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Strain equation inconsistency ?

Posted Apr 5, 2011, 10:30 a.m. EDT Materials, Structural Mechanics Version 3.5a, Version 4.0, Version 4.0a, Version 4.1 0 Replies

Mazyar Amin
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Hi,

I was checking the strain-displacement equations that are used in COMSOL and are available in Equation Systems. If someone can give me a hint to understand the following inconsistency I'd appreciate:

From solid mechanic books we have:

e_ij = 0.5 ( u_i,j + u_j,i - u_k,i * u_k,j )

where e (epsilon) is strain and _ij denoted the index of the strain matrix and u_i,j denotes ( du_i/dx_j ).

By assuming that i=j=1 this will result:

e_11= u_1,1 - 0.5 { (u_1,1)^2 + (u_2,1)^2 + (u_3,1)^2 }

while the equation used in COMSOL has + before 0.5 rather -, in the last equation. I checked this in structural mechanics mode for a solid (_smsld).

Am I missing something?

Thanks.
Manuel
0 Replies Last Post Apr 5, 2011, 10:30 a.m. EDT
COMSOL Moderator

Hello Mazyar Amin

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