It definitely gets 'fuzzy' once all factors are being considered. I recall a study done by a carbon fiber mast builder that compared a vacuum+oven mast to an autoclaved version of identical construction. Shockingly, the autoclaved version underperformed. Their engineers came to understand that the additional compaction had reduced wall thickness enough that the tube (mast) became weaker from a purely geometrical standpoint. That scenario altered the way I think about composites --sometimes you don't really want what you think you want, i.e. fiber ratios, compaction, etc.
You raise an interesting point, Chuck -- one that we had to consider when building carbon fiber masts at Tartan yachts. But the issues involved are not fuzzy at all. In the case of a stayed mast, you are dealing with two distinct and different failure modes: 1) Euler long, slender column overall buckling failure, and 2) catastrophic wall failure due to local buckling. The first of these happens when the load vectors created by the rigging cause the long, slender column of the mast to deflect overall in an "attempt" to squirm out from under the load. The result of this is that the rigging goes slack (and thereby relieves the load) and the performance of the sails reduces drastically. In general, Euler overall buckling is not a fatal failure -- unless the mast also experiences local wall buckling which will lead to a complete structural failure. Resistance to Euler long-column buckling is proportional to the moment of inertia of the mast section, which weight for weight, you can increase by increasing overall cross-section dimension. The result is a very stiff mast at minimum weight. Unfortunately, doing that generally reduces wall thickness (if you hold weight constant), and that reduces resistance to local wall buckling. The design issue is to find the sweet spot between optimized overall mast section dimensions and minimum wall thickness to resist local buckling. But its the same problem with aluminum and wood masts as it is with carbon fiber. Thanks for reading and commenting. Cheers!
Talk about low odds, discussing carbon mast construction with someone who's built them! IIRC the company (I forget the name) had a more or less similar analysis of the failure modes. To my mind, the fuzzy part was that they were faced with having to add material in order to restore lost performance from increased compaction. The tone of the paper was along the lines of an autoclaved mast not being stronger. Ceteris paribus, from a strictly CFRP BOM, that was probably true in their case. That doesn't even touch on how much cost would be added by autoclaving lol. Cheers!
Again, Chuck, you make several good points. One of which is that structural rigidity is just as much a function of shape (and effectively, thickness) as of material strength. Which is why in many composite structures we replace the heavier, stronger materials at the center of the structure with foam cores and put the majority of the strong material out near the surface of the structure. It is also why over compacting a laminate (carbon fiber or otherwise) might work out to be counter-productive -- as you point out. Cheers, bud. Good to talk with you.
It definitely gets 'fuzzy' once all factors are being considered. I recall a study done by a carbon fiber mast builder that compared a vacuum+oven mast to an autoclaved version of identical construction. Shockingly, the autoclaved version underperformed. Their engineers came to understand that the additional compaction had reduced wall thickness enough that the tube (mast) became weaker from a purely geometrical standpoint. That scenario altered the way I think about composites --sometimes you don't really want what you think you want, i.e. fiber ratios, compaction, etc.
You raise an interesting point, Chuck -- one that we had to consider when building carbon fiber masts at Tartan yachts. But the issues involved are not fuzzy at all. In the case of a stayed mast, you are dealing with two distinct and different failure modes: 1) Euler long, slender column overall buckling failure, and 2) catastrophic wall failure due to local buckling. The first of these happens when the load vectors created by the rigging cause the long, slender column of the mast to deflect overall in an "attempt" to squirm out from under the load. The result of this is that the rigging goes slack (and thereby relieves the load) and the performance of the sails reduces drastically. In general, Euler overall buckling is not a fatal failure -- unless the mast also experiences local wall buckling which will lead to a complete structural failure. Resistance to Euler long-column buckling is proportional to the moment of inertia of the mast section, which weight for weight, you can increase by increasing overall cross-section dimension. The result is a very stiff mast at minimum weight. Unfortunately, doing that generally reduces wall thickness (if you hold weight constant), and that reduces resistance to local wall buckling. The design issue is to find the sweet spot between optimized overall mast section dimensions and minimum wall thickness to resist local buckling. But its the same problem with aluminum and wood masts as it is with carbon fiber. Thanks for reading and commenting. Cheers!
Talk about low odds, discussing carbon mast construction with someone who's built them! IIRC the company (I forget the name) had a more or less similar analysis of the failure modes. To my mind, the fuzzy part was that they were faced with having to add material in order to restore lost performance from increased compaction. The tone of the paper was along the lines of an autoclaved mast not being stronger. Ceteris paribus, from a strictly CFRP BOM, that was probably true in their case. That doesn't even touch on how much cost would be added by autoclaving lol. Cheers!
Again, Chuck, you make several good points. One of which is that structural rigidity is just as much a function of shape (and effectively, thickness) as of material strength. Which is why in many composite structures we replace the heavier, stronger materials at the center of the structure with foam cores and put the majority of the strong material out near the surface of the structure. It is also why over compacting a laminate (carbon fiber or otherwise) might work out to be counter-productive -- as you point out. Cheers, bud. Good to talk with you.
Good stuff, Phil--I'm enjoying your many insights and talking shop. Cheers-