Hello all, me again. I have done well, I think, to get this far without pestering you guys, but here goes...
I am trying to model the compression of a rubber o-ring in a slightly undersized groove. The attached models are revolved through 1deg, so are slightly wedged (p0ssibly an unnecessary compication, but ultimately I will do a bigger revolve for better visual impact). I think this allows me to get away with frictionless restraints.
I want to apply a force of around 30N, which I think will approximate atmospheric pressure. Up to 2N, applied slowly, the CONTACT conditions hold, but at a fraction over 2N the o-ring crashes though its base CONTACT (force.liml). If I blindly beef up K to 5000, The CONTACT holds but many elements fail (force2.liml). If I try K 2500, elements fail even before the o-ring hits the base CONTACT.
If I take away the force and just use a displacement over time of the nodes at the base of the window, the o-ring compresses fine. It seems to me that with the force applied, the o-ring suddenly squeezes into the groove, past the radii, then hurtles friction-free downwards, causing failure of the model. I tried some different friction values to make it a bit more controlled, but it was taking an age to converge, so I figured things were not right and abandoned - I can't spend that much time in the trial-and-error stage.
I will now try to engage the o-ring with the walls and base of the groove by using a timed displacement, which I know I can do. Once partially compressed, I will try to introduce a timed force. I am not sure how I will time it, whether to introduce the force on the next time step after the last displacement, or whether to overlap them. Or would I be better off increasing the mesh resolution of the o-ring at this stage? Or are there some better settings that will allow the force only approach to work?
With rubber being incompressible (Poisson ratio close to 0.5), I am not sure how well this model copes (not well, I think) when there is nowhere to expand into under compression - presumably the modulus should increase at this stage, which this model does not have. I suspect this is why we have elements deforming. I made the elements of the o-ring longer in the vertical (y), which improved things, but I am at the stage now where input from you guys and girls could save me a lot of time and experimentation.
Thanks for reading, please ask if any more info needed.
Comments
Thanks again, and for the link Sergio.
D
I copied the whole block of *BOUNDARY text and pasted in the custom step box, e.g.
This solved with no indicated error but did not have the intended effect. I will carry on trying to work it out. Any suggestions?
Thanks
I will certainly take a look at the force approach too. Will let you know.