I am in the middle of a large project as an undergrad mech. engineering student and my team and I are having some modeling issues. Here is a description of our task: We must modify the design of a digital spool valve for a company. We have a spool, and 2 electro-magnetic endcaps that the spool moves back and forth between. When the metal spool hits the metal endcaps, there is an unacceptible bounce from the impact force. Now the problem is more complex then this, but on a basic level for a solution we would like to change the materials of various components of this part and have the impact be absorbed. Herein lies the problem, we need some equations to model an inelastic collision, but standard equations will not work. We have plenty of information on the current performance of this spool (ie: magnetic force vs. distance graphs, materials and weights, velocities before and after impacts ect...) It would be nice to have some equations that have material properties becasue we could analyze the efffects from our material changes. Does anyone know of any equation that relates an impact to material properties? I've done some research into the Hertz impact theory, does anyone have any more info on this? Thanks in advance, Alex T.