Notch effect on fatigue strength reduction of bearing steel in the very high cycle regime

It is known that welded joint is much “weaker” than base metal due to discontinuities of geometry, materials and residual stresses. It seems current international design rules do not adopt a uniform approach to weld efficiency, which is often defined as the ratio of the strength of a welded joint to the strength of base metal, in their guidance for creep and fatigue design of welds. This appears to be a great barrier for the application of nuclear welded structures which has a prolonged design lifetime of 60 years. In this work, fatigue strength reduction factor of a Cr-Ni-Mo-V steel welded joint, machined from welded steam turbine rotors for nuclear power plant, was investigated by performing axially push-pull cyclic loads tests with both cross-weld and pure base metal specimens up to very high cycle fatigue regime under ultrasonic frequency at ambient temperature. The effects of residual stress, strain localization, and microdefects in mismatched steels on failure mechanisms of welds were discussed thoroughly. Results show that fatigue strength reduction factor is varied in the range of 0.95-0.975, and is found to be dependent on fatigue lifetime for the first time. It is indicated that variation of fatigue strength reduction factor are associated with transition of crack initiation from specimen surface in high cycle fatigue regime to interior micro-defects in very high cycle fatigue regime. Comparing existing codes and standards for fatigue design of welds with experimental data indicates the over-conservativeness of present code-based design method. This implies a micro-defect based fatigue design approach is required for long life safe and reliability of weldments.

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On the determination of the bending fatigue strength in and above the very high cycle fatigue regime of shot-peened gears

Forschung im Ingenieurwesen ◽

10.1007/s10010-021-00499-2 ◽

2021 ◽

Author(s):

D. Fuchs ◽

S. Schurer ◽

T. Tobie ◽

K. Stahl

Keyword(s):

Fatigue Strength ◽

High Cycle Fatigue ◽

Load Carrying Capacity ◽

Cycle Fatigue ◽

Bending Fatigue ◽

Very High Cycle Fatigue ◽

Bending Load ◽

Load Carrying ◽

Bending Fatigue Strength ◽

Very High

AbstractDemands on modern gearboxes are constantly increasing, for example to comply with lightweight design goals or new CO2 thresholds. Normally, to increase performance requires making gearboxes and powertrains more robust. However, this increases the weight of a standard gearbox. The two trends therefore seem contradictory. To satisfy both of these goals, gears in gearboxes can be shot-peened to introduce high compressive residual stresses and improve their bending fatigue strength. To determine a gear’s tooth root bending fatigue strength, experiments are conducted up to a defined number of load cycles in the high cycle fatigue range. However, investigations of shot-peened gears have revealed tooth root fracture damage initiated at non-metallic inclusions in and above the very high cycle fatigue range. This means that a further reduction in bending load carrying capacity has to be expected at higher load cycles, something which is not covered under current standard testing conditions. The question is whether there is a significant decrease in the bending load carrying capacity and, also, if pulsating tests conducted at higher load cycles—or even tests on the FZG back-to-back test rig—are necessary to determine a proper endurance fatigue limit for shot-peened gears. This paper examines these questions.

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Surface Cross-linked UHMWPE: A Low Wear Material with Very High Fatigue Strength

The Journal of Arthroplasty ◽

10.1016/j.arth.2010.01.080 ◽

2010 ◽

Vol 25 (3) ◽

pp. e72

Author(s):

Ebru Oral ◽

Bassem Ghali ◽

Shannon Rowell ◽

Brad Micheli ◽

Orhun Muratoglu

Keyword(s):

Fatigue Strength ◽

High Fatigue ◽

Low Wear ◽

Very High

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Effect of Repeated Quenching on the Rotating Bending Strength of SAE52100 Bearing Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.457-458.1025 ◽

2012 ◽

Vol 457-458 ◽

pp. 1025-1031 ◽

Cited By ~ 5

Author(s):

Koshiro Mizobe ◽

Edson Costa Santos ◽

Takashi Honda ◽

Hitonobu Koike ◽

Katsuyuki Kida ◽

...

Keyword(s):

Fatigue Strength ◽

Bending Strength ◽

High Strength ◽

Bearing Steel ◽

Rolling Contact ◽

High Wear Resistance ◽

High Carbon ◽

Austenite Grain ◽

High Fatigue ◽

Rotating Bending

Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance are required. Due to its high fatigue strength, SAE 52100 is recently being used not only for the production of bearings but also shafts. Refining of prior austenite grain through repeated quenching is a procedure that can be used to enhance the material’s strength. In this work, the microstructure of repeatedly quenched SAE 52100 steel and its fatigue strength under rotating bending were investigated. It was found that repeated furnace heating and quenching effectively refined the martensitic structure and increased the retained austenite content. Repeated quenching was found to improve the fatigue strength of SAE 52100.

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