The SKF Generalized Bearing Life Model is (GBLM) an innovative new bearing rating life model that is designed to help engineers calculate bearing rating life in a more realistic manner. The new model is a major step forward for the industry and will play an important role in enabling OEMs and end users to better match bearings and applications, resulting in improved machine life and reduced operating costs.

The fundamentals of the new model are presented here.
Up to now the estimation of rolling bearing life has relied
on engineering models that consider an equivalent
stress—originated beneath the contact surface—that is applied
to the stressed volume of the rolling contact. Through
the years, surface-originated fatigue resulting from reduced
lubrication or contamination has been incorporated into
the estimation of the bearing life by applying a penalty to
the overall equivalent stress of the rolling contact. In the SKF
GBLM this issue is addressed by developing a general approach
for rolling contact life in which the surface-originated
damage is explicitly formulated into the basic fatigue equations
of the rolling contact. This new formulation supplies the
power to better represent the tribology of rolling bearings in
rating life calculations. Further, it gives a better knowledge of
the surface endurance that dominates the field performance
of rolling bearings. The ability of the present general method
to account for the tribology and surface-subsurface competing
fatigue mechanisms taking place in rolling bearings is
discussed.

Modern rolling bearings have become increasingly reliable
when correctly used and lubricated. This is due to good practices
and the successful understanding and application of
the traditional rolling contact fatigue mechanisms. Increased
material cleanliness and good manufacturing quality, combined
with reliable life-rating methods, have made this possible.
However, industrial trends of downsizing and higher
demands for efficiency in field performance keep imposing
additional, severe conditions upon rolling bearings—especially
on the contacting surfaces. This is why most bearing
failures are surface-related (Ref.1). In order to prevent rolling
bearings from causing a bottleneck in furthering the performance
increase of modern machinery, the tribology of bearing
surfaces must be better assessed with respect to bearing
performance. In the past decade SKF has made substantial
progress in the surface life modeling area (Refs. 2–8). Finally,
the integration of this knowledge into rolling bearing life rating
has been made possible (Ref.9) with the introduction of
the SKF generalized bearing life model (GBLM). It separates
surface from subsurface and thus different physical models
can be applied for those two regions. Subsurface rolling
contact fatigue can be treated in the usual way following the
classic, dynamic capacity model of Lundberg and Palmgren
(Ref.10), while treatment of the surface requires more advanced
tribological models that address the complex physical interactions occurring in highly stressed, concentrated
Hertzian contacts (such as lubrication, friction, wear, fatigue
or running-in).
This enables SKF to reflect, in its bearing life predictions,
more customized designs with specific features that can impact
the field performance of bearing applications. Examples
of this are bearings with specific heat treatment, advanced
microgeometry or of a particular design or quality.
Customers can take advantage of the unique features of
SKF bearings that are available in the product catalogue and
use them in rating life calculations. At the end of the day, customers
will be able to better utilize the features and quality
of SKF products that can’t be represented simply by a single
“sub-surface” dynamic load rating (C), as is done today
(Ref.11).
The ability of this new approach to deal specifically with
the degradation mechanisms and tribology of the raceway
surface will enable the use of a more advanced version of the
GBLM in bearing product development.
SKF engineers will use the GBLM to develop improved
bearing designs targeting special applications or particular
field performance requirements. In short, the GBLM represents
a modern and flexible bearing performance rating tool,
one able to incorporate new knowledge and technologies as
they are developed.