Testing Carbon Fibre before I commit – Part 2

So, here is the raw results file:

raw data

I’ve kept it there in the spirit of honesty, but the following distilled data into the graph is what really matters:

new graph


So the numbers that matter are those on top of the line – each of those is the number of KG force required to deflect the part by a given distance. You can correlate the colour to the number to the data in the top chart (click through for details)

Finally, there is the density/deflection ratio, which would show the ideal performing part if absolute strength wasn’t the most desired outcome.



There is a trade-off between core and layers, which is what would be expected. What actually surprised me the most was the difference a core makes.

The top line has two variables set – 4 layers of CF (rather than 2), and a 10mm core, rather than the yellow line, which is 4 layers and a 6mm core. The third highest line is the darker blue line, which is 2 layers and a 10mm core.

So, it’s layers over core but again, there’s a trade-off. The red line is 4 layers over a 3mm core, and you can see it yielded really quickly at 3mm with a very low amount of force (well, 98kg of force). Without doing any statistical analysis, I am observing that each 3mm of core seems to give me an extra 100kg of resistive force before yielding. However, I don’t know how far that scales.

Finally, you can see that there are a selection of flat lines near the bottom, and they are parts made without core. The seem to bend a lot and not yield. For my purposes though, they’re not suitable. Parts 6 and 7 (four and two layers), deflected up to 7mm without yielding, but weren’t much use to me.

As the thicker parts started to yield, we could actually hear them crack (quietly). I’m assuming that’s the fibres snapping. As such, the moment it starts to happen the part is compromised.

4 thoughts on “Testing Carbon Fibre before I commit – Part 2

    • you know – that’s a crucial question, and not one I put in the conclusions. Answer is yes, and here’s how:
      For the floor, full thickness, 10mm core and 4 layers of 600 gsm.

      For the transmission tunnel sides, same carbon, 3mm core. I don’t need huge strength in bend, but need lots of force sent back to front in case of a rear end shunt.

      side panels, no core needed – I am keeping the 25mm chassis rails, so by the time I skin the panel both sides, and graft a core in, I will have the equivalent of an aircraft stressed skin.

      So, on each side there will be a different layup. If I hadn’t done this experiment, I would have probably gone for a 10mm core and same thickness of CF all round, and wasted assets for no gain.

  1. Dude! I love what you are doing! I am quite jealous as I’d love to have a play with some carbon but I’m not in a position to at the moment. You’ve got a great project to focus your efforts on 🙂 You blog makes for great reading, think I’ve pretty much been through the whole thing now!

    Correct me if I’m wrong but I think “density” in your two tables is in fact specific volume? So the meaningful result in the second table would be the 2nd and 3rd columns multiplied rather than divided, which would result in your samples ranking in the same order regardless of whether you were interested in absolute strength or strength per unit mass.

    I could have course got it completely wrong and if so please ignore me and accept my apologies! Either way, good luck with the rest of the rebuild.

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