Page 434 - Failure Analysis Case Studies II

418

Fig. 3 P1 the new one.

The rolling elements, Cr-steel balls, also experienced severe deformation and wear; see Fig. 4d-i.
One of these balls, which was stressed to a relatively small extent was sectioned to study the locations
where stresses were overbearing. The etched sample in Fig. 4d-ii shows a band of the stressed region
which is -4 mm wide and generated while the ball was rolling.
To summarize the above observations, the inner and one of the outer races of the retrieved
bearing were heavily deformed from one side. The off-center extensive deformation indicates high
stresses operating in these areas prior to the failure. The inner and outer races put together with the
cage in Fig. 3a show the probably configuration in which the cage broke and was trapped between
the balls and the races. The balls shifted towards one side and severely deformed the races. The
function of the bearing was impaired resulting in the air crash. The observations concerning the
deformation and smearing of the components are sketched in Fig. 4e to show the possible position
and condition of the bearing components just before the accident.

2.2. Material of CMB components
The chemical analysis of different parts of the bearing was carried out using energy dispersive X-
ray analysis (EDX), atomic absorption spectroscopy (AAS) and carbon/sulphur (C/S) analyzer.
The cage is fabricated from a Cu-A1 alloy; its chemical composition is summarized in Table 1.