Impact Deceleration

[engpes]

I am trying to determine the net impact force for a falling object has (8x10 structural frame)from 2 inches off of the ground. I know the mass of the frame and I can calculate the energy balance if I can determine the deceleration time.

Is there any published data / constants that can relate the falling velocity & weight of an object to its deceleration time when impacted against a particular material (say wood or concrete)?

May frame is about 5,000 lbs and will be dropped onto a wooden deck. This could also be assumed rigid for simplicity's sake. I am stuck when trying to determine with the deceleration time will be?

Thank you in advance for your help!

 

[zeusfaber]

I don't think treating the deck as rigid is going to help you get to a solution.

Could you make some reasonable assumptions about the stiffness of the deck, then treat it as a simple harmonic motion problem?

A.

 

[IRstuff]

This question has been asked in different forms before. HAve you done a search?

TTFN
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[hydtools]

At near zero drop height, the force of a suddenly applied load is 2 times the applied load.

Ted

 

[3DDave]

You can try picking a deflection and assuming (since it's a guess) that it's a linear spring. F=k*x, and you assume x, and you also know E =1/2 k*x^2, and you know the energy, so voila, you can figure out k and from k what the F at maximum deflection is. Viola! The deceleration time is from d = 1/2 A*t^2, and A = F/m. and you know that x is the distance of the deflection, so .... t pops out.

What is missing, of course, is that the inertia of the platform will not allow it to move as much as the weight might at rest, but you can also assume the deflection will be only of the wood fibers. Some or much of the energy will go into making wood pulp.

If everything is rigid then the time is 0 and the acceleration is infinite, so you need to guess somewhere.