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Thread: Ski Plate Flex
10-11-2004, 05:08 PM #1
Ski Plate Flex Project
Okay, Since I'm bored as hell:
Here are some ski flex calculation results with different Plate configurations:
I used a sidewall construction ski:
- Ski width at 98mm, height at 15mm
- 1mm thick fiberglass*
- 3mm wide ABS sidewalls
- 2mm UHMW Base
- 1mm topsheet and edges- determined to be neglible towards flex
* approximated strength - still looking for correct value.
- 8mm thick UHMW plate
- Ski has constant profile (i.e. straight ski)
- 300mm Boot length
- Skier weight = 90kg (200lb) = Boot Load 45kg*9.81
- The ski length is taken at 0.8m (tips and tails much smaller profile and not effective)
Ski deflection @ center is 6.29mm
1 peice plate +ski deflection @ center is 2.85mm
- plate is 500mm long x 70mm wide (2.75in) x 8mm thick
2 peice plate +ski deflection @ center is 3.98mm
- 2 plates 200mm long (8") x 70mm wide (2.75) x 8mm thick
- plates are 100mm apart
Note that these are just estimated numbers, since there has been serious assumptions. I'm gonna try to work these numbers more to determine a more accurate model, to also gauge telemark forces effecting the flex. If anyone has any questions shoot 'em at me, and I'll try to explain them here.
This is gonna be an ongoing project, any recommendations, ideas where to go, let me know
Last edited by EstoBum; 10-11-2004 at 05:13 PM.
10-13-2004, 09:06 PM #2
Got your pm, estobum, but without a detailed ski construction (length, core shape, tip, tail stiffness) to base this setup upon, everything becomes one big variable, doesn't it?
Also, with the load of a tele turn being placed more predominately on the toe, the load profile shown is not aplicable, is it?
I printed your pm question and will get you an approximate value for the fiberglass next week when I'm at the shop.
10-14-2004, 11:38 PM #3
Problems, what kind of core material? And what is the oreintation of the fiberglass, and what order are the different directional plys liad up? what guage is the fiber etc etc. Check out the Handbook of Composits by S.T. Peters publsihed by Chapman and hall the elongation at the breaking point of most fiberglass fibers is aproxiamtly 4.8 % but this is complelty variable upon the above variables and the resin used. Teh actual value can be calculated from the laminte equations, but this is very long and difficult to do, it is a extremly complex equation.
10-16-2004, 11:41 PM #4Registered User
- Join Date
- Oct 2003
Am I correct in guessing that you assumed that the plate was able to slide freely on the ski at both front and back of the plate? i.e. all the plate can do is exert downward forces on the ski, but no torques, right?
Also, it looks like you are assuming that all the reaction force from the snow is concentrated at just two points, one ahead and one behind the plate, not distributed continuously along the length of the ski (or edge). Is this correct?
It's not clear from your diagram what assumption(s) you made about the length of the plate compared to the length of the boot. What did you assume?
When you went to the two piece plate, I don't see any description of your assumptions, particularly, exactly how each half of the plate is attached to the ski, and how the boot is attached to each separate piece of the plate. If it's the latter, did you assume some attachment that looked vaguely like a binding with a forward pressure spring?
Did you do your calculations analytically, or did you run your models through some finite-element solver? If so, which one?
Finally, if you want to separate out the effect of the plate, why are you getting all involved in modeling the ski itself? Why don't you just assume a beam (with no internals) that has a stiffness equal to the measured stiffness for the waist area of some real-world ski, and then look at the effects of different mounting of the plate, different plate materials, different plate length and thickness, etc. on the flex?
Tom / PM
Last edited by PhysicsMan; 10-17-2004 at 12:00 AM.