Correct resin, gel and fibreglass.

The central part is black as I ran out of fibreglass :-)

Agreed, the ribs were not necessary, hindsight is a wonderful thing :-)

Total of 8 layers  with 6 under the reinforcement and two on top.

Drawing below shows the construction and deformation cause, which was a combination of pressure differential and lack of post cure IMO. Without the reinforcement the lack of post cure wouldn't have been an issue. If I had post cured I might have gotten away with it.

If I had just bagged the underside the pressure would have been constant on the other side and the deformation wouldn't have happened. Oh, well, hopefully I can rescue the bonnet.

It's an interesting mould, but in my opinion that ribbing structure is totally unnecessary as well. That mould would be plenty stiff just from those parting barriers.

Anyway, I agree with oekmont - the pressure differential isn't the cause of the print. If it was, the mould surface would have blistered outwards, not collapsed inwards. And even this would have been extremely unlikely unless the mould is only one or two mm thick - a regular thickness mould of 5-6mm would quite easily withstand that pressure differential.

Unless of course, as oekmont mentioned, the mould couldn't handle the temperature. Whether that's due to too low a Tg, or just not having had a good enough post-cure prior to attempting this cure. I'd say this is almost certainly temperature related.

Sorry to hear and see that. But this would have happened with any other bagging technique. It looks like your mould wasn't tempered high enough, or your mould resin just isn't suitable for the temperature.
Why is the central part of your mould black? did you use the same resin? What material did you use for the stringers? What is the layup of your mould, especially underneath the stringers?

Making a prepreg carbon front clip for my Lotus Elan. So far so good.



Mould with the reinforcement that caused the problem. I bagged the whole thing. This resulted in a differential pressure between the inner surface and the outer skin under the reinforcement which resulted in the mould sinking under the pressure!