Investigation approach
Preassessment of damaged part
The damage assessment typically starts with the visual inspection of the failed part, e. g. a failed brass cage, and thus the determination of the visible damage characteristics and traces of usage. Based on that, the further approach will be defined.
Investigation of fracture faces
Using the example of this cylindrical roller bearing, a fracture of the brass cage was detected and its fracture faces could be further investigated. As depicted, the right side ring is completely broken which resulted in hammered fracture faces. However, the left side ring could be opened manually to make the crack growth visible.
Determination of the damage mechanism
The investigation by scanned electron microscopy finally led to a broad comprehension of the damage mechanism. In the current case, the fracture could be classified as fatigue failure while the crack origin was detected too. Furthermore, the orientation of the crack plane and the size of the residual fracture face provided useful information on the loadcase that finally lead to failure.
Definition of damage hypothesis
The determination of the damage mechanism is necessary for the definition of the damage hypothesis. However, in this context any further and possibly relevant information is used too. This means especially information on:
- operation conditions
- executed and recommended maintenance activities
- specification
- observations by e. g. operation personnel
- traces of usage of other parts of the same technical system
Simulation
If the information which is available by now does not lead to a unique description of the relevant interrelationships, numerical simulations may help to check the plausibility of different theories. In the related example, both axial impacts and several vibration modes were simulated.
Comparison of simulation and observation
The comparison between simulation results and observations leads finally to the determination of the load case for which not only the position of the crack origin fits to the area of maximum calculative stress amplitudes but also the total load level corresponds to the shape of the fracture face. In the best case, the total amount possible theories can be reduced to one by this approach.
Final assessment and definition of valid counteractions
If the executed investigations led to a clear result, the related scenario will be described and explained in a detailed report. After that, the gathered deep comprehension of the relevant issues will be used to define valid counteractions in order to prevent further damages of the same kind.
