Plane Stress/Strain

[peglor]

Hi all,

I'm wondering what are there guidelines to use in order to decide whether a 2D model should be run as a plane stress or a plane strain model. I have results from FE runs using both options and I'm wondering which is more correct.

The model is a socket in contact with a nut. The nut is about 20mm across the flats and the model is assumed to be unit depth, though in reality, the nut would be about 10mm high.

 

[corus]

Both your runs are correct as an approximation in that the 20 thick nut is neither plane stress nor plane strain but somewhere inbetween. The nut can not be considered as a thin plate and cannot be considered to have infinite thickness, though judgement would favour that a thin plate is closer to reality than infintely thick. The true test is to compare your results with a 3D model if you're not sure and use the model that most closely matches the results of the 3D model. The results from your two 2D runs should give you an upper and lower bound on the true answer. Choose the one that gives you the worst results if you want to be conservative in your approach to future analyses of the nut.