Scientists have figured out what might have caused the Titan submersible to collapse under pressure last summer.
In a story that took the world by storm, OceanGate's Titan submersible went missing with five people on board on June 18 during an expedition to explore the wreck of the Titanic.
Initially, the submersible was feared to have lost power or been otherwise unable to return to the surface, triggering mass search-and-rescue efforts over the subsequent days, but it turned out that the vessel had imploded mere hours into the trip, instantly killing everyone on board.
In a new paper in the journal Proceedings of the National Academy of Sciences (PNAS), researchers from the University of Houston reveal what might have gone wrong with the structure of the submersible to result in such a catastrophic failure.
Thin-walled structures like that of the Titan—or a car, or plane—can withstand large amounts of pressure, but are vulnerable to collapse due to their thin walls buckling. A perfectly shaped cylinder should theoretically be quite hardy, but any imperfections in manufacture can mean that the structure buckles at smaller forces than expected.
Using computer simulations and extremely complicated math, the researchers have predicted the average buckling strength of a shell with imperfections.
"We derived equations that allow us to predict the resistance to buckling of structures in terms of the parameters that are involved including the shapes and distribution of their imperfections," Roberto Ballarini, a professor of civil and environmental engineering at the University of Houston, said in a statement. "Given the parameters that describe the imperfections, the equations we constructed using the results of the simulations 'spit out' the average buckling resistance of the structures."
"One must not forget that a structure's resistance to buckling failure is also affected by the strength and stiffness of the material from which it is made," Ballarini said.
These simulations may reveal why the Titan submersible—made of carbon fiber and titanium—buckled when and where it did.
"Its integrity may have been compromised by the damage to the material used for its hull that accumulated during the many trips it took prior to collapse. The material used for the Titan's hull was a carbon fiber composite. It is well known that under compression loading the fibers in such composites are susceptible to micro-buckling and that they may delaminate from the matrix that surrounds them," Ballarini said.
"If the Titan's hull experienced such damage under the extreme compressive pressures it experienced during its dives, then its stiffness and strength would have significantly decreased, and together with the inevitable geometric imperfections introduced during its manufacturing, may have contributed to its buckling-induced implosion."
The buckling may have begun at the point of most severe imperfections, but since geometric imperfections are often randomly distributed around a shell like the Titan, the location of initial buckling may also be random.
"This randomness has profound implications for the statistics of the critical buckling pressure of the shell," said Ballarini.
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