The sort of catastrophic implosion that occurred on OceanGate’s Titan submersible last year, when five people died while diving to see the 3.8km deep wreck of the Titanic, could be avoided in future because of a study of the effects of “geometric imperfections” at the University of Houston.
Researchers led by Prof Roberto Ballarini, chair of the Texas university’s civil & environmental engineering department, say that thin-walled structures such as Titan are susceptible to “buckling-induced collapse” as a result of random flaws that occur during the manufacture of the shell.
The submersible industry had enjoyed a good safety record until the Titan incident. The researchers were not studying the carbon-fibre Titan specifically, but cite it as an example of a slender craft constructed to withstand high pressures through the strength and stiffness of materials used in a spherical or cylindrical shell.
The microscopic geometric imperfections inherent in manufacture can cause “micro-buckling” under much smaller forces than if the shell was perfectly shaped, say the researchers.
This buckling starts where these imperfections are most severe but, because they are randomly distributed, predicting their negative effects had proved impossible until now.
Modelling imperfections
Ballarini claims that his team have been able to derive 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”. The simulations “spit out” the average buckling resistance of the structures.
The professor also suggests that the Titan’s integrity “might have been compromised by the damage to the material used for its hull that accumulated during the many trips it took prior to collapse.
“It is well known that, under compression-loading, the fibres in such composites are susceptible to micro-buckling and that they may delaminate from the matrix that surrounds them.
“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 model for the statistical distribution of buckling resistance produced by Ballarini, working with doctoral student Zheren Baizhikova and University of Minnesota Prof Jia-Liang Le, is said to offer promise for creating structurally reliable lightweight and sustainable structures such as submersibles without unnecessary over-design in future.
The study has just been published in Proceedings of the National Academy of Sciences.
Also read: Search continues for missing Titanic sub, Titan sub debris recovered from seabed
