Meet the Presenter
This article is based on a webinar presented by STLE Education on March 6, 2024. Rolling Element Bearings - Beyond Basic Life and Load Rating is available at www.stle.org: $39 for STLE members, $59 for all others.
STLE member Dr. Hannes Grillenberger is a key expert on rolling bearing fundamentals at the motion technology company Schaeffler. He focuses on rolling element bearing noise. He joined Schaeffler in 2012 after receiving his doctorate in physics at the University of Erlangen-Nuremberg, Germany. Since joining Schaeffler, Dr. Grillenberger has worked on simulation methods for rolling element bearing friction, cage strength and noise, with noise being his primary area of focus for the past eight-plus years. He holds several patents and has received multiple conference awards. He frequently publishes technical papers in journals and presents at industry conferences. Since 2024 he has been the product manager for Schaeffler’s bearing and transmission simulation tools.
Dr. Grillenberger is currently a member of STLE’s Board of Directors, the STLE Rolling Element Bearing Technical Committee as well as the STLE Annual Meeting Planning Committee. At STLE’s annual meetings, he is also responsible for lecturing on the topic of dynamic assessment of rolling bearings. You can reach him at hannes.grillenberger@schaeffler.com.
Hannes Grillenberger
KEY CONCEPTS
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Excellent bearing design needs to go beyond ISO life ratings; they fail to account for complex factors such as variable dynamic loads, thermal stresses and material-specific performance, all of which are critical for accurate bearing life prediction.
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Advanced simulation tools are also essential for reliable bearing design. They allow engineers to model real-world conditions including load distribution, friction, lubrication and transient dynamics.
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Collaboration and validation are key to trust and accuracy. Partnerships with independent certification bodies ensure trust in methods and protect intellectual property rights.
Understanding bearing performance has moved far beyond relying on static or dynamic load ratings. Now advanced analysis tools and simulation models are transforming the way engineers design, evaluate and optimize bearing systems. In essence, for an environment where machinery is more complex, lightweight and efficiency-optimized; demands are higher; and the detection of failures and their cause is less clear, excellent bearing design needs to go beyond ISO life ratings.
This article is based on an STLE webinar titled Rolling Element Bearings - Beyond Basic Life and Load Rating presented by STLE member Hannes Grillenberger with Schaeffler. See Meet the Presenter for more information.
Limitations of ISO standard life ratings
Because of the drive toward sustainability, friction, thermal, electrical, noise and dynamics parameters affecting rolling element bearings receive the most design consideration. However, since bearings are implemented in systems, the loads and speeds transmitted to the bearings also need to be taken into consideration.
Traditional bearing life calculations, such as those defined in ISO 281, have long provided a basic framework for engineers and still do. ISO 281:2007 specifies methods of calculating the basic dynamic load rating of rolling bearings within the standard ISO size ranges in accordance with manufacturing practice and conventional design. However, these models fail to account for the demands of modern machinery—such as variable dynamic loads, surface fatigue mechanisms and thermally induced stress. Classic ISO-related calculations are also limited when considering surface-initiated fatigue or elastohydrodynamic (EHL) contact behavior in mixed friction.
In addition, standard bearing life ratings don’t factor in today’s high-performance materials or failure modes that often go undetected. Advanced bearing engineering requires tools that can simulate load distribution, contact pressure, friction, thermal effects, fatigue and more.
Simplified equations risk underestimating or misdiagnosing bearing performance, especially in applications where the operating environment is far from ideal. When rolling element contacts involve complex behaviors such as EHL or surface-initiated fatigue, engineers must move beyond classic models and apply advanced simulation strategies.
Advanced simulation tools for real-world applications
The optimal bearing design for each application begins in the conceptualization phase of the overall system
(see Factors Affecting Bearing Application Life). If the bearing load and operating conditions are taken into account in the initial design and dimensioning of the components, subsequent design changes, which often involve considerable time expenditures and costs, can be effectively prevented.
Factors affecting bearing application life
Factors affecting bearing application life that are candidates for simulation include:
• Lubricant flow
• Dynamic wear evolution
• CO₂ emissions
• Hardening profile
• Transient bearing dynamics
• Gear assessment (quasi-static, dynamic)
• Noise, velocity, harshness (NVH)
• Cage rattling/instability
• Friction/power loss
• Temperature distribution
• Rating life ISO 281
• Surface initiated damages (e.g., wear, micro-pitting)
• Advanced rolling contact fatigue (e.g., different materials)
• Cage fracture/failure
• Plastic deformation (overload)
• Ring creeping
• False brinelling
Bearing simulation tools offered by companies generally fall into four categories.
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Load analysis: for static and dynamic loads, integrating housing and shaft elasticity in order to model force feedback and contact behavior.
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Transient half-space models: used in contact simulation to analyze short-term dynamic effects such as thermal gradients and contact evolution.
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3D simulation tools: for complex systems such as crankshafts and gearboxes where dynamic load changes are highly nonlinear and multi-axial.
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Friction and thermal modeling: including local discretization of contact areas to evaluate friction energy distribution and temperature rise.
The key to relevant bearing simulation is not which tool is used but ensuring it aligns with the application and level of detail required.
Factoring in material performance
One important advancement is the inclusion of material-specific life factors. For instance, high-grade steels or special heat treatments can extend bearing life well beyond what standard life equations predict only by changing the material. However, these enhancements must be certified—either internally or via trusted third parties.
Collaboration between bearing manufacturers and certification bodies can validate methods for calculating enhanced life factors. However, transparency in deriving these factors is essential for customer trust and consistent engineering results.
To ensure credibility, bearing manufacturers partner with independent certification bodies such as Technischer Überwachungsverein (German for Technical Inspection Association, TÜV) and Det Norske Veritas (Norwegian for The Norwegian Truth, DNV). These Europe-based organizations verify the accuracy of the internal calculations and simulations used to derive extended life factors. Transparency in this process helps customers trust the data they rely on for design decisions.
Friction and contact energy modeling
Methods for calculating local friction energy may evaluate the pressure and relative sliding velocity in each contact area, making them ideal for systems such as needle bearings or hybrid gear contacts where sliding is significant. This methodology enables precise prediction of:
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Load distribution among rolling elements
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Localized heat generation
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EHL film thickness
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Electrical resistance across contacts
These detailed outputs not only aid in selecting the right bearing but also help optimize lubrication strategies to reduce wear and extend service life.
Oil flow and lubrication modeling
High-speed and thermally sensitive applications demand a clear understanding of how lubricants behave under certain conditions. Particle-based simulation models—developed in collaboration with external research partners—study oil flow dynamics. These simulations are faster than conventional mesh-based computational fluid dynamics (CFD) and are better suited for analyzing how design changes affect lubrication and heat dissipation. This work allows engineers to predict bearing life and especially friction and contact lubrication more accurately, based on how well the lubricant performs under real-world conditions.
Expanding into hydrodynamic bearings
Although the simulation and modeling focus is primarily on rolling element bearings, there is growing attention to hydrodynamic (sliding) bearings. These bearings require different modeling approaches, but the principles remain the same; accurate characterization of materials, contact calculation fluid behavior and thermal effects are essential to predict system performance and reliability.
In the case of hydrodynamic bearings, the mechanical system interaction is as important as for rolling bearings. The mechanical parts need to be compliant. The clearance of these bearings is within micrometers. The bearings are in dimensions of 500 mm—by elastic deformation of the structure, the bearing might be loaded differently. It is also crucial to integrate this interaction of the bearing stiffness (changes with load) and the elastic system.
Partnering for engineering success
In today’s demanding and complex machinery environments, traditional ISO bearing life ratings are no longer sufficient. The future of bearing design is not just about better steel—it’s about better insight. Bearing engineering needs to incorporate advanced modeling of thermal effects, material behavior, lubrication and dynamic loads to serve the advanced performance criteria of bearings that are beyond subsurface fatigue life rating. Success hinges not just on using the right bearing but on working with bearing designers and manufacturers that can expertly leverage analytical tools, engineering expertise and real-world validation for additional benefit such as energy efficiency, low noise, electric compatibility or optimized transient behavior.
These tools provide deep insight into system-level interactions and component-level stresses, helping to prevent costly redesigns. Certified simulation methods that incorporate material enhancements and contact-level behaviors ensure both reliability and transparency. Ultimately, effective bearing design hinges on early integration of simulation into system development, collaboration with trusted partners and a shift from generic calculations to the detailed, application-specific analysis that today’s ultra-sophisticated simulation and modeling technology enable.
Jeanna Van Rensselar heads her own communication/public relations firm, Smart PR Communications, in Naperville, Ill. You can reach her at jeanna@smartprcommunications.com.