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Thin plate theory...
I have a small doubt in the assumptions made in thin plate theory.
We make some of the following assumptions in thin plate theory (Kirchoff's classical plate theory) (KCPT).
 The normal stress (out of plane=> sigma(z)) is zero. and
 The vertical deflection 'w' is not a function of 'z' => dw/dz = 0
Now there are three stress components sigma(x), sigma(y) and sigma(xy). The other three stress components sigma(z), sigma(xz) and sigma(yz). This is like a plane stress.
But, from the second assumption ez=0 (strain in z-direction) and from the above exz=0 and eyz=0.
Then, this leads to plane strain.
From the constitutive equation for 'ez' => sigma(x)+sigma(y)=0
But, this doesn't happen.....I am looking for explanations ...
Thanks in advance.