Mechanical Engineering - Machine Design - Discussion

If shaft made with the ductile material then they only follow Rankine Theory because it gives a satisfactory result for the shaft. As all knows guys Rankine theory also known as Maximum principal stress theory, therefore, option A is right here.

Thanks.

Answer is D.

When a shaft made from ductile material is subjected to combined bending and twisting moments, the theory of maximum distortion energy usually provides the most conservative estimate of failure. This theory takes into account both the normal and shear stresses to determine the critical failure condition.

Actually.
All Theories are Failure material. (Ductile/Brittle)

So
Maximum Principal stress theory Failure Brittle Material.
and Maximum shear stress Theory Failure Ductile Material.

Then;
Noted the Point;
1. Ductile Material.
2. Will Give the Most Conservative Value.

Ductile materials are no Failure which Theory (Conservative Ductile Material)

Maximum Principal Stress Theory is Ductile material Most Conservative (No failure).
Brittle Material Failure (Non-Conservative).

That's why the answer is Option ( A).

The correct answer is option B.

B is the correct answer.

Most efficient criteria for ductile material is von mises.

Principal stress theory can not be used for ductile material because, principal stress theory holds good at tension and compression and weak at shear loads. Whereas ductile materials are need to check for that shear capacity so it is recommended to use maximum distortion energy theory or maximum shear stress theory.

Maximum shear stress theory is answer. Maximum principle stress theory is known as Rankine's theory and maximum normal stress theory.

[B] is the right answer.

Answer will be option D that is the max. Distortion energy theory because this provide the best and economic design for the ductile materials. Also answer B could be correct if option D is not given because this also provide good results for ductile materials but the design is oversafe that means safe but uneconomic design.