Puncture Testing

This is testing of some very light materials, when considering the subject of building super light PDRacers.

Picture to the right -- Puncture test setup. The square of 3/8 ply is only to hold up the scales for the pic to be taken. The gray patch on the 1/8 ply test piece is a 1/16" layer of epoxy

Here's the setup: a test piece of 1/8" ply (door skin) is clamped to the edge of a table, then an awl placed on it, then a bathroom scale placed on the awl, then weight applied to the scale until the awl punches through the plywood. The pounds of pressure being applied a the time of punch-through is noted.

I did this two times each with a piece of 1/4" corrugated cardboard, a 1/8" piece of door skin plywood, a piece of door skin with 1/16" layer of epoxy coating on it, and a piece of 1/4" inch B-C exterior plywood.

Here are the results:
Material 1st Time 2nd Time
Cardboard 8 lbs 8 lbs
1/8" Plywood (door skin) 39 lbs 36 lbs
1/8" epoxy plywood 62 lbs 65 lbs
1/4" plywood 115 lbs 120 lbs

So 1/8" ply is 4.7 times as puncture resistant as corrugated cardboard but an epoxy coat increases puncture resistance to 8 times that of cardboard. However, 1/4" ply is 14.7 times as puncture resistant as cardboard.


Final Puncture Test From left to right: 2 x 1/8", 1/8" with cloth coat, cardboard with cloth coat Curiosity led me to try a puncture test on a section of 1/8" doorskin that was coated on one side with Titebond II-soaked cloth. And as a reference I tested a Titebond II-soaked cloth coated section of cardboard. Also since I've seen it proposed to laminate 2 sheets of 1/8" to achieve the strength of 1/4" ply, I tried a section of that.

Here's a photo of the 3 types of material. The cloth is 50% combed cotton/50% polyester, 200 thread count weave, applied with Titebond II. I let the Titebond II dry for 3 days.

Here are the results:
Material 1st Time 2nd Time
Cloth Coated Cardboard 15 lbs 14 lbs
Cloth Coated 1/8" ply 48 lbs 45 lbs
2 x 1/8" ply 103 lbs 99 lbs

The glue-soaked cloth does increase the durability of material as it did with the cardboard and with the 1/8" doorskin. Laminating 2 1/8" sections of doorskin failed to achieve the strength of factory produced 1/4" plywood.

As a side note, the cloth easily peeled away from the cardboard because a thin outer layer of the cardboard easily goes with it. The cloth on the doorskin, however, was tightly bonded and I couldn't peel it away by hand strength. The combination of 1/8" plywood and a cloth coat, plus some additional strength from paint, is something I would consider for hull material.

Tim C