In recent years, mechanical structures such as railway wheels, rails, offshore structures, bridges, engine components, load bearing parts of automobiles, etc. have to endure for a long term up to 108-1010 loading cycles in order to save resources and to reduce the cost together with the environmental load to the globe. Thus, the fatigue behavior of structural materials in the very high cycle regime of 108-1010 cycles has become an important subject of the research. In this paper, a review of the current studies in this area performed by many researchers is described in order to provide a certain milestone in the history of the research on fatigue behavior of the metallic materials in the very high cycle regime.

Review and Prospects for Current Studies on Very High Cycle Fatigue of Metallic Materials for Machine Structural Use

The crack propagation law was derived from the S-N data in the very high cycle fatigue of a bearing steel. The propagation rate, da/dN (m/cycle), of surface cracks was estimated to be a power function of the stress intensity range, ΔK (MPa√m) with the coefficient C s = 5.87 x 10- 13 and the exponent m s = 4.78. The threshold stress intensity range was 2.6MPa√m. The crack propagation from internal inclusions was divided into Stages I and II. For Stage I, the coefficient of the power law was C o = 3.44 x 10 -21 and the exponent m o = 14.2. The transition from Stage I to II took place at ΔK = 4.0 MPa√m. For Stage II, the coefficient was C i = 2.08 x 10 -14 and the exponent m i = 4.78. The specimen size and loading mode did not influence the surface fatigue life, while the internal fatigue life was shortened in larger specimens and under tension-compression loading. For ground specimens, the surface fatigue life was raised by the compressive residual stress, while reduced by the surface roughness introduced by grinding. For shot-peened specimens, fatigue fracture did not take place from the surface because of a high surface compressive residual stress. The internal fatigue life was reduced by the tensile residual stress existing in the interior of the specimens.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1460-2695.2002.00547.x

Fatigue crack propagation behaviour derived from S–N data in very high cycle regime

Effect of stress ratio on long life fatigue behavior of high carbon chromium bearing steel under axial loading

Very high cycle fatigue properties of bearing steel under axial loading condition

The nature and the mechanism of crack initiation and early growth for very-high-cycle fatigue of metallic materials – An overview

In order to clarify the fatigue behavior in a wide life region, fatigue tests in the life region of N=0.5a(10)9 were performed for high strength steel of SUJ2, by means of a multi-type testing machine developed here. Thus, it was found that the S-N curve in the medium life region can be straightforwardly extrapolated to the low cycle region and connected to the static strength which provides the fatigue strength at N=0.5. It is another finding that S-N property of this steel in such a wide life region was successfully explained as duplex S-N characteristics corresponding to the surface induced fracture and interior inclusion induced fracture with a fish-eye, respectively. Characteristic fracture surface so-called fine granular area (FGA) was formed in the vicinity at the inclusion at the center of the fish-eye. Consequently, the long life fatigue fracture of this steel was caused through three different processes of (1) formation of FGA, (2) crack propagation to form the fish-eye and (3) rapid crack propagation to cause the catastrophic fracture.

https://www.jstage.jst.go.jp/article/kikaia1979/67/663/67_663_1805/_pdf

S-N Property and Fractography of High Carbon Chromium Bearing Steel over Ultra Wide Life Region under Rotating Bending.

Rotating bending fatigue tests were performed for a high carbon-chromium steel in order to clarify the influence of radical nitriding on fatigue strength and fracture mechanism in the life region where a fish-eye fracture occurs. It was found that crack intiation originated from slips or surface defects under high stress levels and from internal defects under low stress levels in the both quenched and tempered steel and nitrided steel. However, fatigue life in the fish-eye fracture region was extremely shorter in the nitrided steel than in the quenched and tempered steel. Around the non-metallic inclusion of fish-eye, granular facets were observed in the quenched and tempered steel but in the nitrided steel featureless facets generated. Macroscopic examination of fish-eye fracture surfaces also showed that in the quenched and tempered steel, a crack propagated radically with a start at fish-eye, but in the nitrided steel it grew rapidly within diffusion layer and then extended internally from the whole diffusion layer to form a ring-shaped fracture surface.

https://www.jstage.jst.go.jp/article/kikaia1979/66/651/66_651_2036/_pdf

Fatigue Strength of Radical Nitrided Bearing Steel.

In reliability assessment of mechanical structures in the long period, it is important to clarify the fatigue characteristics in such a long sequence of cyclic loading. Thus, ultra-long life fatigue properties of SCM 435 steel were experimentally examined in rotating bending. In addition, high cycle fatigue data of the same kind of steels were extracted from the Database on Fatigue Strength of Metallic Materials published by JSMS. These results and original data obtained by the authors were put altogether, and the statistical fatigue properties of this kind of steels were analyzed as duplex P-S-N characteristics.

https://www.jstage.jst.go.jp/article/kikaia1979/70/696/70_696_1102/_pdf

Nobuaki Tanaka

Papers

S-N Property and Fractography of High Carbon Chromium Bearing Steel over Ultra Wide Life Region under Rotating Bending.

Fatigue Strength of Radical Nitrided Bearing Steel.

Statistical Fatigue Properties in Ultra-Long-Life Regime for SCM 435 Steels Based on JSMS Database on Fatigue Strength of Metallic Materials