Designing for Impact

[NorthernMecE]

Hi folks, I'm working on designing something that will withstand impact from a heavy piece of equipment. I have no problem figuring out how much force the barricade can withstand.

My problem is that when trying to figure out the impact force that this barricade will feel varies wildly depending on the assumed duration of impact or distance (crumple zone) of impact. This isn't a situation where we can test anything, so an assumption is sort of my best bet. I used 0.1 seconds for time duration of impact based on some stuff I found through googling, but there doesn't really seem to be a standard.

Could someone point me in the right direction? First time poster so apologies if I've made mistakes with regards to rules.

 

[dvd]

kinetic energy of impact = elastic(or plastic) energy of deformation

 

[CWB1]

Time varies with stiffness of the impacted structures. dA/dK. This is where FEA shines.

 

[GregLocock]

What frequency is the fundamental mode of the structure? The impact time is closely related to that, typically.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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

 

[LittleInch]

This often comes up for discussion.

If you go to the structural engineering general forum and click search in the Top LEFT, this limits searches to that forum and search on "vehicle barrier" Lots of possible responses.

Or try this forum and do the same.

Velocity has a huge impact on the force as it is often a squared term, but yes, there are many ways to deal with this or you can assume a certain force like the highways people do.

I'm not sure there is a "standard" for this, only lots of assumed numbers. Only you can really determine whether those assumptions are correct in your situation and what you finite limits are, what level of deformation you can accept, whether this protection or a normal occurrence etc etc.

I always think you're better off with determining how much crumple you're going to accept and then working out from the speed of the thing impacting, how much time that takes and assume a steady force to decelerate the thing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

You can look at design of bollards or vehicle barriers perhaps for some guidance.

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P.E. Metallurgy, consulting work welcomed

 

[dvd]

There is a section on designing for impact loads in this classic book -

https://www.jflf.org/ProductDetails.asp?ProductCode=DW