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How Load-Carrying Capacity Affects Bearing Service Life
Bearings, much like humans, face stress in their daily operations. It's crucial to choose a bearing that can handle the pressure—essentially ensuring it doesn't get "stressed out." In simpler terms, the bearing’s load capacity must be sufficient for the actual load it will endure throughout its service life.
If the applied load exceeds the bearing's capacity, it can lead to accelerated wear or even permanent deformation, significantly shortening its lifespan. When selecting a bearing, two main types of stresses should be considered: static and dynamic.
Static stress refers to the condition of the bearing rather than the nature of the load itself. It occurs when a load—whether constant or variable—is applied to a bearing that is either stationary or moving very slowly. If the load is too heavy, it can cause plastic deformation on the rolling surfaces or even flatten the rolling elements, leading to premature and potentially catastrophic failure.
Dynamic stress, on the other hand, relates to the motion of the bearing. It happens when a load is applied to a rotating bearing. If the load is too high for the bearing’s capacity, it can result in early fatigue, causing cracks and flaking in weak areas. This ultimately leads to failure due to material fatigue, which is essentially the end of the bearing's useful life.
There are several theories explaining what causes fatigue-related failures. The maximum shear stress theory suggests that the primary cause is the highest shear stress within the bearing. The distortion theory claims that fatigue results from stresses across a region, not just at one point. The alternating shear stress theory, however, states that orthogonal stresses within the bearing are responsible for material fatigue.
While all three theories have some supporting evidence, the alternating shear stress theory is most commonly used in calculating the fatigue life of rolling bearings. Fatigue life, or rating life, is defined as the number of revolutions or hours a bearing can operate at a constant speed before 90% of a group of identical bearings show the first signs of material fatigue. Typically, the rating life decreases as the load increases.
At Emerson Bearing, our team of experts is here to help you select the right bearings for your application, ensuring they don’t get “stressed out.†We provide comprehensive support for all your bearing needs. Contact us today or explore our **Catalog** and **Technical Toolbox** pages for more detailed information on how we can assist you.