A, tangential force
Imported Construction Of TIMKEN 67388 Bearings http://www.fagbearings-hk.com/newproduct/TIMKEN-67388-bearings-80741.html in actual running along the tangential friction resistance in contact surface exists, in elastohydrodynamic lubrication, the tangential friction force. The existence of the tangential force makes the static shear stress and the orthogonal shear stress values increase, and the depth from surface. Line contact, when the friction coefficient is greater than 0.11, the maximum static shear stress occurs on the contact surface; Point contact, when the friction coefficient is 0, 25, the maximum static shear stress occurs on the contact surface.
Second, the residual stress and ring to stress
Imported bearing steel during heat treatment of retained austenite to martensite transformation process will produce residual stress, and stress cycle times the increase of the number will affect the measurement of surface residual stress. On the analysis of the residual stress shows that residual stresses are present in the depth of the maximum shear stress will increase with the decrease of the maximum shear stress of life. Such as residual stress, reduce the maximum shear stress lO % can make double rolling bearing fatigue life. Residual tensile stress and reduce the bearing life. When selecting of the bearings are too tight or high rotational speed and centrifugal force, can produce rings in the rolling element and ring to should force, internal ring ring to force and has a great influence on the whole bearing life, such as inner diameter 40 ram of angular contact ball bearing, rotating speed of 1500 r/min, the life about reducing 11% ~ 17 z, and rotational speed at 3000 r/min, the life can be reduced about 21% ~ 22%.
Three, fatigue limit stress
Ioannid. S et al., put forward the concept of fatigue limit of bulk materials, and think that the failure should not only consider the maximum volume of alternating shear stress at the top of the volume, and the stress shall be taking into account the influence of the volume; And if the stress of the volume of maximum stress is less than the fatigue stress of material, material won't appear the fatigue phenomenon, this part will show almost infinite fatigue life. A, Za. T. Ky feel that the introduction of the fatigue limit will improve life - load index, overestimate the bearing's life.
Four, the surface roughness and the influence of EHL lubrication (film thickness ratio)
Surface roughness and the impact of EHL lubricant of life is to receive, in the film thickness ratio is shown in figure 1-5, when the film thickness than A > 3, the service life of bearing is bigger than the rated life, this state is called full elastohydrodynamic lubrication state, in the actual use of bearing mostly in part elastohydrodynamic state one 1 ~ 2 (A).
Five, the influence of surface treatment
Roller and race surface treatment technology can change the roller surface hardness, residual stress distribution and the overall strength, thus improve the service life of bearing. For high frequency hardening, laser hardening, carburizing and hardening process of roller, the deeper hardening layer, roller, the greater the fatigue strength is not necessarily exist an optimal hardening depth. For the nitriding, soft nitriding roller, roller increases with the increase of fatigue strength as the hardening depth. In addition, the surface hardening treatment also should consider the effect of surface roughness and residual stress.
Sixth, the effect of pollution particles in the lubricating oil
Lubricating oil pollution particles into the two contact surfaces, in the raceway surface indentation, when after creasing roller, the edges of the indentation can produce stress concentration and crack, crack extending gradually along with the stress cycle repeated, end up surface spalling. Most real industrial use of the bearing with the surface spalling and failure in the end. Pollution particles, the higher the hardness, the greater the reduced life spans. Particles of life must also and the influence of the contact ellipse parameters, the smaller the contact ellipse parameters, the greater the impact on life.
Seven, the influence of temperature on the fatigue life
FAG bearings after continuous operation, with certain temperature, the temperature rise of bearing fatigue life will have influence, especially the contact area of the fever. This kind of the temperature range and the lubricating oil film thickness between the contact pair, the contact parts of surface features and load, speed and other parameters. Eight, running speed on the fatigue life research shows that the influence of the bearing fatigue life of direct contact with the transient time, namely under the maximum load contact roller inside is rolled on and the time needed for inner ring raceway contact ellipse width. With the increase of the instantaneous contact time, the fatigue life of bearing will increase, in addition, the instantaneous contact length will affect the surface residual stress, which indirectly affect the fatigue life.
The influence of nine, not failure life for life
For survival in 0.4 ~ o. 93 within the scope of the bearing, its life obeys two parameter weibull distribution, beyond this range should be introduced not failure life (minimum bearing life) to distributed in life, to get three parameter weibull lifetime distribution: s - exp
Ten, the influence of material purity (oxygen)
Material purity is higher, the higher the bearing life, figure 1-6 for AISA52100 steel, surface carburizing steel oxygen content and the relationship between fatigue life. § 1-3 the primary technical measures to improve the fatigue life of rolling bearing from the causal effect of fatigue mechanism, failure modes, can adopt the corresponding technical measures, to ensure and improve the fatigue life of bearing