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: Whenever we need to evaluate the stress concentration factor, we need to relate it to standard stress state, uniaxial, biaxial, either with only tensile or combination of tensile and compressive stress-state.
The current stress state is pure shear and hence equivalent to a biaxial stress state with equal compression and tension
Here we compute stress concentration due to tensile stress state and superpose it with compressive stress state. That is the principle of superposition
For the current loading 𝝈=𝝉, 𝒕𝒐𝒓𝒔𝒊𝒐𝒏𝒂𝒍 𝒔𝒉𝒆𝒂𝒓 𝒔𝒕𝒓𝒆𝒔𝒔
It is obvious that maximum stress is 4 times that of the applied torsional stress. Hence maximum stress concentration factor is 4.
Observation: In order to analyse the effect on component or joint we need to first list various possible modes of strength and structural failures.
Combined Creep LCF damage is more than the sum of individual damages
For thermal fatigue one should not use mechanical S-N curve
Observation: In order to understand the failures we should not only consider the loads but also it’s assembly and operating conditions.
Comprehension: Generally piston ring is mounted onto an external square grove of the tube. The pressure differential exists in one direction (from right to left). As the tube spins the piston ring also expands centrifugally.
ISSUE one (Failure mode)
As the piston ring grows due to centrifugal load and due to temperature and since it is stopped by the outer ring the ring may fail by buckling
ISSUE two Failure mode and reparability)
Due to vibration, the ring may continuously rub the sealing tube and the wall thickness of the outer tube is critical and must be carefully designed. If it becomes too thin reparability is affected
Let us assume that P is the critical external pressure seen by the ring. If the growth of the ring is restricted, then we have:
A tube is inside a tube the air should not leak across the out springing piston ring works when the engine is running as tube is also rotating and has centrifugal load it seals but when engine is shut down piston ring slides to the middle