Foam Board Strength - A Scientific Test!
- Thread starter DutchRoll
- Start date
DutchRoll
Well-known member
I am using the back of my 3d mill from my testing rig.
- I've attached a Fiskar's cutting mat to the back using magnets so that I can measure beam deflection under load.
- The beam is held on the left side with two 2x4 screwed into the mill frame, and set 2 inches apart.
- Please note that I've changed the beam size from 1.5 inches to 2 inches to make my measurements easier to read.
- Weight cup is an old cookie tin with nylon straps taped to the sides, and can hold 2.2 lbs (1 Kg) of steel washers. Tare weight is 62 g.
- Cup strap is placed 1 inch from end, and washers are slowly added to the cup until the beam fails.
- A bucket with a towel in the bottom is set underneath to catch the cup in case of beam failure.
- I put a 2x4 inch beam of naked Styrofoam in to test my process.
- Beam deflected 0.25" (6.35mm) with just the cup on the end.
- I added in the full 2.2 lbs (1 Kg) of washers, but the beam didn't fail. It just slowly deflected 8" (203mm) downward without snapping.
- After the test, the foam at the attachment point crushed on the bottom, and the beam now deflected 1.25" ( 57.15mm ) downward.
DutchRoll
Well-known member
Continuing the experiment, I created a 2"x20" test beam from Ross foam board to verify the testing methodology. Beam was cut from standard white Walmart Ross foam board, and assembled with a spiral fold over (to remove any A/B structural bias) and hot glue. Contrary to my expectations, the beam did not fail catastrophically, meaning it didn't split at the joints or twist along it's length. Instead, the beam's end in the fixture distorted as it crushed over the edge of the lower 2x4, which acted as a fulcrum, and eventually the beam slipped and/or tore out out of the fixture. (the cup bearing end didn't distort under load as it was held it place with 3" of tape)
FYI - I am only testing static loads at this time - dynamic loads in the form of sudden g-forces due to wild maneuvering are harder to test for with this rig.
| Beam was first mounted flush with end of the 2x4 fixture, and held in place with a friction fit. The Fulcrum point @ 1.5" (38.1mm), cup was 2" in from the far end. 1/4" (6.35mm) Deflection at 11.15oz (317g). Beam slightly crushed at fulcrum and slid out of fixture at 25oz (719g). Moved fulcrum to 2", and beam crushed and slid out at 39.4oz (892g). |
| First fulcrum end - you can see the deformation on top and the wrinkling in the paper on the side where it crushed as the unsecured beam rotated in the fixture before slipping out. |
| Next I tried to secure the end so that it couldn't slip out. I flipped the beam around, taped over one end with standard clear packing tape, and slid a skewer through at the 1/2" (12.7mm) mark to anchor the end in the fixture. Fulcrum was set at 2" (50.8mm), and weight was applied to cup. At 44.9oz (1275g) the skewer ripped free from the end, tearing through foam, paper, and tape, until the entire beam dropped out of the fixture. |
FYI - I am only testing static loads at this time - dynamic loads in the form of sudden g-forces due to wild maneuvering are harder to test for with this rig.
Similar threads
