## 19 Jul 2019 Large Deformation

Large deformation, or geometric non-linearity, is one of the three non-linear behaviours in structural analysis, see:

In linear analysis, the equilibrium of forces (and moments) is established on the undeformed structure. That means, although one of the results of the FEA are deformations, the calculation has actually ignored them in the first place. This won’t affect the stress and deformation results noticeably if the deformations are small.

This does however not mean small in absolute terms, but rather if the correlation between action and reaction is affected by the deformation.

For an object (weight = action) suspended by a vertical rope, it doesn’t make a difference how much the rope is extended, as the rope force (reaction) will always be in line (but opposite direction) with the weight force, no matter how large the deflection is. In this case, considering geometric non-linearity is not required.

A horizontal rope on the other hand can only support a weight once the rope has deflected. Hence in this case, even if the weight and consequently the deflection might be very small in absolute terms, geometric non-linearity has to be set.

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