Steels for bearings

This paper summarises the keynote talk opening the session on ‘Critical Distance Theories of Fracture’; my aim is to describe the methodology used, to demonstrate its applicability in predicting experimental data on fracture and fatigue, to discuss the fundamental basis of the theory and, to suggest areas for future work in this field. The Theory of Critical Distances (TCD) is the name which I have given to a group of theories used for predicting the effects of notches and other stress-concentration features. These theories have a long history, but currently they are being investigated by only a small number of researchers worldwide. This is a pity, because the TCD is capable of accurate predictions in a wide variety of situations. The essential elements are an elastic stress analysis and a material-dependent critical distance, a parameter which we call L. The value of L can be written in terms of other material parameters as: 

$$ L = \frac{1} {\pi }\left( {\frac{{K_c }} {{\sigma _o }}} \right)^2 $$

(1)

The Theory of Critical Distances

Roles of microstructure in fatigue crack initiation

A technique is described for the measurement of the residual stress tensor averaged over a specified volume within a component. The method involves measurement of small changes in lattice spacing using high resolution neutron diffraction. The stress is inferred from these measurements of the strain, and the theory of the relationship between the two quantities is described, including the effects of crystalline anisotropy. The various types of high resolution neutron diffractometer suitable for the work are described. Experimental results validating the method are given for a simple bent bar of mild steel of known strain, a plastically strained mild steel bar, and a mild steel tube of known torsional strain. Examples of the method in practical use are given by a cracked fatigue test specimen, a double-V test weld and a weld joining a tube to a plate. A more detailed example is the anisotropic response of a polycrystalline sample under elastic and plastic strain; this is illustrated by measurements...

Neutron diffraction methods for the study of residual stress fields

Characterization and analysis of delamination fracture in composites: An overview of developments from 1990 to 2001

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

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

Fatigue strength of spring steel under axial and torsional loading in the very high cycle regime

Mode II fatigue crack growth from delamination in unidirectional tape and satin-woven fabric laminates of high strength GFRP

The misorientation introduced into an austenitic stainless steel (SUS 316) by plastic deformation was masured with the electron back scattering diffraction (EBSD) and the X-ray diffraction (XRD) techniques. Three parameters related to miorientation distribution, i.e. grain orientation spread (GOS), grain average misorientation (GAM) and kernel average misorientation (KAM), were calculated from the orientation measurements by EBSD. The misorienation between neighboring measured points, KAM, was larger close to the grain boundary where the slip propagation was difficult. The average of misorientation between neighboring points within one grain is GAM. The GAM value averaged over the measured reagion increased proportionally with the plastic strain to about 20%, and leveled off at higher strains. The average of the misorientation spread within one grain, GOS, also showed similar increase like GAM. The total misorientation of a grain measured by XRD also showed a proportional increase with the plastic strain to about 10%, and it was difficult to measure the total misorientation above that strain because Debye ring became continuous ring. Both EBSD and XRD can be used as a tool to measure the plastic strain in the local area, and the limit of strain to be measured was 30% for the former and 10% for the latter.

Keisuke Tanaka

Papers

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

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

Fatigue strength of spring steel under axial and torsional loading in the very high cycle regime

Mode II fatigue crack growth from delamination in unidirectional tape and satin-woven fabric laminates of high strength GFRP

Misorientation analysis of plastic deformation of austenitic stainless steel by EBSD and X-ray diffraction methods