After the OceanGate Titan tragedy, a leading industry expert has hit back at the idea that carbon fiber composite is a problem.
In the wake of the OceanGate Titan disaster, in which the founder of the OceanGate ocean exploration company and four passengers died when a small submersible failed en route to the Titanic site, much speculation has turned to the use of carbon fiber composite in the submersible’s design.
Now a boatbuilding industry veteran has hit back with a defense of the material.
In the days since the tragedy, Phil Friedman has seen assertions that carbon fiber composite lacks the strength of steel or titanium, won’t work for pressure vessels where the load is outside the structure, can delaminate under pressure and can fail suddenly, unlike ductile metals which first visibly distort.
In his newsletter, the Port Royal Group managing director hit back against those claims. When it comes to strength, you have to consider a number of factors. Friedman used the example of steel vs aluminum.
“Steel is a lot stronger per square inch of cross-sectional area than aluminum, but it is also a lot heavier per cubic foot — 490 lbs per cu foot for steel vs 169 lbs for aluminum. Thus, aluminum weighs about one third what steel does per unit volume. On average, steel is about twice as strong as aluminum per unit of cross-sectional area. Consequently, the rule of thumb is that, for a given load, you can build an aluminum structure at about two-thirds the weight of a steel one, all other factors held constant.
“Carbon fiber composite carries about five times the load as steel per unit weight, when that load is properly engineered to align with the majority of the reinforcing fibers. (And provided, of course, that the polymer matrix is an appropriate epoxy plastic.) So, a carbon fiber compression hull skin in a deep diving submersible could be five times stronger for the same weight as a steel one. Moreover, it could also be five times thicker — which is, in itself, beneficial because structural rigidity is significantly enhanced by thickness.”
Regarding carbon fiber composites in compression rather than tension, he writes: “CF composite is somewhat less strong in compression than CF composite in tension, but it is still stronger than steel per unit weight whether in tension or compression.” Regarding a tendency to delaminate, he added that “I personally doubt that the CF reinforcing goes entirely unloaded when the composite is in compression, and I for one would want to see systematic testing to prove that claim before giving that theory any credence.”
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Tagged carbon fiber composite, OceanGate, Titan
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