A Theoretical Analysis of Shear Stresses and Roller Slip in Rolling Bearings During Low-Temperature Starting

1997 ◽  
pp. 423-444 ◽  
Author(s):  
V. Wikström ◽  
R. Larsson ◽  
E. Höglund
Keyword(s):  
Low Temperature ◽  
Theoretical Analysis ◽  
Shear Stresses ◽  
Rolling Bearings

The Effect of the EHD Pressure Spike on Rolling Bearing Fatigue

1987 ◽  
Vol 109 (3) ◽  
pp. 444-450 ◽  
Author(s):  
L. Houpert ◽  
E. Ioannides ◽  
J. C. Kuypers ◽  
J. Tripp
Keyword(s):  
Pressure Distribution ◽  
High Stress ◽  
Surface Damage ◽  
Rolling Bearing ◽  
Shear Stresses ◽  
Stress Concentrations ◽  
Surface Layers ◽  
Rolling Bearings ◽  
Life Model ◽  
Pressure Spike

A recently proposed fatigue life model for rolling bearings has been applied to the study of lifetime reduction under conditions conducive to microspalling. The presence of a spike in the EHD pressure distribution produces large shear stresses localized very close to the surface which may account for early failure. This paper describes a parametric study of the effect of such spikes. Accurate stress fields in the volume are calculated for simulated pressure spikes of different height, width and position relative to a Hertzian pressure distribution, as well as for different lubricant traction coefficients and film thicknesses. Despite the high stress concentrations in the surface layers, reductions in life predicted by the model are modest. Typically, the pressure spike may halve the life, with the implication that subsurface fatigue still dominates. In corroboration of this prediction, preliminary experimental work designed to reproduce microspalling conditions shows that microindents due to overrolling particles are a much more common form of surface damage than microspalling.

scholarly journals Tangential forces in the contact area of upper road layer with the base

2018 ◽  
Vol 239 ◽  
pp. 05012 ◽  
Author(s):  
Timmo Gavrilov ◽  
Gennady Kolesnikov ◽  
Konstantin Khoroshilov
Keyword(s):  
Low Temperature ◽  
Contact Area ◽  
Piecewise Linear ◽  
Shear Stresses ◽  
Shear Forces ◽  
The Road ◽  
Concrete Layer ◽  
Order Polynomial ◽  
Low Temperature Cracking ◽  
Tangential Forces

Low-temperature cracking is one of the main reasons for the deterioration of the upper layer of roads in regions with cold winters. A large number of works focused on deterioration prevention are known, however the interdisciplinary problem of low-temperature cracking remains relevant. The important, but insufficiently studied factor is the distribution of normal and tangential (shear) forces acting on the upper layer of the road. The objective of the current study was to clarify insight about the distribution of tangential forces in the contact area of the upper layer of the road with the base. There are works in which it is assumed that these forces are distributed by a piecewise linear law. We propose a mechanical and mathematical model and an analytical solution to the problem of the distribution of shear forces in the contact area of the upper layer with the base. The main result of the study: it is found that the distribution of shear forces in the segment of the asphalt concrete layer is described by a second-order polynomial. However, the shear stresses are distributed linearly over the entire length of the segment and reach the highest modulo values in the area of the end sections of the segment. The results of the presented study clarify the understanding of functioning of the upper road layer at low temperatures. By that, the contribution to the solution of the problem of increasing the crack resistance of roads in regions with cold winters is made.

scholarly journals How Nanoscale Dislocation Reactions Govern Low- Temperature and High-Stress Creep of Ni-Base Single Crystal Superalloys

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 134 ◽  
Author(s):  
David Bürger ◽  
Antonin Dlouhý ◽  
Kyosuke Yoshimi ◽  
Gunther Eggeler
Keyword(s):  
Low Temperature ◽  
Single Crystal ◽  
High Stress ◽  
Shear Stresses ◽  
Creep Tests ◽  
Shear Creep ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Crystallographic Shear ◽  
Shear System

The present work investigates γ-channel dislocation reactions, which govern low-temperature (T = 750 °C) and high-stress (resolved shear stress: 300 MPa) creep of Ni-base single crystal superalloys (SX). It is well known that two dislocation families with different b-vectors are required to form planar faults, which can shear the ordered γ’-phase. However, so far, no direct mechanical and microstructural evidence has been presented which clearly proves the importance of these reactions. In the mechanical part of the present work, we perform shear creep tests and we compare the deformation behavior of two macroscopic crystallographic shear systems [ 01 1 ¯ ] ( 111 ) and [ 11 2 ¯ ] ( 111 ) . These two shear systems share the same glide plane but differ in loading direction. The [ 11 2 ¯ ] ( 111 ) shear system, where the two dislocation families required to form a planar fault ribbon experience the same resolved shear stresses, deforms significantly faster than the [ 01 1 ¯ ] ( 111 ) shear system, where only one of the two required dislocation families is strongly promoted. Diffraction contrast transmission electron microscopy (TEM) analysis identifies the dislocation reactions, which rationalize this macroscopic behavior.

Rheological Inactivity of AIMgSi Conductors (AAAC) in Trend of Negative Stress Gradients

2013 ◽  
Vol 765 ◽  
pp. 808-812
Author(s):  
Beata Smyrak ◽  
Tadeusz Knych ◽  
Andrzej Mamala ◽  
Kinga Korzeń
Keyword(s):  
Low Temperature ◽  
Theoretical Analysis ◽  
Aluminium Alloy ◽  
Stress Drop ◽  
Research Results ◽  
Stress Gradients ◽  
Temperature Creep ◽  
The Wire ◽  
Low Temperature Creep

The authors of this paper present the research results of low temperature creep of AlMgSi (6101) wires and AAAC - All Aluminium Alloy Conductor. The conductor is made from AlMgSi wires (diameter 2.99 mm). Based on theoretical analysis it was proved that creep of an overhead conductors depends on the relation between stress and temperature of conductor and the span geometry. Thus the objective of the paper is to determine the wire and conductor creep under the conditions of stress drop. On the basis of the research it has been observed that the creep of both the AAAC conductor and the AlMgSi wires temporarily stopped.

Lundberg-Palmgren Fatigue Theory: Considerations of Failure Stress and Stressed Volume

1999 ◽  
Vol 121 (1) ◽  
pp. 85-89 ◽  
Author(s):  
T. A. Harris ◽  
Wei Kuei Yu
Keyword(s):  
Life Prediction ◽  
Fatigue Cracking ◽  
Shear Stresses ◽  
Rolling Bearings ◽  
Surface Shear ◽  
Cross Sectional ◽  
Stressed Volume ◽  
Bearing Raceway ◽  
Distribution Of Stress ◽  
Maximum Contact

Load ratings and fatigue life prediction of rolling bearings is based on the Lundberg-Palmgren theory first published in Sweden in 1947. The basic equation of this theory includes the stressed volume of material in the bearing raceway subsurfaces as a major parameter. This volume of material is simplistically determined to have a nearly rectangular subsurface cross-sectional area bounded by the length of the maximum contact area ellipse and the depth at which the maximum failure-causing stress occurs. The latter stress is assumed to be effective over this area. In fact, a distribution of stress occurs, and in this investigation it is demonstrated that the subsurface volume with a potential for fatigue cracking is substantially different from that used by Lundberg and Palmgren. This difference in volume, particularly in the presence of surface shear stresses, can have a profound effect on the method and prediction of bearing fatigue lives.

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