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Thin laminate toughness - single or multiple (woven) plies?

Thin laminate toughness - single or multiple (woven) plies?

Thin laminate toughness - single or multiple (woven) plies?

Hi All,

I'm a mechanical engineer (Automotive) of ~15yrs, looking to establish my own enterprise, designing and manufacturing high-end wheels for the road cyclist.

I'm in the proof of concept / attribute prototype phase of my project, where I have functional hardware fundamentally performing as I would hope. I'm still fairly green to composite design, analysis and testing (enough knowledge to be dangerous!)so I have elected to conduct an iterative approach to defining the laminate(s) rather than analysis based (other than back of napkin stuff) due to:

- Limited analytical competencies specific to composites (& lack of appropriate software)
- Flexibility in tool to accommodate variation in ply count and schedules (to some degree)
- Fairly low cost and ease of manufacture for test components assemblies (2pcs CNC'd heated Alu mold, pressurized bladder for consolidation - up to 10bar)

I'm currently looking for the best laminate definition as a starting point for my design development and verification, pretty much just based on reverse engineering competitor products (not plagiarizing - just bench-marking!), and my understanding of good composite practices.

I have a fairly ambiguous question relating to the faired section of the wheel rim (visible part, not the tire bed part). The Current construction is a thin laminate, nominally 2 plies of 2twill 200gsm HS carbon toughened epoxy prepreg, reinforced locally (additional 2 plies), where the carbon spokes are bonded, tangent to the sidewall. Warp & weft run @~+/-45° to the radial direction for both primary plies. Tightest internal radii is R3.0mm (unavoidable), and I'm using a PTFE intensifier to help achieve a satisfactory laminate quality in this area. All other radii are >R8.0mm.

The finish product needs to be as tolerant as possible to impact damage from road debris or in the event of a crash etc.

My question is: as inter ply delamination often occurs after impact damage, would a more impact tolerant structure be made using a single 400gsm ply in place of 2 x 200gsm plies? I obviously cant avoid using multiple plies around the reinforced areas, but these constitute <20% of the exposed surface, so perhaps less likely to be effected. Also, with respect to fiber fraction volume, whilst low mass is advantageous, should I keep more resin present to increase the toughness (I guess; how much toughness is enough...)

I'm obviously not working to any particular numbers here, just want to ensure I start out on the best possible road to successfully complete DV testing, and create the best possible product.

Any help, advice or though provokers would be warmly welcomed.

Thanks in advance, Jon.

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