50 G's transportation loading??? 2

[scottr99]

Hello, I am analyzing the integrity of a plastic casing holding two 7lb batteries. The loading is 50-g's while it's standing on end, which is supposedly what it could see during transportation by truck, cross-country.

What I am having a hard time with is the 50-g's and how to account for the shocks and springs of the vehicle. If I use a hard surface below the plastic pack, there's no way it could survive 50-g's, nor could anything I would imagine.

Has anyone done an analysis dealing with transportation g-loads of this magnitude? Any help would be greatly appreciated!

Thanks,
Scott

 

[zekeman]

You can be sure that the 50 g's is not ON the truck. Imagine the truck driver having to survive that.
Find out the origin of 50 g's. A more realistic and usual shock spec would be a sudden drop at some height.Then the container can be made sufficiently absorbent to safeguard the contents.
Vehicle transportation is usually more modest since there is enough shock absorbing capability that the driver will survive.

 

[tygerdawg]

It may be important to determine the duration of the 50g acceleration. It could be an impulse loading spec.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[KENAT]

Is the 50g already an approximation of the shock/impulse loading? Like zekeman & tyger say, I'd try and find out more information about the loading case and any assumptions etc already included.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

 

[scottr99]

Thank you for the responses. It appears that it is indeed an impulse loading requirement. The duration is what I'm going to have to maximize to withstand this loading, presumably by using some kind of spring under the boxes of casings.

 

[IRstuff]

50 g sounds more like a crash shock from which no survival of equipment is required, only that it stays put and break loose and smash someone.

TTFN

FAQ731-376

 

[IRstuff]

stays put and NOT break loose and smash someone

TTFN

FAQ731-376

 

[Twoballcane]

In my past experience 3 to 5 Gs for transportation. Also, tygerdog is corrected, you have to know the duration so that you don't design somthing that cause shock amplification.

Tobalcane
"If you avoid failure, you also avoid success."

 

[MintJulep]

What is the direction of the 50 G shock?

I see that as an entirely reasonable design assumption for something that actually needs to survive a truck ride.

 

[GregLocock]

50g is around the acceleration seen during a 30 mph crash into a large concrete block. As such, if you don't want the batteries to come loose in a crash, that's the load you need to pass the test. The duration of the pulse is easily derived from the crush distance of the vehicle, somewhere between 0.3 and 0.7 m.

Compliance (springiness) will be your friend.





Cheers

Greg Locock

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

 

[scottr99]

Thanks again for all of the help. We are looking at using layers of corrugated cardboard to be used under the casings for a spring effect, essentially increasing dt in the impact force equation F= m x dv/dt.

Thanks again all.

 

[FeX32]

I don't think F=ma is sufficient for this one. Look into an energy/ momentum method.
However, you have the part about increasing the dt correct.
just a thought,



Fe

 

[racookpe1978]

Might be 5.0 g ?? Somebody slipped a decimal place in the re-write of the spec of contract.

(12 - 15 G is the maximum the older astronauts went through on the end of their rockets. It's NOT normal truck transportation of ANY survivable accident or collision of the tractor-traqiler on rubber wheels.

However ..... It might be the drop-from-six-foot that a (stupid) employee does by letting go of the battery above a concrete floor.

The requirement then is that the outer case (doesn't leak!) survives a drop so no acid is splattered all over the floor and adjacent customers.

If so, ridges or compressable edges on thepalstic case would deform and prevent the case from splitting its corners apart. The battery internal might be destroyed, but the acid is contained.

--

Bottom line? find out WHY the requirement is written and WHAT the "condition" of the battery needs to be after the drop/collision/rocket launch.

 

[KENAT]

racookpe1978, can't remember the figures but I believe an adequately restrained person in a collision or similar can see a lot more than 15g and survive it with out too much damage.

I vaguly recall some guy strapped into a rocket sled hitting ridiculous G forces. He blacked out but suffered no permanent injuries.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

 

[Adalius]

Kenat,
The man you speak of is John Stapp, he reached just a little over 40g's in the rocket chair. More info on it can be found at Fastest Man On Earth

 

[KENAT]

Guess my memory was playing up a bit, some of those injuries sound at least semi permanent!

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

 

[waross]

You may want to check if the 50 G requirement is vertical as the result of hitting a pothole or dropping a skid, or horizontal as the result of a collision. Might make a difference!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[GregLocock]

There's a milspec for road transport vibration levels, that may give you some context.

Cheers

Greg Locock

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

 

[IRstuff]

That would be MIL-STD-810F Method 516.5
see procedures:
IV --> Transit Drop - more like an 800-lb gorilla's oopsies
V --> Crash Hazard - 75g 6 ms
VII --> Rail Impact - rail car impacts at 6.4, 9.7, 13 km/hr speeds.



TTFN

FAQ731-376

 

[HDS]

There are also specs from ISTA, ANSI, and FedEx that all describe tests for truck transportation.