Mechanical Engineering - Machine Design - Discussion

Discussion Forum : Machine Design - Section 4 (Q.No. 50)
50.
If a shaft made from ductile material is subjected to combined bending and twisting moment, calculations based on which one of the following failure theories will give the most conservative value?
Maximum principal stress theory
Maximum shear stress theory
Maximum strain energy theory
Maximum distortion energy theory
Answer: Option
Explanation:
No answer description is available. Let's discuss.
Discussion:
21 comments Page 1 of 3.

Atanu Pal said:   2 years ago
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).
(1)

Kuldeep singh said:   8 years ago
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.

Mahesh said:   1 year ago
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.
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Hardik said:   1 decade ago
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.
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Parry said:   7 years ago
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.
(1)

Dhanendra thakre said:   9 years ago
In above question there is two-term is used first is , for ductile and second is conservative .
For ductile material two possibilities MSST and MDET. But MSST conservative is most because it has hexagonal form and MDET have an ellipse in charm curve.

Rajkotha said:   4 years ago
In question, there are two points that need to be noted.

1. Ductile. 2. Most conservative.

Hence for ductile with the most conservative maximum principal stress theory is to be considered.

Deekshit said:   9 years ago
In the above 2 conversations, they missed one point that is in question.

It is asked to find most conservative value so the answer is maximum normal stress theory.

Anonymous said:   7 years ago
The principle stress theory is for brittle material.

The principle shear stress theory is specifically for a ductile material.

So, the correct option is B.

SATYANDRA said:   1 decade ago
Maximum shear stress theory is answer. Maximum principle stress theory is known as Rankine's theory and maximum normal stress theory.
(1)


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