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A civil engineer has proposed that the fatal implosion of the Titan submersible last year may have been caused by “micro-buckling” in its carbon fibre hull.
Deep-sea entrepreneur Stockton Rush and his four paying crew members all perished last June when their submarine collapsed under pressure while on its way to explore the wreck of the RMS Titanic.
Experts had warned for years beforehand that the craft’s novel — and inexpensive — composite hull design might be vulnerable to tiny imperfections building up through repeated use.
Now researchers at the University of Houston and the University of Minnesota want to help prevent future disasters by statistically predicting the buckling strength of similar materials.
Although their study did not mention the Titan, its lead author Roberto Ballarini cited its destruction as a vivid example of what can go wrong.
“The material used for the Titan’s hull was a carbon fibre composite. It is well known that under compression loading the fibres in such composites are susceptible to micro-buckling,” said Mr Ballarini, who is a professor of civil engineering at Houston.
“If the Titan’s hull experienced such damage under the extreme compressive pressures during its dives, then its stiffness and strength would have significantly decreased. Together with the inevitable geometric imperfections introduced during its manufacturing, [that] may have contributed to its buckling-induced implosion.”
The study, which was published last month in the peer-reviewed academic journal Proceedings of the National Academy of Sciences (PNAS), attempted to use computer simulations to create a mathematical model predicting how and when small defects might lead to catastrophic failure.
Unlike most deep sea submarines, which are made of strong metal such as titanium, the Titan’s hull comprised a weaker carbon fibre cylinder capped at each end by two titanium domes.
Mr Rush, who founded and ran the submersible’s maker OceanGate, admitted that he had “broken some rules” by using such material but insisted he would be vindicated by reality, arguing that carbon fibre’s relative cheapness and inherent buoyancy would make deep sea exploration more commercially viable.
But OceanGate’s own former director of marine operations feared that small flaws in the hull could be widened into “large tears” by the repeated pressure changes, causing sudden failure.
Indeed, submarine designer John Ramsay later told the New Yorker that carbon fibre is inherently difficult to pressure test in a way that will indicate how close it is to failing ahead of time, meaning that each voyage would carry an unknown level of risk.
“Localised deformation and randomly shaped imperfections are salient features of buckling-type instabilities in thin-walled load-bearing structures,” the PNAS study said.
“However, it is generally agreed that their complex interactions in response to mechanical loading are not yet sufficiently understood, as evidenced by buckling-induced catastrophic failures which continue to today.”
OceanGate has ceased all operations and could not be reached for comment.
Source: independent.co.uk
