Last updated 07/04/2010

Some of the numbers on the website can be difficult to understand. To help you better understand, I have taken some data from some of the tubes and compared them side by side. This is a discussion on the data shown.

Looking at the data above, you can make these statements:

This is the highest load that the tube withstood. Here we see that the Blue Tube withstood well over 3,000 pounds while the phenolic could only handle about 2,600 pounds. This may lead you to believe that the blue tube is stronger. While it is, that higher strength is not useable. If you look at the graphs, you will notice that the Blue Tube didn't even make it to 2,000 pounds before it began to deform and crush. You can see the line on the Blue Tube graph start to curve away from the straight line around 2,000 pounds. The phenolic made it all the way to 2,500 pounds before it began to deform. The line on this graph is straight all the way to failure. I do not have graphs for every test I've done on the site. But, there is another data point you can use that tells you what the graphs are telling you. It's called Modulus.

Modulus, or "Modulus of Elasticity" is a measurement of a materials stiffness. Using the comparison above, you can see that the phenolic is much stiffer. This means that the material holds it's shape up to a higher load. There is a tradeoff in having a stiffer material. Although the phenolic can withstand more load because it is stiffer, it means that when it does "give", it cracks. This shows that, although actually weaker in use, the Blue Tube is tougher than phenolic. A good example the usefulness of a material's modulus is a rope. Since the modulus of a rope in compression is quite low, no matter how strong the rope is, pushing on a rope doesn't get you anywhere.

On many of the tables, you will see the term "stress" On the above example you see peak stress. Stress is nothing more than (in this case) the "peak load" divided by the surface area. In the case of the tubes, "area" is derived from the wall thickness. The thicker the wall, the more load that the material can handle because of the increased surface area. An illustration is this: We know that carbon fiber tubing is stronger than phenolic tubing. A 3" diameter phenolic tubing with a 3/4" wall thickness could hold as much weight as a 3" diameter carbon fiber tube that only has a 1/16" wall thickness. They both have the same peak load, but the carbon fiber tube has a much greater peak stress value.

Using peak stress as the indicator of strength levels the playing field between samples. This shows the overall strength of the material and can help you chose a lighter tube for altitude records. Of course, using peak stress also makes it possible to compare the materials of the tubes, regardless of the tube diameter. This means that you can compare the LOC 5.5" cardboard tube against the USR 2.6" Glassine tubing.

Note that (in both cases) the PML failure was at the spiral grove. You guys that fill in your spirals with glue my have an added benefit you didn't even realize you had.

The USR whitewall tubes broke much differently than the PML. These tubes fan folded and never actually broke. The stress oscillated as this happened.