Discussion Forum

When the Force linear strain check box is selected, that material is treated as geometrically linear in an otherwise geometrically nonlinear analysis. You can use it, for example, to override the geometrically nonlinear formulation which is forced by some features, such as Contact.
It is only the switch back to engineering strains that is affected. Other properties of a geometrically nonlinear formulation, such as the split between material and spatial frames are still kept. The check box has only effect if the current study step is geometrically nonlinear.

Dear Dr Sönnerlind, many thanks for your reply. Sorry I still don't get it completely. Does switching on/off 'force linear strain' not affect the defined variables in the 'equation view'? If it takes effect depending on the study step, the effect/difference should be reflected from the defined variables, otherwise there's no difference to the equation solving.

Yes, it takes effect in Equation View. If you look at the expressions for the strain variables you should see it, given that Show equation view assuming points the the intended study step.

Many thanks, but as far as I see under 'linear elastic material', when checking or not checking 'force linear strains', the x strain is always solid.el11=solid.eXX=uX.

Difficult to tell, it definitely changes on my screen (as long as I am pointing to a geometrically nonlinear study step).

Dear Dr Sönnerlind, many thanks for your reply. Yes I can see how this can take effect. However what's the difference between ticking 'force linear strains' under the physics setting and unticking 'include geometric nonlinearity' under the study setting?

Force linear strains only has a meaning if Include geometric nonlinearity is selected. It overides that setting.

By the way: In version 6.0, soon to be released, the Force linear strains checkbox has been renamed to Geometrically linear formulation.

Then if one ticks both 'Include geometric nonlinearity' and 'Force linear strains', is that equivalent to unticking both?

Please look at my first answer.

Thank you Henrik.