i am trying to create contact set between roller and surface , the problem is that when i choose automatic contact set with touching faces it not detected , but when i choose with non touching faces it is detected.what should i do in such case , what should i select in adavance tab option .i can see little clearance between roller and surface . please need guidance
thank you
In a real roller situation you only have a line contact (or point in the case of a ball on a flat surface). FEA does not like this. Remember, pressure = force/area; as the area goes to zero the pressure will go to infinity. In cases like you describe above what I have used (fairly) successfully in static analysis is to make the diameter of the roller slightly larger and shear off the bottom so you have a small rectangle that transfers force. You can actually tune this to mimic Hertzian stress to some degree. Doing that will allow the transfer of forces w/out causing a stress concentration or singularity.
It’s better to avoid any gaps, define contact pairs manually and use displacement control whenever possible.
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THANK YOU FOR reply , exactly i am trying my best to avoid gaps , i am going to use contact set manually , how can i control displacement
Displacement control simply means that you apply prescribed displacement (for example make some nodes move 5 mm downwards) instead of force.
Can I use displacement and force at same time?
The structure involve static study with force ranges
If I use displacemt can I find force that required to produces stress at mentioned displacement?
Thank you
Not at the same time but in many cases they can be used interchangeably. It depends if you can estimate equivalent force or displacement. Generally the rule is to use the type of control that occurs in real life for the structure. However, in some cases displacement control might be necessary to overcome convergence issues.
This article describes the details: https://enterfea.com/changing-active-forces-for-enforced-deformations/
It is always a good idea to use Hertzian contact calculations (from Roark’s or online calculators) to get a good idea of what stresses to expect with the given parameters BEFORE you even start an FEA run.