Solid normal strains vs solid principle strains

[sigurd.naess]

Hi!

What is the difference between e.g. Solid Z-normal strain and solid principle -C strain ?

I've attached a picture of the Grid Point Strains.  

Regards
Sigurd

[Anonymous · Accepted solution]

Normal strain X, Y, Z and shear strain XY, YZ, ZX are related to the model coordinate system. Principle strain A, B, C is related to a transformed coordinate system for each node where shear strain is eliminated.

[John_Holtz · Accepted solution]

Hi Sigurd,

It looks like the difference is about 0.54E-5 😀.

• The Solid-Z Normal strain is the tension (or compression) strain in the Z direction. If you did not change the material axis orientation, then the Z direction is the global Z direction. If you changed the material orientation, then Z is in the local Z direction. See How to define the material axes in Nastran In-CAD.
• The three principal strains are not aligned to the X, Y, and Z axes except in specific situations. (The Direction Cosines give the directions; the C principal strain is toward the -Y and +Z.) The A, B, and C principal strains are the maximum, intermediate, and minimum principal strains. The principal strains can be calculated by solving a 3x3 matrix that is formed from the 6 strain tensors: X-, Y-, Z-Normal, XY-, YZ-, ZX-shear.
• For a 2-D state of stress, the Mohr's Circle can be used to visualize the difference between the normal and shear strains and the principal strains.

(Edit. Sorry @Anonymous . I either did not see your reply, or I spent a long time composing my reply. Maybe you type faster than me!)

[sigurd.naess]

Thank you both 🙂 

[Anonymous]

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@John_Holtz wrote:

... It looks like the difference is about 0.54E-5 😀. ...

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That's fun ... I had the same idea to reply this way ... but finally could resist. 😉

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@John_Holtz wrote:

... Sorry. I either did not see your reply, or I spent a long time composing my reply. Maybe you type faster than me!) ...

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No reason to say sorry. I guess I started much earlier and was still typing when you began your replay. Be sure it took longer for me to write this short post then you needed for your much larger one. 😉

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@John_Holtz wrote:

... The A, B, and C principal strains are the maximum, intermediate, and minimum principal strains. ...

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BTW: In the plot editor dialog of the post processor, what is the difference between "Solid Max. Principal Strain" and "Solid Max Prin Strain" or "Solid Min. Principal Strain" and "Solid Min Prin Strain"?

The same for "Solid Principal A Stress" and "Solid Max Prin Stress" or "Solid Principal C Stress" and "Solid Min Prin Stress"?