3.5.6. AE Testing of Bearings

In one of the bearings, the lubricant dried, which led to intense friction and a rattling in the audible range. AE sensors also recorded signals with an amplitude of about 100 dBAE and a duration of more than 100,000 μs (Figure 20).

**Figure 20.** AE signal recorded on the bearing housing. Drying of lubricant.

When defects are formed, for example, fatigue cracking or crack, a significant change in the nature of the AE signal flow occurs such as the activity grows, amplitude trends appear, and, most importantly, there is a periodicity of appearance due to the fact that acoustic signals at this stage occur during periodic collision of the bearing roller with place of damage [23].

A moderately active source of AE was detected on the bearing of one of the supports (Figure 21a), which, due to a low characteristic amplitude level, did not undergo the confirmation procedure. A more powerful periodic source of AE (about 100 dBAE), found on another support (Figure 21b), was a crack in the outer ring of the bearing.

**Figure 21.** Periodic AE signals registered on the bearing housing. (**a**) Moderately active source of AE; (**b**) external ring crack.
