Impact Analysis using Abaqus CAE. Please help. 1

[Fhdak88]

Dear All,

I have just started using ABAQUS and have less knowledge about it.
However, I have been given a task to work on a problem which includes the Finite Impact Analysis of a Charpy Impact Test. Basically the Charpy Impact Test is to be modeled using Abaqus and impact analysis is to be carried out.

Set-up of the Experiment
A Charpy Impact test is a destructive test used to determine the toughness of a material. Bascially the setup is such that, there is a specimen and a striker. The striker strikes the specimen at a certain velocity and fractures it. The fracture displacement is further on used to determine the toughness. I have also attached a pic below to explain the system.

However, I have modeled the Charpy test on Abaqus (as shown in the picture attached below). I have set the Material,Steps, Interaction, Loads, Mesh etc. and tried to submit the job. The job was not successfull and displayed an error saying:
"The ratio of deformation speed to wave speed exceeds 1.0000 in at least one element. This usually indicates an error with the model definition. Additional diagnostic information may be found in the message file."

Can Someone Please guide me through my steps and help me find the problem? I will be extremely grateful.

Thank you

 

[henki]

Hi,

you are performing an explicit dynamic analysis(?). I got the same error message when I used Abaqus/Explicit. With me the problem was with the element time step. When I manually forced a too large time step, the solution failed to converge.

I would suggest you to check your time stepping option in Step-definition. If you are already using automatic time stepping, the problem is somewhere else. Maybe too coarse mesh?

-henki

 

[Fhdak88]

Dear Henki,

Thank you for replying to my post. Yes, I am performing a Explicit Dynamic test. I have also made certain changes in the design. This time i have used supports to hold the specimen (as shown in the pic attached below). I tried what you had asked me to but it didnt seem to work and i am still getting the same error. But just to be sure, what exactly do you mean by element time step?

Secondly, I would like to reinform you about the setup. The support and the striker are rigid, as there is no analysis needed to be done. The analysis that i am interested in is the specimen. Now, the striker is suppose to strike the specimen on the opposite side of the notch. In this case, intially the supports are not applying any force on the specimen.

The step setting that you have asked me to check are as follows:
Step type: Explicit/Dynamic
Incrementation Type : Automatic

Can you also please tell me about how i should set the interaction between the 1. striker and the specimen ? I have set it but i am not sure if its right or not.

P.S - I am lost. Please help

Thank you
fhdak

 

[sticksjoerd]

What can help in such cases:
Edit Step
Incrementation tab
Stable increment estimator: Element-by-element
Time scaling factor: 0.9

If you can attach a zip with your model or place it on some fileshare, I'd be happy to have closer look.

 

[Fhdak88]

Dear Stickjoerd,

Thank you for your response sir. I tried what you had asked me, it still didnt seem to work. I think the problem might be else where like in the interaction or somthing. However, I appreciate your concern and I am attaching the model below.
I will be extremely grateful to you if you can look into it.

I will be waiting for your response.

Thank you

 

[Fhdak88]

Dear Stickjoerd,

Ignore my message above as what you had asked me to change, did actually work but with a value less than 0.9. However, i have encountered another problem; The impact is taking place but the specimen seems to take no damage at all and is acting like a rigid part instead. The impact should atleast bring deformation if it cant fracture it. I am attaching the model again below, Please ignore the first set of file.

 

[reza00747]

I think you have chosen inappropriate size for your striker. small size of striker and momentum conservation law cause your striker goes back.
There is two solutions for your problem:
1-increase the size of striker by modeling extended setup.
2- increase mass of striker by mass scaling or magnifying the mass density of striker material.

 

[Fhdak88]

Perfect! It works! Thank you Reza and thank you all. I appreciate your help.

 

[loki3000]

what kind of mat. properties are you using for the test?

 

[Fhdak88]

The Specimen is made of steel :
Density : 7800
Elastic, Young's Modulus(E): 210E9
Poisson's ratio: 0.3
Plastic,
Yield Strength Plain Strain (%)

200.2E6 0.0
246E6 0.0235
294E6 0.0474
374E6 0.0935
437E6 0.1377
480E6 0.18

The Striker is made of Tungsten
Density : Modified according to the volume and mass of the striker (30.24kg in real life conditions).
Elastic, Young's Modulus (E): 410E9
Poisson's ratio : 0.28

---------------------------------------------------------

 

[Fhdak88]

I have another question.

How can i make a part (Striker) totally rigid? As in how can i increase its rigidity in order to have very negilible deformation in it since i am only interested in the Specimen.


Fahd

 

[reza00747]

you should goto contact module, define a reference point and then goto create constraint/rigid body

 

[Fhdak88]

How can I plot a graph b/w Plastic Strain vs Time?