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Implementing Tangent stiffness for Ogden Model in UMAT

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(@Thomas M. Moore)
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Joined: 8 years ago


I have derived the stress and Tangent stiffness expressions for Ogden material law. The derived expressions comprises of Eigen projections in tensorial notation that are obtained while differentiating eigenvalues (principal stretches). e.g. Stress S = f(lambda) N1(*)N1 + ..N2(*)N2... Tangent Stiffness C = g(lambda) N1(*)N1(*)N1(*)N1 + ... N1(*)N1(*)N2(*)N2 and so on.

I am facing difficulty while writing these expressions in UMAT. Is there any other way to get the expressions in some form other than in eigen projections one? Also how to implement tangent C as described in above example?

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