Titan submarine: “Carbon fiber is just as strong as titanium”

Critics abounded about the type of carbon fiber construction of the Titan submarine, which imploded near the Titanic. Did you understand them?

Florian Madec, FMC composites in Brest*: It’s wrong to say that composites aren’t suited to great depths. We have been releasing since 2005, in series, carbon fiber parts capable of withstanding pressure at depths of more than 6,000 m. For nearly 20 years, none of our composite parts have been destroyed by pressure. Some elements remained submerged for years at great depths and came up intact.

Carbon is just as strong as titanium, provided you put the right thickness and the fiber in the right direction to withstand the pressure. The weight gain is considerable. This is what motivated the construction of this first submarine of its kind.

The Titan was not a certified submersible. How do you certify your parts?

There is no external approval. We practice self-certification using various resistance tests that we carry out at the production site. Using our hyperbaric chamber, we apply up to 900 bars of pressure to simulate immersion up to 9,000 m, with a safety factor of 1.5 for a contractual immersion of 6,000 m. We sometimes push to the breaking point, in addition to fiber cycling and fatigue tests.

How to explain that no organization certifies these elements?

Due to lack of market. There are too few gears to go to the great depths. No one agrees to approve this kind of prototype. Where to find the points of comparison when there is only one model? Where to find the sufficiently voluminous boxes?

Did the Titan experience material fatigue during its dives?

He didn’t have enough immersion hours for that. The problem probably came from elsewhere. A handling shock that could have weakened a place? A fixing point that has let go? A porthole too big? The builder assures that it used sensors to regularly check the structure and a live monitoring system.

What happened to the bodies of the five victims after the implosion?

It’s hard to imagine. When we go so far as to break a part in our hyperbaric chamber, I can assure you that the whole workshop is aware. It makes an impressive noise and only fragments are found inside. At this depth, only water should remain.

Would you board a carbon fiber submarine?

Yes, if it was designed here and I carried out the pressure resistance tests of the materials used.

*FMC Composite, in Brest, supplies parts for oceanography, military and offshore activities, and collaborates with Ifremer.