Reply To: How to calculate eigen frequencies using analytical approach?

[peteroznewman]

Hooke's Law describes a linear relationship so is valid on linear models. Stiffness doesn't change in linear models.
Once you talk about nonlinear effects, then Hooke's law only applies during the initial linear elastic deformation, and not when the large deflection starts. If you have a hyperelastic material model, Hooke's law does not apply because the force-extension data is not linear.