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Hanaldo - 4/17/2021 1:17:30 AM

Well now you're starting to throw in other variables that make it hard to determine what is going wrong, but in this case I would suggest you have tried to do infusion with a resin that is not suitable for infusion. Flat sheet is quite forgiving to infuse, you dont have geometry trapping air as the resin flows around it. And contrary to what you might expect, thicker layups can actually infuse easier and better than thin layups, due to the flow channels created by the fibre crimp. Thin laminates have less space for the resin to flow, so actually require a lower viscosity resin.

When things aren't working, that is when you need to become scientific and repeat the experiment with as few variables as possible, changing things can throw you off finding the solution. I can understand running out of infusion resin, but waiting for more to arrive is probably a better idea than trying to infuse with hand laminating resin and binning all that carbon/glass/consumables/time. 

Release agent is not a concern here, parts are releasing so that is fine. Just a warning though, if you have waxed over the Easyleased moulds, you now need to treat that mould as a waxed mould, you can't put any more coats of Easylease on unless you strip it all off and start again. Wax on top of chemical release agent is ok, chemical release agent on top of wax is a disaster waiting to happen.

So, these last two experiments I would say are inconclusive because of the different resin used. I feel they failed because that resin didn't wet the reinforcement out properly, leading to an extremely lean resin content that explains both the poor surface finish as well as the poor interlaminar adhesion. The previous experiment failed due to bridging. And the one before that failed due to air leaks. Solve each of these issues all in the same layup without running into any other issues, and you will get a good result. Unfortunately this is the learning curve with infusion and composites in general, and at the moment the process is teaching. Its a shame school is expensive, but keep going with it and the process will deliver. 

With regards to your layup and choice of reinforcements, then I would say if it works for you then it works for you and there is no reason to change that unless you want to move to pre-pregs where your choice of reinforcement is more limited to what you can buy commercially. That said, virtually what you said about needing the flexibility of the glass and the stiffness of the carbon is the misunderstanding that most people have with composites. You don't get both properties, you actually can't make a fibreglass structure stronger or stiffer by adding carbon, just like you can't make a carbon structure more flexible by adding fibreglass.

Carbon fibre has an elongation to break of about 1.5%, while fibreglass has an elongation to break of about 5%. So when your laminate takes a load, it doesn't matter if you have 100 layers of carbon fibre with 1 layer of fibreglass or 100 layers of fibreglass with 1 layer of carbon or 50 layers of each, the entire laminate can still only stretch 1.5% before the carbon breaks. The fibreglass will keep wanting to stretch to 5% before it breaks, so if your laminate cops an impact or a point loading that stretches it beyond 101.5% of its total length, then all of the carbon in that laminate is going to break, while the fibreglass is going to keep going. Once the carbon is broken it isn't doing anything for the structure, so you only have the strength of the fibreglass. So to avoid your part flying to bits entirely, it would need the fibreglass to be strong enough to carry the required loads once the carbon has broken, which makes the carbon redundant; OR it would need the carbon to be strong enough that it can carry the required loads without stretching beyond 1.5%, which then makes the fibreglass redundant. A good analogy I heard for it is it's kind of like having a piece of aluminium (your carbon) and trying to reinforce it with a rubber band (your fibreglass). If you take that structure and bend it, the rubber band will bend significantly further than the aluminium but it isn't doing anything to prevent the aluminium from bending. 

There are situations where fibreglass is a superior material choice to carbon. If you have an application where you know a given laminate is going to be subject to loads that stretch it beyond 1.5%, then you have two options: make the laminate stronger by adding more layers so that it takes a higher load to achieve that elongation, which also means a heavier laminate. Or, use a material that can stretch further than 1.5% before it breaks, like fibreglass. 

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oekmont - 4/18/2021 6:26:07 PM

Reinforcing carbon with glass is like reinforcing a steel wire with a bungee rope. Before the bungee rope is stretched enough to really produce any significant force, the steel wire will be already way past it's elongation maximum. The combination will still be just as stiff and strong as the steel rope, but with the additional weight of the bungee cord.
Either a glass or carbon sandwich might be the solution.

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Hanaldo - 4/19/2021 1:12:46 AM

Based off your measurements I would estimate you need 700-750g of resin. 

Fibre:resin ratio should be ~60:40, so you need about 450g of resin (I like to round up) for your 650g of reinforcement. 

Mesh will take about 700g per square metre. Peel ply is pretty negligible unless you are doing bigger infusions, its about 80g/sqm. By rounding each calculation up, I find you tend to compensate enough to not worry about calculating for peel ply, and hoses, and then depending on infusion size I might factor in a little bit of wastage in the bottom of the pot as well.