EC5 - Decompose Stiffness in Position

ε (z) = \{\begin{matrix} ε_{x} \\ ε_{y} \\ γ_{x y} \end{matrix}\} = \{\begin{matrix} \frac{\partial u}{\partial x} \\ \frac{\partial v}{\partial y} \\ \frac{\partial u}{\partial y} + \frac{\partial v}{\partial x} \end{matrix}\} + z \{\begin{matrix} \frac{\partial φ_{y}}{\partial x} \\ - \frac{\partial φ_{x}}{\partial y} \\ \frac{\partial φ_{y}}{\partial y} - \frac{\partial φ_{x}}{\partial x} \end{matrix}\}

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