INDENTATION WITH FORCE FOr GETTING DISPLACEMENT

[C.Amini]

Hi guys
is there any sample for indentation of rigid body on deformable plate.
i modeled it by imparting displacement to rigid body.. but when i use force on it i cant drive realistic results..
it would be nice of you if guide me this problem with imparting of force

 

[L_K]

What is specifically wrong in the results? Please share some details of the model
(boundary conditions, material model, contact definitions, ...).

 

[C.Amini]

hello L_K
we have a plate and ball. the ball should be pressed to the surface of plate.
i modeled it and imparted displacement(300micron) to pilot node of ball and observed results ( like von miss and other stresses) and checked reaction force in pilot node that was almost 24000N.. then i want to model it by force ( inverse analysis) that means at this time i imparted 24000N force and wan to see how much displacement or vonmiss stress...are.
but at this moment results dosent show any vonmiss stress or displacement( that are so low order of 1e-7)
one time i modeled ball rigid by direct generation element (Using Direct Generation to Create Rigid Target Elements) and one time i modeled contact with target rigid and pilot node by division of lines of sphere to 20.
i dont know exactly what the problem is.. because with imparting displacement i can drive result but when i impart the force equals the same displacement i dont receive any results.
I have attached log file that i imparted 30micron indentation( ball is height of 1mm from the surface) and revolve and traversed ball one round ( you can solve it by lssolve,1,2)..then i checked reaction force that was -1980N...but when i want to model it by imparting force -1980 i haven't result.
MY problem is how to do it by force instead of imparting of displacement.
thank you in advance for your time and consideration.
in reality i want to model impressed ball under force to the plate then i move it for one revolution along the plate.

 

[L_K]

I am not very familiar with MAPDL but I have encountered a following problem in Ansys Mechanical
for a similar analysis.

In that analysis the contact between parts was not established when using force instead of displacement.
I got it to work by placing the parts geometrically in contact and using "adjust to touch" option for the contact.
I also decreased the initial time step size. Is there particular reason why there is the 1mm gap between the ball and plate
and they are not in contact?

Although if that was the problem in your model I would expect it to report rigid body motion (large deformation values) because
the ball is just flying through the plate.

 

[L_K]

Also, the element size on the ball and plate should be somewhat identical.

 

[C.Amini]

hello
i modeled it in touch without any gap but the result is nothing again.truly i am executing in static analysis..would it be a cause of problem?
maybe i should model in touch without gap and increase gradually force by subsequent load steps...but anyway thank you for your response
really i do appreciate you...I am working on it..

 

[L_K]

I have seen it seen also done by using displacement load in the first load step to get the parts
barely touching. Then in second load step apply the force.

 

[L_K]

I think static analysis is correct to use.
You could try decreasing the size of first substep.
This should apply the force even more
gradually than in the current version.

NSUBST,100,1000,1

 

[C.Amini]

hello
thank you for your valuable points. i changed behavior of contact from standard to bond initial and i got reasonable results in load step 1..but now i
am doing every work for convergence in load step 2 but my solution wasent convergence.
if you encountered similar problem in ansys mechanical . it would be appreciate let me know..because for load step 1 i tried impose some changes in ansys apdl look like ansys mechanical( what you said about adjust to touch).
my plan for this solution as follows:
1- imparting vertical force on the pilot node and constraint displacements in all directions except vertical ( write load step1).
2-in load step 2 with maintaining the same force in vertical direction and impose rotation about traverse axis and displacement along the plate (write load step2)
static analysis was selected as analysis type. i dont know if i model force on rolling disc statically as i mentioned above in part2 is correct or not?


thank you again for every thing

 

[C.Amini]

hello my friend.
my model was converged by changing keyoption(4)=2 for element contact174
results almost is realistic and unrealistic but i will work on it.
i wanna appreciate you and thanks alot for valuable points that you mentioned
good luck
cyrus

 

[C.Amini]

but i have question and i think maybe would be simple that i dont know its answer.
if in the same model i want to model cylinder or other object to move along the path( the same path that ball has gone) what do i do? i mean how deactivate ball in my model,,because i need plate ( with initial condition due to ball) and new modeled object. can i delete ball then model new object?
i know it relates to restart but i want to deactivate ball in subsequent simulation.
thank you

 

[L_K]

For deactivating ball/activating another object during analysis you could look into ekill/ealive commands.

 

[C.Amini]

thank you L_K for the response
as i mentioned above i modeled movement ball on the plate by direct generation tar get element. but results are somehow unrealistic.
i want to model in other method and my problem as follows:
the simulation is 2 step: ball impressed to the plate, second step: impressed ball moves along the plate and simultaneously it rolls. but in the end of second step ball full penetrate on the plate(so that some part of ball passes the bottom of plate).
what can i do for it?
description of contact: contact lgoritm:AUGMENTED Lagrange ,detection point:normal to target, behaviuor:bonded(initial),...
that is so important for me.. thank you again

 

[L_K]

You could try using more elements on the ball (

https://www.dropbox.com/s/c5d6dlakyw61buz/coarse_mesh.JPG?dl=0).

The model will achieve convergence better if the mesh is about the same size on both target and contact surfaces.

 

[C.Amini]

HELLO
the photos that sent to me it belongs to direct mesh generation of target that i modeled it but results are not good. the model that now i am working on it include of ball with finer mesh (indirect mesh generation). i attached photo of it..but it wasent converged. even i refine mesh of sphere but...
thank you so much