# Rubber compression strength question

1. Jul 21, 2012

### cliffd

Need help in determining the impact force strength of a door stop rubber. It is a urethane rubber formed in a triangular shape. I used a 50t press with a 2" round shaft to compress rubber product and it required 100 lbs of force to compress. I beleive this worked out to 18.75 ft lbs to compress rubber. My question is : if a 36" x 80" metal door weighing 200lbs is swung open, what type of impact force can this rubber take? (contact surface of the rubber is 2" x 3/4")

2. Jul 21, 2012

### CWatters

I think more info might be required, such as how fast the door could be moving.

3. Jul 22, 2012

### cliffd

If my calculations are correct, the circumference of a 6 ft circle would be 28.26 ft. A 3 ft door would basically swing 90 degrees from the closed to the open postion where it would contact the door stop. If we divide the total circumference of a 6 ft circle by 4 we should get the distance travelled by the door from its closed to its open position. If it took 1 second to open the door, that would be approximately 7 ft/sec. It takes less than one second to open a door.Let's use 10 ft/sec and 20 ft/sec for calculating.

4. Jul 23, 2012

### CWatters

Because it's a hinged door you should really treat it as a rotating body so it has a moment of inertia and then energy stored in the door will be proportional to it's angular velocity rather than it's linear velocity... but you could approximate and do it the way you have..

Energy stored in the door

= 0.5 x mass x velocity2

Energy dissipated in the stop

= Force x distance

so equate these two..

Force x distance = 0.5 x mass x velocity2

Force = 0.5 x mass x velocity2/distance

"distance" is the amount the stop is compressed.

Probably need to add some sort of safety margin? Factor of two?

5. Jul 23, 2012

### cliffd

So what type of force in lbs would this door produce travelling at 10ft/sec or at 20ft/sec?
How would this compare with the compression resistance of the door stop rubber? Would the door stop rubber be able to handle the impact force created by the door at either speed without completly compressing together (front portion of rubber stop would need to travel approximately 1 1/4" to contact rear portion portion of rubber stop)