Vonmises Stress Vs Maximum Principle Stress

In summary, Von Mises stress theory suggests that failure will occur when the maximum principal stress in a system reaches the value of the maximum stress at elastic limit in simple tension. The theory is approximately correct for cast iron and brittle materials generally. More information on Von Mises stress can be found at http://en.wikipedia.org/wiki/Von_Mises_stress.
  • #1
Chandrakiran
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Hello All,

Can anyone let me know the difference between Vonmises Stress criterion and Maximum Principle Stress criterion ?? And for what kind of materials " Brittle / Ductile " can they be used and why ??

Thanks in advance for your time.
 
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  • #2
Maximum Principle Stress Theory - According to this theory failure will occur when the maximum principal stress in a system reaches the value of the maximum stress at elastic limit in simple tension. This theory is approximately correct for cast iron and brittle materials generally.

Source: http://www.roymech.co.uk/Useful_Tables/Mechanics/stress.html


Von Mises Stress (Distortion Energy Theory) - This theory proposes that the total strain energy can be separated into two components: the volumetric (hydrostatic) strain energy and the shape (distortion or shear) strain energy. It is proposed that yield occurs when the distortion component exceeds that at the yield point for a simple tensile test.

Source: http://en.wikipedia.org/wiki/Yield_(engineering [Broken])

More information on Von Mises Stress can be found http://en.wikipedia.org/wiki/Von_Mises_stress" [Broken].


General information on solid mechanics can be found http://en.wikibooks.org/wiki/Solid_Mechanics" [Broken].

CS
 
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  • #3
HI,

Thank you very much for very useful information and your precious time.

Chandra.
 
  • #4
stewartcs said:
Maximum Principle Stress Theory - According to this theory failure will occur when the maximum principal stress in a system reaches the value of the maximum stress at elastic limit in simple tension. This theory is approximately correct for cast iron and brittle materials generally.

Source: http://www.roymech.co.uk/Useful_Tables/Mechanics/stress.html


Von Mises Stress (Distortion Energy Theory) - This theory proposes that the total strain energy can be separated into two components: the volumetric (hydrostatic) strain energy and the shape (distortion or shear) strain energy. It is proposed that yield occurs when the distortion component exceeds that at the yield point for a simple tensile test.

Source: http://en.wikipedia.org/wiki/Yield_(engineering [Broken])

More information on Von Mises Stress can be found http://en.wikipedia.org/wiki/Von_Mises_stress" [Broken].


General information on solid mechanics can be found http://en.wikibooks.org/wiki/Solid_Mechanics" [Broken].

CS
Hi all,

with regards to the max. principal stress vs von mises stress, does a material yield or fail if the von mises is greater than the max. principal stress or visa versa?

secondly, how is the von mises related to compressive strength (or minimun principal stress)?

your help will be greatly appreciated

regards

Tach
 
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  • #5
Tach159 said:
Hi all,

with regards to the max. principal stress vs von mises stress, does a material yield or fail if the von mises is greater than the max. principal stress or visa versa?

secondly, how is the von mises related to compressive strength (or minimun principal stress)?

your help will be greatly appreciated

regards

Tach

The beauty of Von Mises stress is that in the real world "everything" fails by shear. That's why it has emerged as the favorite failure theory. Having said that, the world of material failure is highly stochastic - subject to statistical variation. So as good as the theory is, you still need significant factors of safety if you don't want your project to come crashing down.

You find Von Mises stress from the principle stresses by using a big ol gnarly equation or three. It is always a smaller value than maximum principle stress (by definition) BUT it is aligned in the direction that has to support the maximum shear load. This can be very helpful in design.

hth (and i hope that I'm not too rusty on this subject)
 
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Likes gedw
  • #6
This is an old thread.

What is the interest in revival?
 
  • #7
A question was asked, I assumed it was cool to answer it. Silly me.

It would have been better to start a new thread?
 
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Likes gedw

1. What is the difference between Vonmises stress and maximum principle stress?

Vonmises stress and maximum principle stress are two different ways of measuring the stress on a material. Vonmises stress takes into account both the normal and shear stresses on a material, while maximum principle stress only considers the maximum normal stress. This means that Vonmises stress can more accurately predict when a material will fail under complex loading conditions.

2. Which one is more appropriate for design and analysis?

Vonmises stress is generally considered more appropriate for design and analysis, as it takes into account a wider range of stress components. Maximum principle stress is often used as a conservative estimate for failure, but may not accurately reflect the true stress on a material.

3. How are these two stress measures related?

Vonmises stress is derived from the maximum principle stress, and is calculated using a formula that takes into account the normal and shear stresses. In certain loading conditions, the value of Vonmises stress may be equal to the maximum principle stress, but this is not always the case.

4. Can Vonmises stress ever be greater than maximum principle stress?

Yes, it is possible for the Vonmises stress to be greater than the maximum principle stress. This can occur in materials that are subject to complex loading conditions, where the shear stresses play a significant role in the overall stress on the material.

5. In what scenarios would it be more appropriate to use maximum principle stress?

Maximum principle stress is often used in situations where the material is subject to simple loading conditions, such as tension or compression. It may also be used as a conservative estimate for failure in materials that are prone to brittle fracture.

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