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: The sheet metal is subjected to both bending and axial load. Since both stresses have the axial direction these stresses could be added.
Let the area of the plate be A and plate thickness be h. The bending moment caused is, Fh and maximum stress caused is given by
The ratio of maximum stress to minimum stress
Observation: Torsional stiffness can be expressed as M/θ. Here, we consider the moment M due to axial load, and by finding the slope owing to M, torsional stiffness could be computed.
Elastic deformation of the beam is shown below
Shafts in many product lines run at very high RPMs. The question is does this high RPM, lead to significant loading causing high hoop and radial stresses?
Observation: The critical fact is if the shaft is hollow or solid. Also, the shaft being a long cylinder it falls under plane strain conditions. Therefore, the equations used for hoop and radial stresses must be those derived assuming plane strain conditions for an axisymmetric cylinder. Generally, shafts are hollow as weight consideration is very critical to performance, and of course shaft integrity is of utmost significance.
Note: Since the shaft is thin-walled same result is got even if we use, plane stress conditions!
The observation is very simple and straight forward the stress increases 4 times if speed is doubled, so is the case with radius. In the case of steam turbine shaft the radius is much higher compared to gasturbine and hence CF loading may become considerable!