What would you expect to observe in a normal bearing with a defect on the inner race?

When a defect is present on the inner race of a bearing, it impacts the vibration signal captured. In a healthy bearing, the vibration signals primarily consist of periodic impulses due to the rolling elements passing over smooth surfaces. However, when there is a defect, such as a crack or dent on the inner race, it generates impulse signals that are associated with the rotation of the shaft.

The correct answer illustrates the presence of a non-synchronous peak with shaft rate sidebands, which corresponds to the rotation frequency of the shaft. This pattern occurs because the defect produces multiple impacts as the rolling elements traverse over the imperfection, leading to the generation of sidebands around the fundamental frequency. The sidebands represent modulation effects from the rotational frequency, reflecting how often the rolling elements hit the defect as they rotate.

This phenomenon helps in diagnosing the specific type of bearing fault while distinguishing it from other issues such as those related to shaft misalignment or unbalance, which would show different characteristics in the vibration spectrum. Observing these peaks and sidebands can also aid in determining the severity of the defect and its potential impact on equipment performance.