FEA simulation of syringe

[Cece Fert]

Hi y'all,

I am trying to simulate the mechanics of a medical syringe. I am trying to run a linear static analysis and I am not really concerned with running a CFD for the project. Basically I just want to simulate the plunger moving downwards when a force is applied. I am having trouble setting up the conditions in Solidworks. Does anyone have any guidance that could help?

Thank you!

 

[FEA way]

You can fix the outer part of the syringe (as if it was being held by someone) and apply pressure to the inner part. Magnitude of this pressure can be calculated from Pascal’s law

 

[Cece Fert]

When you say apply pressure to the inner part -- do you mean like in my current model?
When I run the analysis, there is no displacement of the plunger to the inside of the body (vertical direction). It kinda looks like it is fixed in place and pushing down just makes the plunger bend and deform (see picture with results):

 

[FEA way]

Do you have contact defined between these two parts ? Here you only apply load to the plunger. I would use pressure specified for surfaces inside the syringe (where the fluid is).

 

[btrueblood]

Looks like the OP has specified the plunger/body contact line to be fixed, not a sliding contact. Making it a sliding contact means you have a non-static load condition (the pressure load moves as the two parts deflect under load), a fairly tricky thing to model and likely not an option in a student-licensed, CAD-packaged, linear FEA solver. Like FEA way said in his first post, model the internal pressure with the parts fixed. You can then model the plunger forces as a separate model (pressure load on face of plunger, end of plunger fixed), similarly with the body of the syringe.

 

[Cece Fert]

Thank you for your replies -- they are really helping me understand this project further.
I will be adding the pressure internally to model the fluid on the inner walls of the syringe as well as the bottom face of the plunger in contact with the fluid.
Is there no way to apply the fixture to a sliding contact?
I am kind of confused -- are you guys suggesting that I do two separate static analyses?

 

[FEA way]

Most likely your current contact setting is bonded - parts are "welded/glued" together and can’t move relative to each other. To allow for sliding (and separation in some cases) you would have to use different type of contact - in SW Simulation it’s called no penetration. But this introduces nonlinearity to the model and may result in nonconvergence if rigid body motions are not properly stabilized.

 

[Cece Fert]

Oh, okay! I remember learning about that in my one of my other classes...
Indeed, when I choose no penetration, I get an error. Is there a way to make sure the rigid body motions are stabilized so I can apply this?

 

[IRstuff]

Is this for school? Student posting is forbidden

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Cece Fert]

It's not for a school assignment. I have already finished my finals. I am hoping to get more training before I start job interviews and I want to have functioning models.

 

[FEA way]

There are several ways to handle RBM's. SW Simulation offers soft springs and inertia relief method but it's better to eliminate them in more "natural" way - make sure that contact between parts is properly established from the begininning of the analysis and use displacement control when possible.

 

[IceBreakerSours]

Think about the solid mechanics at play. A major player that prevents the plunger from "flying away" is the interaction with the chamber, likely due to an interference fit between the rubber on the plunger and the plastic. So, you may need to resolve that interference fit first. Also, if the rate of loading can not be approximated to be steady-state, then the change in pressure inside the chamber will also come into play.

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[Cece Fert]

Thank you -- as I have only had a brief experience with FEA (with a CAD class in undergrad), does anyone have any step by step guide that could be useful? I understand what you're saying, but I am not familiar enough with the software to set up those conditions.

Thanks!!