LS Dyna Impact Analysis....object not rebounding after impact

[jhp1981]

I am new to LS Dyna. I setup an analysis in FEMAP and ran it using Dyna solver. The results look OK except for the fact that my object doesn't rebound after impact. It keep going. I ran it to 1 sec. What am I doing wrong? Material?

 

[swimfar]

It looks like the simulation is working correctly. My guess is that you have one of two issues:
1. Your assumption of what "should" happen is incorrect.
2. There's something wrong with your geometry, material properties, impactor velocity/mass, etc.

This impact looks like there's going to be a lot more plastic strain than elastic strain. So I wouldn't expect much rebound. But that's assuming that the impactor did eventually come to a stop. Based on your displacement-time plot it looks like you have way too high of an impact energy, or your tank is way too compliant. Also, you would save everyone a lot of time trying to guess what you want to do if you would show us the analysis you are trying to recreate.

 

[jhp1981]

@swimfan

At 0.5 sec the velocity went from 211.2 in/sec to 211.02 in/sec. The ram has to slow down a bit more than that in 0.5 sec. My guess is that my material is wrong but I am not sure what.

I just have the report from that analysis. What info do you want? I have deformation plots, material curves etc.

 

[IceBreakerSours]

Here is what I see:

Are you using a single precision or an SMP binary? I am using MPP R12 double precision binary on Windows 10.

Your results make me think the ram is not even seeing the cylinder i.e., contact is not working.

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[jhp1981]

@IceBreakerSours

LS Dyna 4.7 Student Version
Windows 10 64 bit

 

[IceBreakerSours]

I think 4.7 is the version of the graphical user interface (LS-PrePost). It's the binary I was asking about. Open the D3HSP file and paste the name of the binary. For instance, mine says: Revision: mpp d R12-1032-gb1be2fbad8

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[jhp1981]

@IceBreakerSours

Revision: smp d R12-1081-gb2b2774cf7

Just saw your post@ 05:30. So your plot says the ram rebounds 12" after around 0.0125 sec?! The contact does work with high ram density. But at steel density it goes through the tank. ie. contact is ignored.

Thanks for taking the time to help me.

 

[IceBreakerSours]

Try using the MPP binary; some contact cards don't work the same way between SMP and MPP binaries.

*MAT_ELASTIC_TITLE
Rigid Steel
$#     mid        ro         e        pr        da        db  not used        
         3[b]7.33000E-4[/b]2.90000E10      0.32       0.0       0.0       0.0

I am using the density you had specified in the first job you uploaded.

I am not sure if I agree with your interpretation of what my plot is showing. The rebound starts at around 0.0125 sec and continues for the rest of the analysis (i.e., t=0.3 sec).

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[jhp1981]

@IceBreakerSours

Looks like my student version doesn't have a MPP option. Just SMP Double.

 

[IceBreakerSours]

You have ANSYS to thank for that

Try a few different contact cards to see if one of those does the trick for you.

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[IceBreakerSours]

Use mortar contact i.e., try adding MORTAR option to CONTACT_AUTOMATIC_SURFACE_TO_SURFACE. You will take a small penalty in terms of computational expense but it is worth a shot if you are looking into options.

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[jhp1981]

@IceBreakerSours

I think I am close. I thought I got it to work but then I tweaked something and now the ram doesn't rebound unless I reduce its density. Do you know how to use the airbag simple pressure option? The tank is filed with liquid so after impact the internal pressure in the tank will push against the ram. What about mat damage gissmo? I want to delete elements that are above 1 triaxiality. I have a curve for all 3 materials. Thanks.

 

[jhp1981]

I finally got it. I had to fix the contacts and tweak the airbag setup. Thanks everyone!!

It is not perfect but close. My only issue is that for some reason my internal energy increases a bit after impact and then remains there. I would expect it to go down after impact.

Anyone here familiar with mat_damage_gissmo? I have these triaxiality models that I would like to use to delete elements above damage factor of 1.

 

[IceBreakerSours]

Material parameters are used to compute contact penalty stiffness factor. I suspect if you play with the contact penalty stiffness, you will see appropriate behavior. In relation to GISSMO, DYNAmore put a few good videos up on YouTube; start there.

*********************************************************
Are you new to this forum? If so, please read these FAQs:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083