Gravity with rigid body

[irene01]

Hello all,

My model consists of three parts: impactor, plate and supports. On the supports the plate is located and the impactor is dropped at great speed. The object of the study is to determine the stress, energy released in the impact... with this objective, I have thought that it could define the impactor and the supports like rigid solids using (Discrete Rigid or Analytical Rigid) but when attempt to define the gravity acting on the complete model, if attempt to apply the gravity on the node of reference of the impactor, Abaqus not permite it.
(Module --> Load -->-Create --> Gravity-->....)
How I can define the gravity acting on the set? . When I define the gravity in a deformable solid is no problem. Why yes in the case of rigid solids? There is something is not doing well?

Please, help me.

 

[gelu]

I think the solution can be to add a mass element to the reference point of the rigid solid and to apply the gravitational field to this mass.
Regards

 

[gelu]

I ask about mass scaling because wasn’t very clear for me what happened with the model.
So the model seems to keep the same deformation doesn’t matter witch mass you give to the impactor (please confirm if I well understand).
You must give more details: kind of analysis (standard or explicit), BC (speed field or displacement amplitude).
Regards

 

[irene01]

Hello gelu,

I am working with Abaqus/explicit.
I define the speed of the impactor in the reference node and restrict in this node all the displacements (except the vertical) and rotary.
My problem is that I do not know what option I must use when I am in Step --> Manager --> Edit --> Mass scaling.. in mass sacling appears two options:
1)scaled mass and "throughout step" definitions from the previous step.
2)Use scaling definition below...(and options appears such as semi-automatic, automatic..)

what I must use? What I want is to see as it affects the change of mass in the impactor to the deformation and stress of the plate on which impactor saying hits.

please, help me gelu,

thanks in advance

 

[gelu]

My best guess is your problem is mass scaling related. What I think is happening your model is scaled in mass term but only for the deformable side and the difference between the mass of the point mass and the plate mass is so big and you see the same deformation all the time. The proposed solution is:
Step/mass scaling/use scaling definitions below/semi-automatic mass scaling/whole model (or better put only the plate like this is no doubt)/at the beginning of step/scale to target time (put a value like 5.E-6 and adjust after depending on calculation time)/live all other option to default values.
Run the job interactively, look to mass scale factor and adjust in next run the mass of the impactor with the same factor (normally you will need to increase the mass).
To have an accurate solution I think will be necessary to change the way you apply the kinematics (change for an amplitude displacement for the same amount of kinetic energy and like this the mass point become unnecessary) or change the rigid impactor for a deformable body and include them in mass scaling process.
Success

 

[irene01]

Gelu, thanks very much,
I am going to prove what you say to me and to you I will maintain informed into the advances
Bye!!

 

[charlesbreen]

I have been making Explicit impact models with a rigid impactor and deformable plate for a while. I found the best way to apply "gravity" to the impactor was to just apply a concentrated force to the ref. point equal to that which it would experience due to gravity. Of course if your impactor is not uniform and symmetric about the vertical axis then this won't be applicable in your case.

Charley

 

[irene01]

Hello Charley,

if I apply the gravity like a concentrated force, Can at the same time define the initial speed of the impactor and this force?

Regards, Irene

 

[charlesbreen]

Yes you should be able to.

 

[irene01]

Hello Charlesbreen,

> When I define the gravity like a force concentrated in the reference node, it continues happening the same, independently if I apply a force of 58Newton or if it is of 200Newton etc.. the plate becomes deformed the same amount thing that I know that it is not possible then to greater load, greater must be the deformation What is happening?
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