Need some material/layup advice!

General Composites Discussions Composites Talk
#1

Alright, so I’m looking at producing composite shin guards for slalom ski racing (pic http://www.mikejanyk.com/gallery/001.jpg )…I’ve done a few one-off models over the years, and now I have a set of very high-quality molds in the works, and I want to build a prototype set from the molds soon for on-snow testing in the coming weeks.

Now, here’s the thing…as you can imagine, these things see a tremendous amount of impact force, over a very small area…so much that my last set (2 layers cf with 2 or 3 layers e-glass core in a PER matrix) have actually fractured clean through in a few spots…the whole thing is super flexible now, and pretty much useless.

My plan for the new design is to use kevlar…with possibly an s-glass core to keep costs down, use more layers, I’ve now got West System epoxy, and I’ll be vac bagging the whole affair to reduce weight and add strength.

My question…any particular recommendations for weight/weave of kevlar? Is my s-glass core idea worth doing? How many layers of each, and what weight of fabric should I be going after? Any other tricks I can use to help stiffen these things, while at the same time keeping 'em light and cheap? Thanks, this place is great!

#2

I would think kevlar/carbon hybrid would be ideal for this application. But if cost is a major factor, and you are looking for high strength low weight, then some sort of thermo-formed plastic would probably be a better choice than what you have in mind at the moment.

#3

Little update: I have a line on some Spectra 900, in a 15.5 oz weight…could that be a good idea for a core material?

#4

Wonder what price you intend charging for this product, and is it likely to be cheaper than whats already available?

If you are looking at a market where there are other competing products already, then your product either has to a lot better than the competition, or comparable and much cheaper.

These are things that are well worth looking at before going into various options regarding materials etc, as unless you are able to produce a better or cheaper product, then the potential of this doesnt seem that great.

#5

Vacuum formed Polyproplene or better yet PC (Polycarbonate).

#6

I would imagine similiar products are going to be made out of some sort of plastic, which makes unit cost very cheap, and probably pretty durable.

I cant see how it would be possible to make a laminated part, which would come anywhere near plastic in commercial terms?

#7

I’m looking at this from a high-end perspective, as the low end products (sub-$100) are made of an ABS plastic, which in the cold WILL shatter upon impact, and quite consistently, at that.

Polycarb variants of these guards go for between $150 and $180, and are more durable, however, I’ve been getting reports that the gates seem to ‘drag’ on the polycarb surface, which results in the guard twisting on the leg, and possibly causing some slowing of the skier.

The GOOD carbon fiber ones are MSRP’d at $370 and up.

Thusly, I see a niche in the local marketplace, and I have a few ideas to reduce friction between the gate and the guard.

I’m not looking at this as a long-haul, big money opportunity…but more of a personal challenge, and if I pull in some beer money…great!

#8

Sounds like it could be quite profitable, so well worth having a serious look at. But think if there are concentrated impacts involved, it might be better to look at kevlar/carbon hybrids, which are available in different colours, which may well help with marketing?

#9

I couldn’t agree more! The one constraint of course is cost…so I’d be looking at using kevlar/carbon hybrids as the outer cloth, for it’s cosmetic properties, then making the inner layers from a cheaper alternative.

#10

On the PC use the scratch resistant ones as they are much more slippery! And the secret on any sheet plastic, wax it with Plastics wax!

ABS is very weak as it is a modified styrene.

#11

Sadly if you back kevlar/carbon with glass, then its going to pretty much mean the performance of the final part is going to be reduced drastically!

You need to decide whether you want to make expensive hig end products that actually work, or expensive high end product that looks nice, and doesnt work that well.

#12

Ah, makes sense. Here’s the new layup plan I was contemplating

Face fabric (Likely a carb/kevlar hybrid)
2x Kevlar
2x Spectra

Thoughts?