gears of which tooth addendum modification coefficients were 0.35 and 0.8. The maximum normal load of the gear with addendum modification coefficient 0.8 at 107 (10 million) cycles was 1.8 kNsmm per unit tooth width. The maximum Hertz stress of this gear was 2.43 × 109 Nsm2. The allowable normal load of the gear with 0.8 was higher than that of the standard gear by 87 percent and higher than of the 0.35 profile shifted gears by 20 percent.

Analysis of Wear Debris from Full-Scale Bearing Fatigue Tests Using the Ferrograph

The Ferrograph was used to determine the types and quantities of wear particles generated during full-scale bearing fatigue test. Deep-groove ball bearings made from AISI 52100 steel were used. A MIL-L-23699 tetraester lubricant was used in a Recirculating lubrication system containing a 49-μm absolute filter. Test conditions included a maximum Hertz stress of 2.4 GPa, a shaft speed of 15 000 rpm and a lubricant supply temperature of 74°C (165°F). four fatigue failures were detected by accelerometers in this test set. In general, the Ferrograph was more sensitive (up to 23 h) in detecting spall initiation than either accelerometers or the normal spectrographic oil analysis (SOAP). Four particle types were observed: normal rubbing wear particles, spheres, nonferrous particles, and severe wear (spall) fragments. Presented at the 35th Annual Meeting in Anaheim, California, May 5–8, 1980

Ferrographic Analysis of Wear Debris Generated in Accelerated Rolling Element Fatigue Tests

Ferrographic analysis was used to determine the types and quantities of wear particles generated during accelerated rolling contact fatigue tests. The NASA five-ball rolling contact fatigue tester was used. Ball specimens were made of AMS 5749, a corrosion resistant, high-temperature bearing steel. The lubricant was a super-refined naphthenic mineral oil. Conditions included a maximum Hertz stress of 5.52 × 109 Pa and a shaft speed of 10 000 rpm. Four types of wear particles were observed; normal rubbing wear particles, fatigue spall particles, spheres, and friction polymer. Presented as an American Society of Lubrications Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977