Impact force

[329moss]

How can i estimate the impact force generated by an object, for example a object with mass of 2kg falling from a height of 1m on a fixed end beam. Will it be possible to work out the impact force generated without requiring any experimental observations and without knowing the time interval over which the force was applied.

Any suggestions?
Thanks

 

[kingnero]

This has been covered before, for instance in thread 290673.
Without knowing the time or the deflection, and without doing any experiments your best estimates will still remain guesses.

 

[rb1957]

you could model the problem ... you're transferring KE from the falling mass into strain energy in the beam, and back again (as the beam rebounds).

 

[TXStructural]

For relatively light objects at low velocities (2 kg falling from 1 meter qualifies), you could probably take the load and deflection as those resulting from an object of twice the weight. It is roughly equivalent to Timoshenko's observation that axially-loaded rods which receive a suddenly-applied load elongate twice as much as a when a static load of equal weight is on the rod. The extrapolation is that applying a load that is twice as heavy simulates this effect.

Higher velocities,and intuitively I'd say that a very heavy object relative to the mass/inertia/resistance of the beam, confounds this approach. At some point you have to get to energy equations and the local yielding of materials. I had a client who was accidentally asking about objects falling at terminal velocity. When I told him that they would penetrate the steel, he realized that he had not asked the right question, since the objects would be falling less than 10 feet.

 

[tdstructural]

I agree with TXStructural (see above). I've always used 2 times the weight.

 

[BAretired]

You can calculate the potential energy at release and the kinetic energy at the bottom of the object's travel. You cannot calculate impact unless you know the magnitude of the beam deflection plus indentation (the object's travel after initial impact).

This link gives an answer to the problem if you can estimate the beam deflection.

http://www.livephysics.com/tools/cl...ated-to-impact-force-from-falling-object.html

BA

 

[329moss]

TXStructural, do you have a reference (i.e. book) to Timoshenko's observation that axially-loaded rods applied with a sudden load elongate twice as much in comparison to that of a static load.

Thank you also thanks to everyone else who have replied.

 

[ACtrafficengr]

I recall seeing that in my Mickey Mat textbook by Gere & Timoshenko back in the late 80's.

http://www.google.com/products?q=Mechanics+of+materials,+Gere+and+timoshenko&hl=en

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/