Carbon Fibre also is known to tear suddenly and expectedly.
There are several important reasons why steel displaced iron as the preferred material for structural framing in buildings and bridges long ago. One big one is that steel deforms as it fails, while iron tends to fracture suddenly with little or no warning.
But carbon fiber is inspiring to 20 something engineers.
Those "uninspiring" 50 year old White men would have told him "No. In fact HELL NO!!!"
Dittos. I was just a dirty-fingernail mechanical penguineer, working mostly in machine tools and then automotive process control, but even at that I was incredulous that anybody would use CF for a submarine hull. Still trying to imagine how they laid it up. No aerospace tape-layer I ever saw would do it.
Link is no bueno.
Carbon fiber composites have huge positives and and some really bad negatives. Hulls for deep seas submersibles cannot take advantage of the positives of composite construction and are uniquely impacted by the negatives.
Furthermore, it looks like the composite section of the vessel used a technique known as wet winding which is totally inappropriate for this application due to lack of control of the process and susceptibility to defects that lead to critical safety problems.
And nobody in their right mind uses a cylindrical vessel for deep sea work, everyone uses spherical vessels .
Carbon fiber is not the issue, it’s the application in use.
Carbon fiber is wonderful stuff, I machine it all the time. What I’m understanding about it from the engineers I work with is that it’s great stuff for elongation pressures, but the epoxy would want to start failing in a compressive state. The fibers are meant to hold up under expansion just fine, they are tough as hell and won’t stretch at all, it’s why they are so good for high pressure tanks from the inside. These forces are exactly opposite of that, the pressure wants to push the fibers shorter and then the epoxy comes in to hold the shell rigid. I would love to see the FEA analysis of the sub, especially around the Plexiglas portal area. Wouldn’t it be interesting if Ansys or Nastran showed it failing at only 8% or so safety factor instead of something much higher like what OSHA would demand.
“He hired young engineers, who were cheaper, and who would not tell him their was something wrong with the design.”
He fired the old engineer who detailed the many reasons why the submersible was unsafe.
The young engineers got the message—shut up and keep getting your paycheck.
Yup.
People use a material irresponsibly....then it’s the materials’ fault.
Just like firearms.
Idiocracy proven right, AGAIN.
1. It is impossible to use non-destructive testing (NDT) on composite materials and get useful results.
2. The carbon fiber was wound onto the mandrel without using a criss-cross pattern which results in a weaker pressure vessel.
3. Carbon fiber is a very brittle, not ductile, material. Look at the mess on the track after any Formula 1 crash.
3. You have the differential thermal expansion problems you mentioned as well as differential strain caused by pressure.
4. Carbon fiber suffers its own type of cyclic fatigue and this submersible had been through quite a few cycles.
5. The manufacturer of the acrylic viewport would not certify it for 4,000 meters. It was apparently certified for only 1,500 meters depth.
Other than those few minor things, it was a safe vehicle.
I had not read that Rush bought old carbon fiber at a discount. Is there really an age limit on CF for aircraft usage?
working link:
I read someplace yesterday that the sub only had about 20 hours of oxygen not 90
seems like something an over-egoed business guy would do. I am always disgusted that some people think they know better than a qualified, experienced engineer...especially when death is on the line.
Here’s an excerpt from a CBS interview with Rush, the OceanGate CEO and Titan pilot:
Rush: . . . We have eight acoustic sensors in there, and they’re listening for this. So when we get to 1,000 meters, if all of a sudden we hear this thing crackling, it’s, like, “Wait, did somebody run a forklift into it? You know, has it had cyclic fatigue? Is there something wrong?”
And you get a huge amount of warning. We’ve destroyed several structures [in testing], and you get a lotta warning. I mean, 1,500 meters of warning.
It’ll start, you’ll go, “Oh, this isn’t happy.” (LAUGH) And then you’ll keep doin’ it, and then it explodes or implodes. We do it at the University of Washington. It shakes the whole building when you destroy the thing.
So that’s our backup for the hull. And we’re the only people I know that use continuous monitoring of the hull.
POGUE: So if you heard the carbon fiber creaking—
RUSH: If I heard the carbon fiber go pop, pop, pop, then the gauge says, “You’re getting a whole bunch of events.”
POGUE: Could you get three hours back to the surface in time?
RUSH: Yes. Yes, ‘cause what happens is once you stop going down, the pressure, now it’s easier. You just have to stop your descent. And so that’s what we did a lotta testing on. You know, what kinda warning do you get?
And as I said, the warning is about 1,500 meters. It’s a huge amount of pressure from the point where we’d say, “Oh, the hull’s not happy” to when it implodes. And so you got a lotta time to drop your weights, to go back to the surface, and then say, “Okay, let’s find out what’s wrong.”
I read speculation somewhere that the submersible was on the way up when disaster struck. I wonder if the ship monitoring it knew of problems and of a possible return or if it detected the noise of the implosion.
Kraft paper, one of Niagara Daredevil’s experimental materials, comes under scrutiny.
I am not an engineer. However, 3 countries have had deep sea submusibles for 30-60 years, and their may be private ones. Why wouldn’t you copy what was already working rather than innovate? I guess a cylinder was better for carrying more paying passengers than a sphere.
Don’t forget the recycled ballast , they had move to one side to get it to drop off and then I suppose the sub would lurch back the other way and drop the other side’s ballast ,scary
The strength of carbon fiber layup is vastly overrated. S-glass is stronger in almost every way. Other important aspects include monolithic layup, multiple layers, and vacuum bagging (fabric-to-resin ratio).