Hi all, Model is with CPS4 elements and the vonmises stress at the integration points(int pts) and nodes(0% averaging) from Abaqus are,

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int pts (S'): 3.77465, 3.61543, 3.57685, 3.73598

nodes(S) : 3.85078, 3.57542, 3.5084, 3.78352

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but i was interested to find the way how the extrapolation is done in abaqus, so i started with shape functions and the gauss points and obtained the extrapolated stress as below,

4 Gauss point locations (g,h) are (+/- 0.5773)

[S]=[N][S'] (N shape function), N1=1/4(1-g)(1-h); N2=1/4(1+g)(1-h); N3=1/4(1+g)(1+h); N4=1/4(1-g)(1+h)

S             =                                                                                      N                                                                                             *          S'

the vonmises values at nodes are,

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extrapolation by calculation : 3.713414143, 3.66033907, 3.691089952, 3.638066836

extrapolation by Abaqus : 3.85078, 3.57542, 3.5084, 3.78352

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the deviation is too much, whats the reason for this deviation? any thing wrong with hand calculation?