Drop Test 3

[ali4design]

Drop Test of a rectangular Box

I want to do a drop test analysis of a Steel box with inside full of concrete. And planning to drop from a height of 1 meter. Falling towards the covering plate cornor. The dimensions are mention below.
I would like to know Is there any Hand calculation to find the stress produced in the box.

Dimension of Outter box : 400 x 400 x 400 x 10 mm
Inner box : 380 x 380 mm
Box covering Plate : 400 x 400 x 400 x 10 mm
Surface : 800 mm x 800 mm

Can any one sort this issue calculating stress by hand calculation. For drop test.

 

[Twoballcane]

Hmmm...is this for school?

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[rb1957]

if the box is full of concrete, what's the "outer" box ?

if it's hitting the "surface", how thick and how supported ? these affect the resiliance of the surface, and so the duration of the impact, etc, etc ...

then, of course, where on the surface ? and what orientation of the "box" ? point (corner) first ?

 

[ali4design]

Hi rb1957

The outter box is made of steel.
Inside that steel box concrete is added.
As I mentioned it ll b 10 mm thick walled box.
Duration can be found out by knowing the height of drop and "g".
The tip ll b hitting the ground first as the centroid and the tip will be constrained to have 90 deg. with the ground.

Thanks

 

[IRstuff]

"Duration can be found out by knowing the height of drop and "g"."

That's not what he was asking. That's the duration of the drop, not the impact. You need to have some idea of how long it takes from the instant the corner of the box touches the table to when it stops touching the table.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[racookpe1978]

Where is it landing?

Corner? Flat bottom? Edge? Unknown?

What is your limit on the (de)acceleration of the contents of the box: OBVIOUSLY - I don't care if a box containing concrete falls on the floor - unless somebody is underneath it, or unless the floor is going is going to break.

 

[ali4design]

It lands on the floor only... on concrete slab.
I just want to check whether my stress results of Abaqus are correct or not.I am getting around 350 Mpa. the total weight of box including inside box is 236 kg.

Can anyone tell whether this figures are correct or not.

As this cross check is for just to validate my results.

Thank you

Ali

 

[FeX32]

You never answered Tobalcane's question......


Fe

 

[rb1957]

how long did you allow the box to decelerate ? the box has momentum at the beginning of the collosion is converted into a contat force as a function of time. you have the advantage of having a rigid and massive surface to collide with. also, having the steel box supported by concrete means it won't be deflecting much, and you've oriented the box so that the contact force is through the center of mass of the box ... looks like you're left with squeezing the steel face between the inner concrete and the concrete surface

 

[racookpe1978]

Well, there's more to look at up the top of the "tank" ...

When the floor compresses the bottom steel - as you point out, but ONLY if it hits the floor perfectly flat - the top of the tank and its internal concrete will continue "down" as the impact shock wave slams up. Then that impact wave will hit the top of the tank, and will then rebound and try to force the upper concrete inside "out" spreading the walls, and the lower part of the concrete "out" at the bottom. Since the weight of concrete increases from top to bottom, the lower corners are going to get stressed most.

The concrete is not cement "dust" and has a modest amount of tension strength. (It will be able to crack though under impact, and the very fact that it is concrete means that it has no "give" and transmits shocks "perfectly" and fits the steel walls "perfectly" tight with no air ghaps.) But I expect the failures to occur at the lower corners. Example, fill a square paper lunch bag with sand and drop it. The failure will not be the bottom of the bag itself, but the lower corners and sides of the bag.

If the bag were filled with a more compressible load like loose soil, then the rebound loads are smaller since there is more room for the soil to compress rather than squish outwards.

 

[Twoballcane]

In any case this is a combination of Kinetics, Dynamics (shock), and Structural. You will have to formulate the equations from these three theories. There is no one all encompassing equation that you can use. However, (not to pick on you and I am not flaming you) the inherit danger of someone doing FEA and not knowing if the results are correct. The hand calculations should have been done first and then FEA so that you would know that you set up your FEA model correctly and the results made sense. If you can not do the hand calcs, what's the purpose of doing the FEA?

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[rb1957]

if you do the hand calcs first, why do the FE ?

 

[racookpe1978]

You've not defined how the 10 mm walled "box" is put together. Those corners and joints are going to be the limiting parts of the structure.

If this is anything more than a classroom/training exercise .. build it, fill it, wait for the concrete to dry, then drop it.

 

[Twoballcane]

Well, the FEA is a second data point to indicate that you’re in the ball park. If one is way off, either one may be wrong. However, doing the hand calcs first will give you an "inside" look of what is going on physically than starting with FEA which is just pressing buttons.

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[rb1957]

if the hand calcs "show it good", why do any more ?

 

[Twoballcane]

I have always believed in checks and balances, especially when a requirement has to be satisfied by analysis (when test is too expensive) during PDR and CDR. It is good practice to have two good data points to reference. I prefer doing the hand clacs first to do scenario iterations and then FEA to both confirm analysis and fodder for slides to management and customers during presentation.

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[rb1957]

and to produce really nice looking pictures ...

 

[jbeckhou]

Take a look at DNV 2.7-1. The standard is free from their website. 2.7-1 equipment requires a drop test.

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