This user has no status.
This user has no status.
Well-Known Member
Today I put a rubber and TT ball in our hydraulic system to watch how the force increases as a function of compression.
Why bother? Because I want to know if rubbers really bottom out.
I can calculate the energy that the ball has when it hits the paddle. Eventually the ball stops relative to the paddle. At that point the rubber AND ball have absorbed all the energy. That is equal to 1/2K*distance^2. This test allows me to calculate the spring constant K. Actually the "spring constant" isn't really constant. It is non-linear.
Some of the results were as expected. At first the force increases slowly and builds as the more and more of the ball gets pushed into the rubber. I was using Rakza 7 2mm scraps for the rubber and a old Stiga 3 star ball. What surprised me is how far the rubber seemed to be compressed. We compressed the ball and rubber about 2mm or 0.0.80 in. I didn't expect the rubber alone to compress that much without "bottoming" out. Later we squeezed just the ball and again we squeezed just the ball about 2mm or 0,080 in. The ball compressed linearly until the ball was compressed close to 0.080in or 2mm and then the force didn't increase linearly any more. The ball didn't break and it seems to be OK. I need to test a plastic ball as they don't seem to compress as much as a celluloid ball.
So now the question is what was compressing during the first test. Obviously it is the rubber AND the ball. I need to test the rubber by itself without the ball. The top sheet compresses too so there are 3 springs in series. The top sheet the sponge and the ball.
I have video and recorded data. It is crude. The load cell I was using when from 0 to 5000 lb and I was using only a small fraction of the load cell rage. We need to obtain a load cell that goes up to about 100 lb or 500N. 1lbf = 4.45 N. My position sensor was calibrated in inches. What is old is the sensor naturally returns position is microns but the people here are used to inches. Also, I need to get a better valve. We have them but it was not on the machine at the time.
I wanted to test just the rubber but it got accidentally smashed. The machine can apply forces to 4500 psi.
What I found encouraging is that the models I have been using were in the ball park given the assumptions I had to make.
pictures and videos to come.
Why bother? Because I want to know if rubbers really bottom out.
I can calculate the energy that the ball has when it hits the paddle. Eventually the ball stops relative to the paddle. At that point the rubber AND ball have absorbed all the energy. That is equal to 1/2K*distance^2. This test allows me to calculate the spring constant K. Actually the "spring constant" isn't really constant. It is non-linear.
Some of the results were as expected. At first the force increases slowly and builds as the more and more of the ball gets pushed into the rubber. I was using Rakza 7 2mm scraps for the rubber and a old Stiga 3 star ball. What surprised me is how far the rubber seemed to be compressed. We compressed the ball and rubber about 2mm or 0.0.80 in. I didn't expect the rubber alone to compress that much without "bottoming" out. Later we squeezed just the ball and again we squeezed just the ball about 2mm or 0,080 in. The ball compressed linearly until the ball was compressed close to 0.080in or 2mm and then the force didn't increase linearly any more. The ball didn't break and it seems to be OK. I need to test a plastic ball as they don't seem to compress as much as a celluloid ball.
So now the question is what was compressing during the first test. Obviously it is the rubber AND the ball. I need to test the rubber by itself without the ball. The top sheet compresses too so there are 3 springs in series. The top sheet the sponge and the ball.
I have video and recorded data. It is crude. The load cell I was using when from 0 to 5000 lb and I was using only a small fraction of the load cell rage. We need to obtain a load cell that goes up to about 100 lb or 500N. 1lbf = 4.45 N. My position sensor was calibrated in inches. What is old is the sensor naturally returns position is microns but the people here are used to inches. Also, I need to get a better valve. We have them but it was not on the machine at the time.
I wanted to test just the rubber but it got accidentally smashed. The machine can apply forces to 4500 psi.
What I found encouraging is that the models I have been using were in the ball park given the assumptions I had to make.
pictures and videos to come.