Impact Dynamics

iyj · Apr 12, 2010

Dear All

I hope you are fine and in best of health. I have started working on impact analysis and staright away some questions. I am using the same geometry that i used for contact analysis, the axisymmetric model using axisymetric elements.

Now what I am doing is that I have changed the analysis to dynamic explicit and instead of displacement i have given a initial velocity with the poin mass to the analytical rigid part. It works fine but But i want to see the impactor to impact the thick plate and than bounce normally as it happens in the real time.Do I assign gravity to the impactor or whats the slotion.

I want to see the force Vs indentation of this impact. I know you said I have to use different thread. I will make a new thread and post this on that too. Please helpBest regards

rstupplebeen · Apr 12, 2010

I would give the rigid part an initial velocity based on the drop height. Have the part very close to the plate for the start of the analysis and include gravity. You can obtain the force from the constraints on the plate and the indention by the location of the rigid part's reference point. I hope this helps.

Rob Stupplebeen

Nileo2005 · Apr 12, 2010

I'd have to agree with Rob's suggestions; they are good ones. Do the simple physics calcs to find out how fast your part should be moving at the point of impact and instill it with this speed at its RP, placed very close to impacting. You need to do this or Explicit will waste a lot of resources calculating something as simple as the part accelerating in gravity. Calling for RT or RF on the RP of the plate will allow you to measure the reaction force of the impact.

iyj · Apr 13, 2010

Dear Rob and Nileo

Thanks for your valuable suggestions, I really appreciate it. I have run the case with your suggestions, but there is a problem. When I assign the gravity load to the analytical rigid reference point, it does not recognise it and gives an error unknown assembly to reference punch.

I have attached the CAE file for you to look at and you can run the job named impac2 to see the results.

Please tell me how do i eradicate this problem and where exactly i give the gravity on the analytical rigid part.

Best regards

rstupplebeen · Apr 13, 2010

1. To get the initial velocity I create a separate short step to give the velocity then in the next step suppress it.
2. Nlgeom: On
3. Apply an inertia to your reference point. I think this is what you did though. I would try redefining the inertia possibly not in a set.

I hope this helps.

Rob Stupplebeen

iyj · Apr 14, 2010

Dear Rob

Thanks alot for the useful tips. I have tried they way you suggested but i dont seem to get the gravity where i want. As you say I need to apply gravity, so i try to apply in on the reference point of the analytical rigid part but it does not work, it gives me an error

[DLOAD, file "impac2.inp", line 10284: Unknown assembly element set REFPUNCH
Error in job impac2: ELEMENT SET ASSEMBLY_REFPUNCH HAS NOT BEEN DEFINED]

What shall i do, where shall i apply the gravity load.

Also the mass of the impactor is 0.5 kg and I have applied to the reference point of impactor.

Best regards

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