Simple Question on Prescribed displacment

[james.lynch]

Hi All,


I'm having a bit of trouble- I'm sure it's something stupid that I'm doing wrong and I'm hoping that someone here can help me!


Anyway.. I would like to use mechanica to analyse a type of live hinge but I'm having dificulties setting up the model corectly.


I have shown a simplified example of my part below - it is moulded at an initially bent angle of say 30 degrees.


View attachment 4394


I would like to essentially rotate the top section so it lays flat


View attachment 4395


Then rotate the top section so it it is at say 60 degrees


View attachment 4396


The real model has to be a solid 3D model - I'm working in WF 3.0 integrated mode.


What I've done so far is to constrain the lower section fully, then I took the top edge of the top section (highest point of the above picture) and constrained it with an initial displament of 2mm and left it free in all other directions/rotations - I had to apply a dummy load of 0 to get the model to give any sort of result..


What I am trying to do is instead of trasnslating the edge, I would like to rotate the top surf (highlighted below) from the initial 30 degrees to 0 degrees and then to 60 degres (specified in radians) -


View attachment 4397


My ultamate goal is to obtain reaction forces at all angles between 0 and 60, optomise the design using BMX or Global optomisation studies and run a fatigue study to estimate life.


Any and All help is greatly appriciated!


TIA.


James
Edited by: james.lynch

 

[ankarl]

Think you have to use a shell or beammodel for this


"Note: The software ignores any rotational degrees of freedom for 2D solids or solids in 3D models. If you specify constraints on Rot X, Rot Y, or Rot Z for these elements, the software ignores the constraints."


Hopefully I'm wrong, like to know how to use this in 3D-solids as well.

 

[james.lynch]

Hi Ankarl,


Thanks for the reply, I have a "bad" 3d model working, I'm not sure why I'd have to use a simplified beam model (but then again I've been out of the FEA scene for a while) - can you expand on the reason for this?


my 3d model is set up like this


View attachment 4406


and it moves like is shown below..


View attachment 4407


however, this is incorect -


Still struggling here

- Any more help out there?


Thanks!


James

 

[ankarl]

solids has only3 degees of freedom( translation only), shells and beams have 6 (trans and rotations). Why? No idea, dont know the math behind it ....

Have you tried with a cylindrical csys as reference for the translation? (wild shot)

 

[james.lynch]

Hmmmm.. strange.. but I'm sure there'e a reason for it..


would it be possible to create a layer of shell elements on the surface which I want to rotate? I'm not sure how to do it but maybe it'll work..


If anybody has some experience with this I'd greatly appriciate some help..


I'll post any progress I make later..


TIA,


James

 

[james.lynch]

ok..


So I've created a set of shell elements offset from the surface that I want to rotate, I then created a set of rigid links between theoffset and original surface. I meshed it, applied a rotational displacment and it seems to be working!


View attachment 4410


BUT...


on examining the results it looks like the deformed area is not performign as expected.. or maybe it is and I'm missing something..


View attachment 4411


The area where the red arrow is pointing is expanding (area of rectange at an angle is greated than the undeformed area).. There is a scale on theabove result setso exagerate it.


Would this be correct? hmmm.. Anybody shed some light?


James

 

[james.lynch]

by any chance is there a suggested technique for this? (I did tack a good look but maybe I missed it?) It should be a fairly common thing..


James

 

[JaimeMorenoT]

James,


I usually don't post here but I this time I would like to contribuite to the Pro/E community. I try to help people that try first and then ask.


You need to fix the bottom surface and apply a pressure to the top surface. The pressure will follow the surface once it starts to move. You will have to usethe large deformation option with increments on load (pressure). Use ten increments and space the load equally. See picture below for the results I got. I also attached a pro/e file for your reference. Depends on the material you will need a corresponding pressure to flex the hing to the desire position


2007-11-12_224157_Hinge.zip
Edited by: JaimeMorenoT

 

[james.lynch]

Jamie - Thank you kindly for your tip! The results (well how the model deforms) look fantastic!
I haven't got Mechanica on this machine so I'l have to wait until this evening to try it - but I really would never have thought to use a pressure load to deform it..

Anyway, thanks to all who have helped in solving this problem - it was really appriciated! I'll post how I get on later tonight.

Kind regards,

James