Ballistic Impact Analysis 2

[Gumpmaster]

I have a problem where I need to predict if a chunk of steel travelling relatively fast will fracture a steel plate. The specifics are a chunk of steel munitions casing impacting an A36 plate as a result of the munition exploding. I can estimate the particle size and initial velocity fairly well. A literature review shows that the modern method of doing this is with FEA.

Is there a free program that I can use to to analyze this? Would the Impact program on sourceforge work?

Is there a method of computing this by hand? References?

Thanks.

 

[GBor]

Free? Not that I'm aware of, but there is a ballistics model implementation for Abaqus, I believe. It was developed by Materials Sciences Corporation in Fort Washington, PA (

http://www.materials-sciences.com).

If this is something that they will provide at some cost, you may be able to implement it into Calculix (

http://www.bconverged.com

or

http://www.calculix.com).

The pre-processor for calculix was not very good the last time I checked, but Roshaz (

http://www.roshaz.com)

offers a good Calculix interface for a reasonable price.

Hope this helps.

GBor

 

[KENAT]

Gumpmaster, there have been a couple of threads lately about impacts, one was a pnuematic component coming off and another was a steel cable breaking or something. I don't know if either of them would have anything, you may want to try looking.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
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[Gumpmaster]

Thanks,

I think we might outsource this problem. It's getting a little (or a lot) beyond my experience level.

I used ANSYS alot in grad school for static analysis, never dynamic, and my company now only has ANSYS CFX, I would think I'd need ANSYS LS-Dyna for this.

Any references for hand analysis of dynamic impact fracture?

 

[kellnerp]

I don't think Calculix does contact yet.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[GBor]

You may want to talk to AMPS (

http://www.ampstech.com).

Their explicit solver is very similar to LS-DYNA's (in part written by the same people), but they have only been in the US a relatively short time, so they are priced very competitively. There are some magazine articles out there discussing AMPS' ability to handle "hairy" problems similar to what you are looking to do.

I thought Calculix had some level of contact, but perhaps I am wrong. Another reason to look at AMPS with their "contact: all" capability...very impressive.

 

[EddyC]

If I was to do something like this, I would first calculate the kinetic energy of the fragments. Then I would calculate the energy capacity of the following modes of failure:

a) bending
b) gross shear
c) membrane action
d) local compression

The lowest value of all of the 4 above would be the governing mode of failure. All of the above can be done by hand, although probably with less accuracy than FEA methods.

 

[GregLocock]

Oddly enough the US Navy has published reams of data on this.

So if your fragment size is significant then there is a lot you can do using battleship technology and hand analysis.

If nothing else a google on NATHAN OKUN will give you some good background reading.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kellnerp]

I thought Calculix had some level of contact, but perhaps I am wrong. Another reason to look at AMPS with their "contact: all" capability...very impressive.

They do have aligned node contact IIRC. But that wouldn't cut it here.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[Gumpmaster]

Thanks Greg,

It looks like Nathan Okun has too much time on his hands. What a great resource. I haven't even come close to reading all of his pages, but it appears that most of his information deals with penetration of the armor plate. I don't think I actually have a penetration, more of a fracture due to impact. The Army has some good data on projectile penetration also. The one with the coolest name is the "Thor" equation.

We've ended up hiring a company that's going to do a parametric study with LS-Dyna. We'll see what we come up with. Thanks for the input.

 

[Gumpmaster]

On a related note,

I'm trying to define a failure criteria for my fracture. It's pretty difficult because of the strain rate and other effects. Our consultant said he's going to use a piecewise elasto plastic model. Ever used one of those? Any references for me to brush up on it?

I've looked into the Johnson-Cook model, but my consultant said that's outdated. The Johnson-Cook model takes into account hydrostatic stress, strain rate, and temperature. My consultant says that temperature doesn't matter too much. I have pretty low temperatures, maybe 250F. Does anyone think that would make much difference?

Basically I need something that takes into account super high strain rates, and maybe temperature. Any suggestions? Any references?

Thanks

 

[kellnerp]

Okun has a good explanation of failure modes and some software to do the calculations. His calculations are pretty simple.

He would approach your problem needing the size of the chunk, the angle it approaches the plate and the thickness of the plate.

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[ginsoakedboy]

Guys over at BakerRisk may be of some help in this regard. A discussion with them might answer some of your questions. Typically, they would do such an analysis, but you could ask them to quote for and describe their analysis method to you so you could gauge how well your hired consultant knows this stuff.