Use in Structure Mech. Dynamics

[alwaysdrunk]

hello


i need your experties on MDO. i have here an assembly of two plastic parts that should slide and fit exactly to each other.the problem is, my prototype fails, it broke because maybe of too tight tolerance, I wanted to create a stress anlysis using MDO use in structure before I redesign the parts.


the green part slides downward to just exact fit, not too tight and not too loose.how do I get the loads due to fit? Ive trie slider (blue) but the loads are very small, I cant trust it .


thanks for any of your help












Edited by: alwaysdrunk

 

[Mloew]

MDO is a mechanism solution, not a structural solution. You need a non-linear (both geometrically and materially) Finite Element Analysis solution for this type of problem.

 

[alwaysdrunk]

I'm sorry for confusion.


yes I am aware that MDO is within mechanism. For some reason it is called mechanism dynamics is that you can use all the forces/moments etc on a mechanism connection to analyze stresses on parts and assemblies. That is called "Use in Structure" which you can export mechanism loads into mechanica structure. my objective is to get the exact load caused by the sliding mechanism on both parts including friction ang use it to analyze stress in mechanic. the problem is, I'm not getting the somehow near values of load due to friction and fit, maybe there is something I missed which I can't figure out.


thanks for the help
Edited by: alwaysdrunk

 

[brenyw]

This is a mechanica problem, requires a static contact
stress analysis. The parts are assembled to their final
location and require contact regions/interfaces defined
between all mating surfaces, plus sufficient
constraints/forces to hold the bits together.Then you
can get the hoop stresses which caused the part to split

The "Use in structure" of MDO is not for this type of
problem, it is used when the momentum/mass etc are
considered.It cannot determine the force to overcome
friction due to an interference fit.

 

[alwaysdrunk]

thanks for the suggestion I will try it

 

[KurtStark]

Predicting the friction from a tight fit is very hard, because you don't know anything about the contact forces. They are very strong dependent of the imperfection of the parts. Every Micron differnce changes the friction.


With MDO you can calculate the dynamic forces (acceleration forces) and friction ofknown contact forces (also resulting from dynamic forces).

 

[alwaysdrunk]

kurtstark


that is my first attemp to analyze this kind of problem, i'm still into consideration of this approach but also open with the above suggestion. I'll post what I'll have soon.

 

[alwaysdrunk]

I have solved my problem using contacts.thanks for your help, my prototype breaks just where proe is pointing. I gues proe is that reliable after all

thanks