+x

 

Warren (Staff) - 3/25/2019 5:10:50 PM

The problem you have is not that many people are using a balsa core, especially in the more technical composite processes.  Sure it is more common in hand layup  on rc aircraft etc but not so common on carbon composite infusions.

Ignoring the balsa or assuming it is sealed and therefore has a negligible  resin uptake may be more sensible to getting a answer at  least to start with.

In this case you also need to assume the same basic layup with same fabric weights.

Like for like I would expect  the lightest layup to be pre-preg, followed by resin infusion, then wet lay vacuum bagging with, finally, wet lay up  as the heaviest.

This is mostly down to the fibre resin ratio achievable in each technique.  There is some overlap with all of them, eg a resin rich pre-preg part may be  slightly heavier than a  relatively dry (but still structurally sound) resin infused part.  A well vacuum bagged wet lay up can be almost as light as a fairly resin rich (for cosmetic reasons) infusion.   Some expert wet lay laminators can get their parts almost similar weight to resin infused - all down to skill and experience.  So there is cross-over but generally the Fibre resin ratio changes with each process.

Typically in a out of autoclave  pre-preg part you would be around 60:40 fibre resin ratio  - some fractionally dryer.
A resin infusion you always aim for 60:40  and most typical layups can get reasonably close to that , in practice I have seen a lot around 55:45 or a smidge closer to the ideal.
Wet lay  and wet lay vacuum bagging is typically starting on the heavy side at 50: 50 although with a bit of experience you can get it closer to 55:45  with careful vacuum bagging.  Complete newbies tend to be quite resin rich in their wet lay ups so could have an even higher resin ratio.

That is all fairly "broad brush" figures to get most people started. 

Without testing of your  specific core materials, you will struggle to find specific  data on the impact of the balsa core because, I just don't think the data exists or is not common enough to be easily accessible. In the seven years I have been with EC and my composites experience before, I have only heard of balsa cores in this way generally for wet lay ups.

+x

 

John Hansen - 3/25/2019 9:37:24 PM

+x

 

Warren (Staff) - 3/25/2019 5:10:50 PM

The problem you have is not that many people are using a balsa core, especially in the more technical composite processes.  Sure it is more common in hand layup  on rc aircraft etc but not so common on carbon composite infusions.

Ignoring the balsa or assuming it is sealed and therefore has a negligible  resin uptake may be more sensible to getting a answer at  least to start with.

In this case you also need to assume the same basic layup with same fabric weights.

Like for like I would expect  the lightest layup to be pre-preg, followed by resin infusion, then wet lay vacuum bagging with, finally, wet lay up  as the heaviest.

This is mostly down to the fibre resin ratio achievable in each technique.  There is some overlap with all of them, eg a resin rich pre-preg part may be  slightly heavier than a  relatively dry (but still structurally sound) resin infused part.  A well vacuum bagged wet lay up can be almost as light as a fairly resin rich (for cosmetic reasons) infusion.   Some expert wet lay laminators can get their parts almost similar weight to resin infused - all down to skill and experience.  So there is cross-over but generally the Fibre resin ratio changes with each process.

Typically in a out of autoclave  pre-preg part you would be around 60:40 fibre resin ratio  - some fractionally dryer.
A resin infusion you always aim for 60:40  and most typical layups can get reasonably close to that , in practice I have seen a lot around 55:45 or a smidge closer to the ideal.
Wet lay  and wet lay vacuum bagging is typically starting on the heavy side at 50: 50 although with a bit of experience you can get it closer to 55:45  with careful vacuum bagging.  Complete newbies tend to be quite resin rich in their wet lay ups so could have an even higher resin ratio.

That is all fairly "broad brush" figures to get most people started. 

Without testing of your  specific core materials, you will struggle to find specific  data on the impact of the balsa core because, I just don't think the data exists or is not common enough to be easily accessible. In the seven years I have been with EC and my composites experience before, I have only heard of balsa cores in this way generally for wet lay ups.

Thank you Warren,
Your answer is both useful and perplexing. And oekmont's answer is equally useful. When we look at the reason that Balsa is used as a composite core for its properties of light weight and strength, I am puzzled that the most commonly used method of fabrication is potentially the heaviest. But neither of you have used the phrase "a lot heavier" as it relates to the difference in weight between resin infusion and prepreg. With so much balsa going into transportation and aerospace, I simply expected there to be data available on the topic. It is possible that the majority is skinned with fiberglass rather than CF.
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