We’re trying to build composite (carbon fiber) structures that have flexibility to them. The epoxy resins we’ve tried are much too brittle. Can anyone recommend a resin type or additive to make our composites flexible?
Try this epoxy resin system and tell me how it works out for you… i have used it and it is pretty flexible even after full cure.
Aeromarine 300/21
How much flexibility do you need? Carbon fiber can’t go through too much strain.
If the resins are not flexible enough you dont have to use fibres. Try to change to other plastics.
What do you want to do?
polyurea or polyurethane
polyprop or polyethylene also for thermoplastics.
There are very flexible epoxy resins, with a strain up to 400%.
Sicomin SR8150 is one of them. For instance the bumpers on the Paris Dakar cars are made of them. If they hit something, the bumper just flexes, but does not break or damage.
It is better to use aramides as fiber, though.
Carbon fibre isnt really the right re-inforcement to use if you need a flexable item! Carbon fibre is normally used to give a stiff component. Or the same stiffness as a grp component for a much lower weight.
I am guessing that you are using carbon fibre more for looks on this item than any other reason? What is the item that you are making?
Do you supply that resin? I guess time-out does also, they say a 80-110 strain, But I haven’t seen datasheets yet.
What is the Tg? We need a semi-flexible contra-mould, the ones we use now crack on the edges.
I have used the Aeromarine 300/21 and it does the job. It is flexible to a degree, say, more than West epoxies which is really the only one I can compare it to as I am far from an expert. I am using that Aeromarine stuff for motorcycle fairing fabrication where you want a little flex to them.
yes… i would c certainly look into your engineering, Carbon is used as a stiffener in structures, using Innegra or other aramids would improve the flex, particularly matching it to the resin characteristics
I have to disagree with the whole carbon isn’t meant to bend pile on. While i make no claim to be the master of all things carbon i could name any number of things made of carbon that are built to bend and flex (such as masts, golf clubs, surfboards, snowboards and skis) and matching the desired bend characteristics to your resin system is very important.
Lets not forget one of the best uses for Carbon, Prosthetic limbs.
It all depends on the amount of flex needed.
A limb or a mast will see only limited flex, where for instance a bumper of a car will see loads of flex, when a rock is hit. (at impact, the bumper might flex locally more than 20 cm (8 inch).
Same for roll-up mast moulds, used for small masts. (Europe, Finn). The aramide/flexible resin mould is able to fold open completely, and fold close again to form the mast.
as a Professional surfboard builder for 25 years, carbon on surfboards is used predominantly as a gimmick and occasionally as a stiffener.
Innegra is best for impact resistance and neutral flex properties…
Did they really photoshop him on a track? How hard would it be to take a picture OF him on the track? sigh
does anyone have some info/datasheets on flexible resins? I found a can of Sicomin SR8150, but the Tg I found was around 17 degrees celcius. With a recommended postcure of 60 degrees celcius for some hours I would expect it to be around 70 degrees celcius(and what the hell, postcuring above the Tg destroys parts…). What happens on elevated temperatures, will the product show print from the fibre and the surface it is vacuum bagged on?
With such a poor TG, yes… Print throughwill beaproblem. More importaintly, so will structural stability. Correct me if I am wrong.
I don’t really need the structural part, I need surface quality and flexibility, for use in a moulding system (much like the masts herman was talking of.)
The problem is, the part is prepreg, so we need at least 65 degrees celcius to cure.
Did some tests, we have some finished products, but to build a mould for every product will be very inefficiënt.
I have laminated some testpieces today, aramid with high Tg resin we use for normal moulds, and SR8150, the flexible resin. I’ll do some testing tomorrow, and report back 
Also testing some silicons, but rubbers will act as a liquid under pressure, so the surface quality will depend on the surface itself, so not really flat when used with fibres 
How flexible do you need this part to be? Did you write that earlier and I’m missing it?
I have made flexible composite hinges using kevlar and epoxy resin although I intentionally used less hardner than the data sheet suggests so as to undercure the resin and remain flexible. Maybe not be technically correct to an engineer but it my case it works very well and have made around 200 products like this with no failures.