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IMPACT/CONTACT Analysis

IMPACT/CONTACT Analysis

IMPACT/CONTACT Analysis

(OP)
Dear All

After Rob's suggestion I am making this a new thread and including the original question and answers from the previous thread.

Before I start my question, I would like to appreciate the efforts of people helping each other, thats reallt great.

My question is that I am trying to model a 2D contact problem (indentation of a steel sphere on rectangular Alimunium plate). Now as I am a beginner. I have modeled the plate with Aluminium properties and steel with its properties. Made contact with each other and defined steps and applying displacement load on top of the indentor. The application runs successfully. But what I am trying to achieve is that it shows the deformation when applying load on it. But i also want to see when we remove the indentor how much deformation remains after unloading. So the problem is unloading and do i have to create a seperate step for that, and if i do, both part will still be in contact so how do i do that.

please do help me in this regard as I am really struggling.


Thanking you in advance



  
 

rstupplebeen (Mechanical) 28 Jan 10 9:19  
For future reference this should be in a new thread.

You can do this a couple of different ways.  Create a new step and have the displacement go back to zero.  Or, Create an amplitude that the displacement references that ramps from 0-1-0 for time points 0-.5-1.

You will need to include plastic deformation for the aluminum plate otherwise you should have no residual stresses.

I hope this helps.
  
Rob Stupplebeen
 
 

iyj (Mechanical) 31 Jan 10 2:20  
Dear Rob

I thank you alot for these helping comments and suggestions. I will try these out and will let you know the outcome too. Once again thanks alot and really appreciate your effort.

Best Regards  
 

iyj (Mechanical) 31 Jan 10 7:04  
Dear Rob

It really worked I am so happy, thanks alot really thanks. While attempting the case there was a minor issue and that was when it was unloading it was not going to its original place. like fist displacent i gave was (U2= -0.05, ), and the second BC was U2 = 0, rest remain unchanged. i wanted to to see the final force comning back to zero. The plastic thing really worked, thanks.

Please do let me know where i am wrong.

Regards  
 

iyj (Mechanical) 1 Feb 10 6:11  
Dear Rob

In the second step which is the unloading, instead of force going back to zero it actually increases. I already gave the displacement(U2=0) for the final step, but still this problem occurs. Do I have to disconnect both the parts so there is no contact in between them. if yes How do I do that?. Can you please let me know.

Or if not plz can you correct me where I am wrong

Thanking you in advance


Regards
 
 
 

RE: IMPACT/CONTACT Analysis

What force are you calculating?  Could you post your model or provide some pictures.  At the end of the second step is the indentor sill in contact with the plate?

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I thank you for replying. Ok I have attached the CAE file for the model please do have a look. Also I will de sending you a graph in the second post of which type of graph I want to acheive.

After your suggestions I am able to remove the contact by removing the load in the second step. Also I am calculating the applied force to this plate in terms of giving displacement value. Is this correct. Please do let me know.

In this problem I am using the indentor as a rigid body.I wanted to ask that if i can give steel properties to this same indentor and remove rigid body, will that work. because that is what i want to acheive at the end. Steel indentor and Aluminium plate.

I thank you in advance and await your response


Best reagrds
  

RE: IMPACT/CONTACT Analysis

For your reference point you are translating it in the U2 direction for step 1 and then holding it there for step 2.  Additionally in step 2 you translate the same point to 0 for U2.  Instead just modify the displacement of the first constraint in step 2.  

The force displacement methodology looks good.  The indentor can be deformable.

I hope this helps.
 

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

I just ran your model with the suggested change above.  There is very large deformation of the mesh which is causing poor aspect ratios.  I would reconsider the fixed constraint on the bottom face.  My guess is that it can translate in the 1 direction.  If these loads are accurate then you will need to use adaptive remeshing  to get a valid solution.  I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I thank  you alot for the effort you're making for me. I have tried doing what you have suggested, but when i try to use adaptive remieshing rule, it does not let me do it and gives a message of (that orphan meshes cannot be changed) and it does not let me delete the mesh for some reason i dont know.

Also can you tell me which type of part i can use to model the indentor with. like if i use deforemable type part than how should i model it. i want to model this indentor with steel properties, so will i use the shell-homogenous properties. Please help

Best regards

 

RE: IMPACT/CONTACT Analysis

You have an orphan mesh.  Create the rectangle in CAE.

Deformable shell with steel properties.

I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Thanks alot, Yes I have created a new rectangle and modeled the indentor with the deformable shell with steel properties. All goes well, thanks to you. There is a single question that i need to ask you that is where will i apply the load on this indentor and how will i remove it.
As previously it was a reference point in the rigid body now in this case i applied in the middle of the indentor, but when i use the same location for the unloading and error comes. I have chosen end points of the indentor which does not make sense.

I have attached the new CAE file for you to look and if possible can you please identify where shall i apply and remove load on this indentor.

Really thanks man

Best regards

 

RE: IMPACT/CONTACT Analysis

In the boundary condition "Applyload" for the second step return the indentor to 0 or even a little above the original position.  "removeload" is not needed.  The constraint at the bottom of the plate I still believe should just constrain in the U2 direction.  I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

I would also apply the displacement to the entire top face of the indentor.  Applying to a point usually if not always creates locally large deformations.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I couldnt thank you more. I have made changes according to your input. I have applied load to the top face of the indentor and also removed the second (remove load from the boundary condition). The analysis runs fine, but when i animate the indentor actully goes inside the plate and the deformations are not that are required really. I have attached the new CAE file for you to look at.
Please just run it and see the deformations. Also i have only constraint in U2 direction as you suggested.

Thanking you in advance

Best regards

RE: IMPACT/CONTACT Analysis

I have looked at the model and here are my thoughts.
1. BOT should only be in the U2 not U2 and U3.
2. Try using second order elements for the plate.
3. Do you have an appropriate displacement?  The deformation seems small but I am unfamiliar with the actual test.

I hope this helps.
 

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Thanks alot for these gelpful tips. I have tried using your suggestions, but you know it is still overlapping and going inside the plate. I know you are right its to do with the type of element i have to choose. For the element bit as you suggested to use second order elements for plate. What i did i selected the element type and ticked the option of second order, is that the correct way of doing it or something else. please do advise.

I also have a question relating to impact of the indentor to the plate, in the same model that is attached with this post. Can you please tell me if i want to give velocity to the indentor and want to see how it impacts with the plate and rebounds, do i have to use Abaqus Explicit analysis for that. and where do i give the velocity, as i have to give around 2.5 m/s to the indentor.

Really grateful to you


Best regards

 

RE: IMPACT/CONTACT Analysis

Is there a way to apply a density and a stiffness to the rigid part?

Many thanks for your help

Fabian

RE: IMPACT/CONTACT Analysis

CAE calls second order elements quadratic and can be accessed in the element type dialog.

For impact you will need to use explicit and provide the indentor with an initial velocity.  This will be a much harder problem to solve and should probably be a new thread.


Fabian,
Sorry I do not have time to look at the models.  This should be a new thread instead of adding on to iyj's.  A rigid part has infinite stiffness.

I hope this helps.
 

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Thanks alot. I will do as you suggested. I will start a new thread for the impact analysis and will let you know.

Best regards
 

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Just a quick question, I wanted to know if the units i am using are right, Please check my model and do let me know if I have inputted them rightly.

I am using the dimensions in meters

indentor Radius = 0.0828m
length of plate = 0.090m
Youngs Modulus E = 7.9 Gpa
Density = 1580 kg/m3 ( I have input it just like this)is this correct).
Yield Stress = 202 MPa
load applied in Boundary Condition is = 0.001093 m

so the resulting force and displacement is in Newtons and meters? Please do let me know.

Also can we give steel properties to the rigid indentor?

Thanks alot


Best regards



the resulting graph co

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Thanks alot, this was really helpful and made life alot easier. Thanks once again.

I have been tring the same problem again with complete sphere in 2D making contact with the rectangular plate. I have designed the sphere(indentor) rigid with steel properties, as u can see in the attached file. once i apply displacement it goes into the plate without making a deformation or permanent deformation. I even gave plastic properties to the plate material too. It worked with the rigid wire, but this is the actual problem, an di have seen in some of the papers they have done similar model.

I know you have suggested earlier that i need to use the second order element, itried but still it did not work, i dont know why,is it the interaction between both surfaces?

Please do check the model please do let me know where the problem lies as i have tried ven refining the mesh but it still goes inside the plate and not showing the deformation. if this is acheived than we can unload it too. Right now I am only trying loading case.

Thanks alot Rob

Best regards


 

RE: IMPACT/CONTACT Analysis

Once you make the indentor rigid it is not steel anymore it is infinitely stiff allowing only RBM (rigid body motions).

I believe your lack of deformation is that your mesh is very large compared to your displacement.  Your mesh is 2.5 and your displacement is 0.02.  

Make sure that on your deformation plot that you do not have a scaling factor applied.  That can be real confusing if you don't notice. Options>Common>Basic>Uniform 1

I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

You are currently modeling this as Plane Strain.  So basically you are modeling a bar indentor instead of a sphere.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I thank you for yuor helpful advice. I am sorry i could not reply earlier it was due to holidays in this part of the word for national day.

I have tried using plane stress elements and also refine the mesh density and i can see some deformation but not complete only in the middle node and the the one below, you can see it too, i have attached the CAE file with this post. All i did was used plane stress and quadratic elemts in the plate and used linear for rigid indentor.

What seems to be the problem, do i have to make the mesh more coarse or is there a problem with the element defination.

I have modeled the sphere with deformabls shell and than make it rigid, is this the problem. please advice.


Best regards

 

RE: IMPACT/CONTACT Analysis

Plane stress elements are for sheet metal like parts such as a car hood or airplane wing.  You need to use axisymmetric models for geometries that could be turned on a lathe.  So if you want a 2D model of a spherical indentor then you need to model this as axisymmetric.  

Only draw the +X half of your model and convert to axisymmetric for the part instances and the element types.  

I hope this helps.
 

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I thank you for the suggestions. I have tried the way you have suggested and have designed the model as axisymmetric and used axisymmetric elements too. The analyis runs fine and is successful but i get this message when it comes to see the results.

"Results for current deformed variable are not available for one or more nodes constrained in the model.Deformation of such nodes are assumed to be zero"

I dont know why this message appears. Any suggestions on that. I have attached the new model please do have a look if I am somewhere wrong than please do guide me.


Thanking you in advance

Best regards

RE: IMPACT/CONTACT Analysis

Reduce your initial step size.  Basically for a nonlinear analysis a single step is never appropriate.  

Mesh:
Try changing your plate's mesh to sweep instead of structured.

Boundary conditions:
The fixed constraints are still probably not appropriate.  Review my previous posts.

I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I have tried the model with your suggestions. But it is still giving me the same error.

"Results for current deformed variable are not available for one or more nodes constrained in the model.Deformation of such nodes are assumed to be zero"

Is it to do with the constraint that i have used i wonder. As I have modeled the sphere with rigid body. I am confused and cannot seem to find the problem. I have attached the model with the changes you suggested. I am really grateful to your effort in this regard.


Best regards



 

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I hope you are fine and in best of health. Actually i wanted to update on my progress. I have got rid of the error that was appearing agaian and again, the one mention in the last posts. Thanks to you really.

Now that i can see the results, i cannot see deformation, instead the sphere is sliding on the plate and not bending or deforming the plate. Please do let me know why is that happening now. I have fixed the left edges of both sphere and plate and still the sphere moves in the opposite direction, i dont seem to figure out how and why. please see the attached CAE file.

Please do guide me on this

Thanks alot really

Best regards

RE: IMPACT/CONTACT Analysis

I am not sure where you model is going wrong without really digging into the details so I made a test case.  I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Thanking you will be a under statement. I think you just have saved my job and i am really grateful to you, for the effort you have made for me. It really works they case you did and that was exactly what i was looking for.

Now I can move to Impact of these two parts and as you suggested i have to use dynamic explicit steps for that and have to give velocity to the ball.

Once again Rob you are a saviour and a good teacher to me. Now I will start the impact problem and as you suggested will make another thread for it too.

I will let you know about the new thread once i have started the problem.

Best reagrds



 

RE: IMPACT/CONTACT Analysis

I'm glad I could help and you are very welcome.  Thank you for your kind words.  Good luck with the explicit analysis.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

I hope you are fine. I just wanted to know that the dimensions you used for this example, are they in meters or millimeters. I checked the radius of the indentor its 0.5 so is it in meters or millimeters?

As the corresponding force -time graph and displacement graph that i draw i am gettin a bit confused, I remember you sending me the reference list to follow, but if you could tell me the initial units it will be easier to follow.

Thanking you in advance


Best regards

RE: IMPACT/CONTACT Analysis

I just put in arbitrary values for geometry, materials, and displacements.  You should be able to go back into the model and change them to your values with little effort.  Modify the: sketches, material property, displacement and remesh.  I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear ROB

I hope you will be fine and in best of health. Long time no contact as i was abroad and now back to work.

After your helpful guidance i was able to make the model to work according to my specification. Now if i want to run the same thing like still a static case but in 3D, will the procedure be same. And all i have to do is to model both objects with 3D elements and use the same technique as the one you used. please do let me know.

Thanking you in advance

Best regards



 

RE: IMPACT/CONTACT Analysis

I believe so.  It will take a lot longer to solve though.  Pay attention to constraining the additional degrees of freedom.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

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 help

Best regards

 

RE: IMPACT/CONTACT Analysis

(OP)
Dear Rob

Just a quick question, I am using this same contact analysis using elastic plastic material of the plate. the forces seems to be too hight as compared to the analytical solution and thats not right. I may be giving the wrong plasticity module from the material list. The Yiled stress is 202E6 MPa and i normally give the plastic strain a value of zero. please guide me on this. As the elastic case compared well and but this ealstic-plastic case there must be something wrong that i am inputting. please have a look at the attached cae file.


thanking you in advance

Best regards

 

RE: IMPACT/CONTACT Analysis

I usually leave the plastic strain blank if I am just using yield stress.

I believe that you may have a units issue.  Is your model in mm?  If so pressures should be in MPa (modulus, yield stress).  I hope this helps.

Rob Stupplebeen

RE: IMPACT/CONTACT Analysis

Quick question. Is there anyway of obtained 'contact stress' as an output from Abaqus 6.9? Thank-you.

RE: IMPACT/CONTACT Analysis

CPRESS (contact pressure)

Rob Stupplebeen

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