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I am a user of Mathematica as a tool for calculation in Structural Mechanics. I had a problem recently in the integration of expressions a bit long, and honestly I do not understand what might be causing the slowdown.

I want to just evaluate this:

This is for the Raileygh-Ritz method for rectangular plates. Then, i use the following code:

U=(1/2)*D1*Integrate[((D[W,{x,2}]+D[W,{y,2}])^2-2*(1-v)*(D[W,{x,2}]*D[W,{y,2}]-(D[W,x,y]^2))), {x, -a, a}, {y, 0, b}]

, were W is function of x and y

The problem is that the program continues running without answering over several minutes.

Anyone have any solution or advise that could make my process more agile?

Thank you in advance!

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# W. Mathematica 8 stays running and does not evaluate

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