Project Description:
The machine part below is part of an industrial stamping process. A force F is applied on the pad at the top position, the pad moves down 3.0 inches through the air and the rod impacts the floor. The force and pad continue to move downward against the spring a distance equal to the maximum spring compression.
At the top, the force is just moving through air so the pad doesn't experience any load until the rod movement stops at impact. Then the force starts to act on the pad due to the resistance of the compressed spring. After it reaches the lowest position, the spring pushes the force back up to begin the process over. During the travel up, the load on the pad decreases from a maximum at the lowest point where the spring displacement is maximum and it goes back to 0 at the top where it started. Then the process repeats. In other words, the force on the pad goes from 0 to maximum and back in a cycle.
Assume an 80 lbf force is applied which is split up between the two sides of the pad and that the spring constant is 125 lbf /inch.
Design an aluminum cantilever beam section on which the force is applied to withstand impact movement up and down 3.0 inches off the ground and back for a life of 8(104) cycles.
The pad should be a reasonable size (less than 5 inches on each side in length and between 1 and 3 inches wide) and a thickness determined by your analysis. Assume a safety factor between 2 and 3. Choose a reliability greater than 99%.
Use a 2000 series wrought aluminum alloy*. There is no endurance limit for Aluminum alloys; it's not like steel. So you have to use a modified fatigue strength based on a test value of fatigue strength for Aluminum of 5(108). The equation for b and c in Sf is different than for steel. Also, notch sensitivity q is on the Aluminum curve.