
Re: Impact Force
FredKohlhepp Mar 5, 2012 8:10 AM (in response to ptc4168940)According to Roark, it's an energy balance.

Roark on impact.xmcd.zip 5.1 K


Re: Impact Force
wayne Mar 5, 2012 8:54 AM (in response to ptc4168940)I agree with Fred, to expand a bit
Equate the kinetic energy just prior to impact to the internal strain energy stored at the maximum displacement, when the kinetic energy is 0.
The elastic strain energy stored is equal to the work done, 1/2 times the force times the maximum displacement
You could apply a load to get the stiffness, and then solve for the dispacement using the above.
Include the potential energy if required.

Re: Impact Force
ptc4168940 Mar 5, 2012 9:21 AM (in response to wayne)I have multiple materials deforming and tearing. I am at a loss as to how to even begin those kind of strain energy calculations.

Re: Impact Force
wayne Mar 5, 2012 9:45 AM (in response to ptc4168940)I don't now about tearing and plastic deformations, that would be a huge undertaking, but you indicated using a factor of safety, one buy product of the safety factor is that you can normally use linear elastic analysis.
As I indicated, the elastic strain energy stored is equal to the external work done, which is much easier.
Internal strain energy stored = 1/2*Force*displacement, which is 1/2*K*d^2 where K is the elastic stiffness corresponding to the location and direction of the force F.
So, do a model, apply a load F, determine the displacement and then the stiffness. Then euqate to the Kinetic energy and solve for the displacement, then the force F=K*d (a dyanmicallly amplified equivanlent force) and solve for the resulting stresses.
You might be able to find classical solution (like from Roark), or and conservative simplification, but if not, you may need to use an analysis program to get the stiffness. (Or possibly do the entire problem)
The equation that Fred referenced can (and probable was) be derived using the above.

Re: Impact Force
FredKohlhepp Mar 5, 2012 11:27 AM (in response to wayne)As a simple first step, calculate the deflections and stresses due to the static weight of the projectile at the impact point. Then the ratio of deflection and stress at 290 mph to static is sqrt((290mph)^2/(g*static deflection)).




Re: Impact Force
ptc4023856 Jul 7, 2012 10:44 AM (in response to ptc4168940)It is stored energy with in a damper