Role In Fatigue Life Research Articles

S112014 ショットピーニング投射材硬度が浸炭硬化鋼の転がり疲労寿命に及ぼす統計的評価([S11201]機械要素の設計・製造・応用技術(1))

This study is to investigate the future possibilities of the use of the shot-peening (SP) as the final surface-finishing of carburized rolling contact machine elements. In order to investigate the influence of SP process on the rolling fatigue strength of the carburized steel, 9 kinds of specimens were fatigue tested using a thrust rolling bearing type testing machine. Four kinds of the projection particles were employed for this experiment. It was obvious by means of statistical analyses using Weibull distribution and nonparametric test that the SP process did not bring about longer fatigue life. In view of the properties on the failed surface, there is sufficient evidence to suggest that the fatigue lives of the SPed specimens might be mainly affected not by residual stress but by film thickness ratio and initial surface roughness. Furthermore, the proposed parameter A (Ac / AK) was effective to evaluate the rolling fatigue life.

Optimal Mother Wavelet Selection for Lamb Wave Analyses

Structural health monitoring (SHM) system, usually consisting of a sensor network for collecting the structural response signal and data analysis algorithms for interpreting the signal, plays a significant role in fatigue life and damage accumulation prognostics. Wavelet transform (WT) has gained popularity as an efficient means of signal processing in SHM, in which an optimal mother wavelet-based WT can carry out feature extraction with high precision. This article is to provide criteria of optimal mother wavelet selection in Lamb wave analysis for SHM, motivation of which is that small error in Lamb wave analysis can result in much larger error in damage localization because of very fast propagating velocities of Lamb waves. A concept, Shannon entropy of wavelet coefficients, was established to calibrate the degree of optimization of the selected mother wavelet. As application, various mother wavelets selected using the proposed criteria were applied to Lamb wave signals acquired from CF/EP composite laminates containing delamination. With the optimum mother wavelet, the essential information of the delamination-generated Lamb waves was achieved with high precision. The results demonstrate the excellent capacity of the approach for selecting the most appropriate mother wavelets for Lamb wave analyses and therefore damage localization.

Tribological aspects of a strain wave gearing system with specific reference to its space application

Strain wave gearing (SWG), also known as harmonic drive gear, has been used in many space applications. In 2003, a development of grease-lubricated-type SWG for space flight applications was begun. The life tests of the SWG exposed to vibration test and thermal vacuum test were performed in vacuum. The life test results showed that the in-vacuum operating life of the SWG was significantly short compared with the in-atmosphere life, which is normally corresponding to a rolling fatigue life of wave generator bearing. This may be mainly caused by the severe wear at the wave generator—flexspline interface, where the lubricant is not supplied easily into the clearance in vacuum.

Fatigue Life Estimation for Roller Bearings Under Edge Load Occurrence

For roller bearings, it is important how to design crowning profile to evade the damage by edge load and acquire the long life. Up to now, various methods for optimum crowning profile are proposed mainly from the viewpoint of contact pressure. But author thought, crowning configuration must be decided by τ0, not by contact pressure because rolling fatigue life is influenced by sub-surface shear stress amplitude τ0. To relate τ0 with bearing life, precise subsurface stress calculation is necessary. Author thought conventional uniform contact pressure element is inefficient for precise τ0 calculation, and developed a new linear pressure element. For applying τ0, which is calculated by that linear element, to fatigue life prediction, author devised new method by expanding Lundberg Palmgren theory to divided sub-surface volume. The result using this method is compared with bearing life test results. Both were corresponding well in every case. Using this method, precise life ratio prediction becomes possible, and consequently crowning profile evaluation becomes more accurate.

Performance Characteristics of Jet Fuel in Heavily Loaded Contacts

Friction coefficient, bearing performance (i.e., torque generation and temperature rise), and rolling contact fatigue of steel and ceramic (silicon nitride) materials operating in the presence of JP-8+100 jet fuel and Mil-L-23699 turbo jet oil were investigated. A ball-on-disk test machine was used to measure the coefficient of friction of a steel ball on a steel disk operating under various loads and slide-to-roll ratios when lubricated with JP-8+100 jet fuel. The results indicate that the fuel provides an extremely low friction coefficient under the conditions considered in this investigation. A three-ball-on-rod rolling contact fatigue testing machine was used to determine the fatigue life for different combinations of materials (i.e., silicon nitride and steels) and lubricants. As expected, the Weibull analysis indicates that the rolling fatigue life operating in the presence of jet fuel was less than that of an oil-lubricated contact. A bearing test machine was also designed, developed, and used to obtain the friction (torque) and the temperature characteristics of bearings operating in jet fuel and oil. The result from the bearing rig indicates that the fuel has a lower generated torque and temperature rise than oil.

Effect of the type and concentration of lubricating additives on the antiwear and extreme pressure properties and rolling fatigue life of a four‐ball tribosystem

AbstractTests were performed on two different four‐ball testers. The first was used to determine antiwear (AW) and extreme pressure (EP) properties at sliding friction. The second was used to assess the surface fatigue (pitting) life at rolling movement. Lubricating oils of various chemical compositions were tested. A base mineral oil was blended with two different commercial packages of lubricating additives of AW and EP types. The AW additives contained ZDDP and were blended with the base oil at 0.2 and 3wt %. The EP additives were organic compounds of sulphur and phosphorus, blended with the base oil at 1 and 10wt %. It is shown that AW additives not only improve AW and EP properties but also — at 0.2% — are beneficial for the fatigue life. An increase in the concentration of AW additives leads to an improvement of AW and EP properties but — for one of the packages — reduces the fatigue life. EP additives — at 1% concentration — significantly improve EP properties, and to a lesser extent AW properties. Such a concentration of EP additives has no influence on the fatigue life. An increase in the concentration of EP additives leads to a further improvement of EP and AW properties. However, this is accompanied by a considerable decrease in the fatigue life. By using a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified. Copyright © 2006 John Wiley & Sons, Ltd.

Logarithmic Profile of Rollers in Roller Bearing and Optimization of the Profile

When a bearing roller is in contact with raceways, excessive pressure peaks occur at the ends of the contact rectangles. They are called edge loading. Roller and/or raceway profiles are usually crowned to prevent edge loads. Lundberg developed a logarithmic function as a crowned profile. The profile gives an axially uniform pressure distribution. Johns-Gohar improved the function for convenience of manufacturing. However, the Johns-Gohar profile yields edge loading when the roller is tilted. Also, the profile allows no straight portion on the roller surface although it is desirable to have a flat region from the viewpoint of machining. In this study, we modified the Johns-Gohar logarithmic function to exclude edge loading even when the roller is tilted allowing a flat region. Three parameters, K1, K2 and zm, are introduced into the Johns-Gohar function. These have the following meanings : K1 : coefficient of load, K2 : ratio of crowning length to effective contact length, Zm : crown drop at edge of effective contact length zone. In addition, a mathematical optimization method is used to efficiently determine a set of the parameters. An optimization problem is considered to minimize the maximum contact pressure Pmax, or to maximize the rolling fatigue life L10. A Rosenbrock method is adopted as the optimization algorithm. The method requires no evaluation of gradients of the objective function. Pressure distribution is calculated by making use of a multilevel method. Some examples are demonstrated to verify the proposed method for both Pmax and L10.

A New Stochastic Model for Prediction of Fatigue Crack Propagation

Fatigue damage plays a significant role in fatigue life of structures and mechanical parts. Characterizing crack length as a random process in fatigue life, is a matter of controversy which is the first step of this new stochastic model for prediction of fatigue crack propagation. Minimum uncertainties and capability of using closure load are the model advantages. Generating series of a nonstationary process, effects of load history in immediate last step of crack propagation using Total Probability Theory (TPT) are some assumptions of this model. The model results have been compared with actual test results of Ti-6Al-4V CT specimens.

Rolling contact fatigue in lubricated contacts

This work presents and discusses the results of rolling contact fatigue tests (IP-300) with six different lubricants using a four-ball E.P. lubricant tester. These results tended to confirm the mechanism for rolling fatigue proposed by Jin and Kang. The lubricants tested were two mineral oils (SN 350 and SN 600) and four synthetic oils (PAG-9, PAG-12, PAO 6, and PAO X), the test machine used was a Four-Ball E.P., and the IP 300/87 standard was applied. The results indicated that: 1) lubrication has an important influence on the rolling fatigue life of mechanical components; 2) normally, in oils of the same family, the higher the viscosity is, the higher the rolling fatigue life is; 3) besides viscosity, other lubricant properties such as the pressure–viscosity coefficient (α), compressibility (B), and the EHL friction coefficient (γ), should all be taken into account for lubricated contact design.

超清浄軸受鋼製造プロセスの開発

For the miniature races and balls in spindle motors of hard disc drives, there have been required the clean bearing steel with infinitesimal oxides, Ti inclusions and sulfides which originate acoustic noises. Chita Plant, Daido Steel, has established the new process, MRAC-SSS (Multi-function Refining and Advanced Casting - Special Solution and Soaking), to manufacture the ultra clean bearing steel. Its features are as follows.(1) The tailored multi-functional refining process employing both LF and RH realizes the extremely low [O] and [Ti] levels in the molten steel.(2) The tight sealing of the tundish prevents completely the secondary oxidation of the molten steel during continuous casting.(3) The optimized reheating schedule for the cast bloom contributes to the siginificant reduction of Ti inclusions in number and size in the rolled wire or rod.The ultra clean bearing steel manufactured through the new process proves to possess the remarkably prolonged contact rolling fatigue life.

Increased adhesion of diamond-like carbon–Si coatings and its tribological properties

A pre-activation process on substrate surface has remarkably improved the poor adhesion strength of diamond-like carbon (DLC)–Si coatings on steels which is the largest obstacle in achieving a widespread application of the coatings onto machine components. The activation process consists of preliminary nitriding followed by ion etching under the selected condition. Very fine protrusions formed by the processes provide large adhesion strength to the coatings that were made continuously within the same DC-plasma-assisted chemical vapor deposition (PACVD). No intermediate layers are necessary. The critical load of DLC–Si coatings thus treated reached over 50 N in the scratch tests. The coatings with the critical load over 50 N showed much improved rolling fatigue life. The DLC–Si coating with over 50 N critical load endured a rotationa1 stress of 10 8 cycles at a contact pressure of 3.4 GPa, whereas the DLC–Si coatings with 10 N spalled at 10 6 cycles.

Stress history in rolling–sliding contact of rough surfaces

An investigation into the non-Hertzian, elastic stress history, due to the contact of two rough surfaces is presented. A complex evolution of stress is produced whose magnitude and rate depend strongly upon the roughnesses and speeds of the contacting bodies. The key features of the stress fields are illustrated by plots of stress versus time and horizontal distance, for a range of depths and for various contact conditions. The stresses near the surface are many times higher than in an equivalent smooth contact and the roughness on the counterface generates a moving stress field which, when sliding is present, greatly increases the number of cycles of stress during each passage of the contact. This may account, in part, for the observation that the rolling fatigue life of hard steels declines more rapidly with sliding speed for rough, than for smooth surfaces and suggests that counterface roughness is especially important in determining the fatigue life.

Effects of pre-rolling and metal removal on the fatigue life of lubricated rolling/sliding contact

In this experiment, after the test specimens are preloaded at different first-step rolling cycles, the surface layer of the lower speed roller is ground to different depths by a grinder along the radial direction. With a new higher speed roller, the effects of the ground depth and first-step rolling cycle on the fatigue life of lubricated rolling/sliding contact are investigated using a 0.45% carbon steel pair. Results show that the prerolling cycles with metal removal can improve the rolling fatigue life. It is found that when the surface hardness of the specimen starts to approximate the saturated value at the first-step rolling cycle with the ground depth to the position of its maximum hardness, the rolling fatigue life with this preloading operation is 3.3 times that with the normal operation for the second-step load of 588 N. This increment in the rolling fatigue life can be reasonably explained by the measured plastic flow of the surface layer and the theoretical results of the residual stress below the contact surface.

Strain-controlled fatigue properties of Ti 3Al based alloy : Cao, J., Sun, F., Cao, C. and Gao, Y. Xiyou Jinshu Cailiao yu Gongcheng (Rare Metal Materials and Engineering) (1996) 25, 17–20

This work has evaluated the rolling-contact fatigue lives of AISI 52100 steel balls with several mineral and synthetic oils with and without additive using a four-ball tester. The studied lubricants include S.N.-350 (mineral oil), S.N.-600 (mineral oil), TMP-05 (synthetic polyol ester), TMP-05 + 2%ZnDDP, P.A.G.-9 (synthetic polyalkyl glycol), P.A.G.-12 (synthetic polyalkyl glycol) and Breox-B-135X (synthetic polyalkyl glycol). Weibull plots and S-N (stress-number of cycles) of L10 and L50 are given to all the tested oils. Pressure-viscosity coefficients for different tested oils are estimated experimentally for understanding the fatigue test results. The results indicate: (1) synthetic polybutene HYVIS-07 gives the longest rolling-contact fatigue life to AISI 52100 steel balls among all the mineral and synthetic oils studied in the present work, which may be attributed to its highest pressure-viscosity coefficient among the tested oils; (2) the rolling fatigue performance of a synthetic oil can be better or worse than that of a mineral oil, depending on the nature of the synthetic oil family. The capability of improving the rolling fatigue lives of tested mineral and synthetic oils increases in the order synthetic polyol ester, synthetic polyalkyl glycol, mineral oil, and synthetic polybutene; (3) a higher viscosity oil will lead to a longer rolling life, but the influence of viscosity in synthetic oil on the rolling fatigue life of steel balls will be less than that of changing synthetic oil family; (4) synthetic oil with E.P. antiwear additive has al longer rolling fatigue life compared with the case without additive.

Rolling-contact fatigue lives of steel AISI 52100 balls with eight mineral and synthetic lubricants

This work has evaluated the rolling-contact fatigue lives of AISI 52100 steel balls with several mineral and synthetic oils with and without additive using a four-ball tester. The studied lubricants include S.N.-350 (mineral oil), S.N.-600 (mineral oil), TMP-05 (synthetic polyol ester), TMP-05 + 2%ZnDDP, P.A.G.-9 (synthetic polyalkyl glycol), P.A.G.-12 (synthetic polyalkyl glycol) and Breox-B-135X (synthetic polyalkyl glycol). Weibull plots and S-N (stress-number of cycles) of L 10 and L 50 are given to all the tested oils. Pressure-viscosity coefficients for different tested oils are estimated experimentally for understanding the fatigue test results. The results indicate: (1) synthetic polybutene HYVIS-07 gives the longest rolling-contact fatigue life to AISI 52100 steel balls among all the mineral and synthetic oils studied in the present work, which may be attributed to its highest pressure-viscosity coefficient among the tested oils; (2) the rolling fatigue performance of a synthetic oil can be better or worse than that of a mineral oil, depending on the nature of the synthetic oil family. The capability of improving the rolling fatigue lives of tested mineral and synthetic oils increases in the order synthetic polyol ester, synthetic polyalkyl glycol, mineral oil, and synthetic polybutene; (3) a higher viscosity oil will lead to a longer rolling life, but the influence of viscosity in synthetic oil on the rolling fatigue life of steel balls will be less than that of changing synthetic oil family; (4) synthetic oil with E.P. antiwear additive has al longer rolling fatigue life compared with the case without additive.

Ceramic Hybrid Bearings in Air-Cycle Machines

Extensive research in the field of ceramic rolling contact bearings has been conducted over the past several years. The results of this research indicate that silicon nitride may offer significant improvements in rolling fatigue life and a possible increase in operating temperature. AlliedSignal Aerospace Systems & Equipment (ASE) and the Air Force Item Management Engineering Branch at Tinker Air Force Base are conducting a development program under contract to ARPA to introduce ceramic hybrid bearings into existing F-15, F-111, and C-130 aircraft fleets in a near-term program involving retrofitting mature air-cycle machines with such bearings. The air-cycle machine (ACM) is a complex bearing application, operating at very high speeds (up to 100,000 rpm) and at high temperatures. In more severe military ACM applications, mean times between failures (MTBFs) of 2000 and 3000 hours are common. The fleet would see an immediate benefit from improved bearing life. This paper describes the analytical approach to evaluating and comparing ceramic to steel bearings, describes the laboratory test program to verify performance, and discusses the life-cycle cost improvement and the flight test program.

転動疲労寿命に及ぼす圧こん縁の盛り上がりと残留オーステナイトの影響

A typical damage of bearings used in contaminated lubricants is caused by increasing of shearing stress at dents due to harder wearing particles in the lubricants.In this study, SUJ2 steel was used as the test material in which the amount of retained austenite and hardness were changed under various heat treatments. Rolling fatigue tests were repeated by the use of specimens having sharp dents intruded by a Vickers indenter. From the results of the rolling fatigue tests, the effect of the retained austenite on the fatigue life was investigated, considering the work hardening of the dent ridge.The main results were obtained as follows.(1) Retained austenite changed into martensite under rolling load and induced work hardening of the ridge, and then further shape changes of the ridges were virtually prevented.(2) As the dent with ridge caused the flaking of the rolling surface that occurred under shearing stress, the optimizing amount of retained austenite must be found for rolling fatigue life.(3) The upper amount of retained austenite was 20∼30 vol%, judging from the surface hardness, work hardening, life range and toughness.Based on the present results, the taper roller bearings which were controlled 20∼25 vol% retained austenite in the surface layer (10 μm depth from surface) and the surface hardness of 800∼860 HV were made. These bearings showed 11.3 times longer life than the conventional ones in contaminated oil. It was proved that the retained austenite had a significant effect on the formation and elimination of these ridges.

窒素けい素軸受球の転がり疲労特性

Rolling fatigue tests were carried out on hot isostatically pressed silicon nitride bearing balls. At three load levels of the maximum Hertzian contact pressure pmax=5900, 6740 and 7110MPa, 13 balls each were tested, and the life distribution was studied. It was found that the rolling fatigue life followed approximately a 2-parameter Weibull distribution with the shape parameter of α≅1 at each load level. The relationship pmaxκL50=const (κ≅10) was found between pmax and the median life L50. Microscopic observation of flaking was also performed, and two types of flaking were found. One is flaking with the depth of the order of 100μm, and the other is a shallower one. The depth of the former type was found to coincide approximately with the depth at which the maximum shear stress occurred. At lower load levels, the former type was dominant. Frequency of appearance of the latter type increased with an increase in load level. Comparing the shape parameter of α≅1 and the exponent of κ≅10 mentioned above with those for the cyclic bending fatigue of plain specimens of silicon nitride, it was suggested that the mechanism of rolling fatigue of silicon nitride was different from that of cyclic bending fatigue of the same material.

セラミックス製ボールねじの試作 (第2報)

In the 1st report, the applicability of alumina ceramics (Al2O3) to ball screws was studied by rolling fatigue life test using the simplified cylindrical model of ball screws. In this report, the applicability of silicon nitride (Si3N4) and Sialon (SiAlON) ceramics was also studied by the same method. It was clarified by the test that the surface roughness of both materials had influence on the life and the basic dynamic capacities of both materials were 10% of that of bearing steel (SUJ 2) when the test pieces had good surfaces. SEM observation made it clear that the fracture occurred at the outskirts of ceramics pores in the same process as the fracture of the alumina. As a result, the applicability order of 3 ceramics are the silicon nitride, Sialon and alumina.

過冷オーステナイト状態の軸受鋼切削加工のための熱間鍛造からの連続熱処理

A new machining process, called auscutting, has been developed in which the cutting operation is per-formed in supercooled austenitic state during quenching. In this paper, the optimum heat cycle condition which saves much thermal energy and time in the continuous process for manufacturing bearing races from hot forging to auscutting is investigated from the viewpoint of the quenched structure. Furthermore, under the obtained optimum heat cycle condition, the machinability and the rolling fatigue life are investigated.The results obtained are summarized as follows:(1) The optimum heat cycle process with auscutting is (hot forging)→(air cooling to 650°C)→(slow heating to 850°C and soaking)→(quenching to 200°C)→(auscutting)→(air cooling). Thermal energy in this process with auscutting is about 36% less than that in the conventional process.(2) Under the optimum heat cycle, the machinability in auscutting is not worse than that under theconventional heat cycle and the rolling fatigue life is about 3-4 times longer than that under the conven-tional heat cycle.