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English Wikipedia in the Poisson's ratio article gives an equation for large deformation: $$ \frac{\Delta d}{d}=-1+\frac{1}{\left(1+\dfrac{\Delta L}{L}\right)^\nu} $$

I couldn't find any reference for this equation. Could someone help? I need it in my thesis, and I'd like to reference some other source than Wikipedia. Every other publication I've seen so far gives the approximate (linear) equation.

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up vote 3 down vote accepted

Start with differential form of Poisson's ratio:

$$\frac{\text{d} x}{x}=- \nu \frac{\text{d} l}{l}$$ $$\int_{x_0}^{x_0+\Delta x} \frac{\text{d} x}{x}=- \nu \int_{l_0}^{l_0+\Delta l} \frac{\text{d} l}{l}$$ $$\ln \frac{x_0+\Delta x}{x_0}=- \nu \ln \frac{l_0+\Delta l}{l_0}$$ $$1 + \frac{\Delta x}{x_0}=\left(1+\dfrac{\Delta l}{l_0}\right)^{-\nu}$$

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Plain and beautiful. Thanks! –  texnic May 9 '12 at 15:31

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