An OEM or a research interview is designed to test the ability of the candidate to solve a problem by applying physics-driven thinking skills. Unless the interviews are for people who would develop mechanical methods/mathematical models for high-end research interviews mostly check fundamentals, application and thinking skills.
Analysis: It is easy to visualise that when bolt has clearance it does not take any load. It is the friction available between wall and the bracket and the pre-load that go to constitute the balancing force for weight
If there are N bolts and if the preload is P then we have
The shear correction factor is used to account for the parabolic variation of shear stress the cross-section of the beam or shaft. When we take average shear stress, it is load by actual cross-section area, where we assume constant shear stress across the depth. This does not account for shear stress variation and hence the area is corrected by these factors.
The General formula for shear stress variation is given by
Let us find the Average shear strain energy.
The load developed by the constraint of the growth, beyond the cold clearance, contributes to the compressive buckling load. Hence, net growth beyond cold clearance must be computed. Elasticity of the shaft makes the situation worse.
Observation: For assessing the growth of the blade, the centrifugal load is considered without the shaft’s elastic deflection.
Hence, the blade is likely to buckle if centrifugal growth +Thermal growth +elastic deflection of the shaft > cold clearance.
Note: The shaft mass is neglected for the above calculation