Ski Failure Test

[bigKam]

hi Everyone.

i almost forgot about showing these photos. a few months ago my cousin Kam and i tried to break a ski. the experiment proved to be more dangerous than expected, so don't try what we did at home (see below). in the end, we managed to carefully balance 200 lbs of bricks on one ski before the system collapsed. yes, we expected it to collapse -- in the photo Kam is wearing a helmet and protective glasses for safety .



the ski we tested was a ski that Kelvin and I made but never skied. the ski was made using QCM epoxy and heat-pressed. this was one of the first skis we made using the heated press and it came out with 16mm of camber on each ski. two skis gave 33mm of camber, so i named the skis "33mm".

Kam and i initially thought the ski would break, but it was tougher than we thought. instead, the 200 lbs removed all the camber from the ski, and i noticed small regions of delemination between the glass/epoxy and wood core interface, but no obvious signs of failure in the wood. the photo below shows the untested ski with 16mm of camber. next to it is the ski that was loaded with 200 lbs, completely flat.


anyway, i thought the photos might interest some of you. again, don't balance bricks as shown! find a safer method to test.

[endre]

That's impressive K! it shows in a good way that skis are very hard to break. I did something similar with my car and a piece of ski I built for the purose. the core goes from 12,5mm middle to 3mm, triaxial 850G/m2 glass layup, axson heat cured epoxy, 2000 base and 2mm R48 steel edges.








the piece of ski came out with no visible failure!

[davide]

Endre, that's super cool! Was it plastically deformed?
I have no car, so I can't test it that way.

I did few testing on the material I cut away while trimming the skis: as long the ski, about 1 or 2 cm wide. Indeed, it deforms plastically (like the ski tested by bigKam), but it is quite hard to break.

I suppose a wood/carbon ski would break instead; no plastic deformantion.

[BigG]

A Carbon ski could have some similarity in my point of view. I have been doing some tests on hollow carbon rods and some of them can be bend very far. I think everything would depend on the angle of the carbon fiber.

Geoff

[plywood]

i used some carbon on my skis and i did the same thing as davide.

i also tried to break the material i cut away during trimming...and i had serious problems breaking it. i know it`s said that carbon breaks and fibreglass just gets rammed if put under a too big load. this is kind of right...carbon breaks earlier than glass, and glas also breaks.
if i regard the pictures of your experiments i`d say that there would be no difference between the skis showed and a carbon one. because of the following reason: the "bending curve" (or however you would name it) of the skis has a relatively big radius. i had to bend my pieces a lot more till they broke...i had to force a piece of 40cm of the front section where the core is about 3mm to 6-7mm nearly into a "right angle" (the pieces i hold in my hands were rectangular to each other and i bent the 40cm in the middle with my knees)...well maybe there the construction of the core also has an influence

further i think the problem is not the fibreglass-layer - it`s the core! somehow i`m satisfied that the core breaks first and then the whole system collapses. i saw several broken slalomskateboards...and nearly all of them broke because their core was constructed weak. they had a horizontal laminated core with 5 layers of wood, 2 with grains lenghtwise, abour 1mm thick, then one layer with grains crossways, about 2mm thick and again 2 layers 1mm lenghtwise - and their "breakingline" started in the thick midst layer....