Titan submersible implosion-an afterthought

The recent accident involving the implosion of the Titan submersible was really unfortunate, killing all onboard. There are various media news subsequent to this indicating possible design lapses and inspection mechanism.

?Design was cylinder-shaped cabin made of a carbon-fiber which is unlike the sphere-shaped cabins made of titanium normally used by most submersibles.

The sphere is “the perfect shape,” because water pressure is exerted equally on all areas, said Chris Roman, a professor at the University of Rhode Island’s Graduate School of Oceanography.

Under its usage conditon the vessel is subjected to high load and pressure cycles due to hydrostatic conditions, thus causing possibility of tear, delamination and fatigue .

Furthermore, the Titan’s hull had been subjected to repeated stress over the course of about two dozen previous dives, as per Graham-Jones .

Each trip would put tiny cracks in the structure. “This might be small and undetectable to start but would soon become critical and produce rapid and uncontrollable growth,” he said.

The construction of vessel was Carbon fiber with end cap in Titanium . Carbon composites have limited life when subject to excessive loads or poor design which leads to stress concentrations, Graham-Jones said.

“Composites are extremely tough and are extremely long-lasting. But we do have issues with composites and the fact that composites fail in slightly different ways than other materials,” he said.

Finally, there was no certification and testing for the design and condition of the submersible. Ideally at the material stage for the composite and nondestructve testing using ultrasonic testing should have been performed to assess the health of the submersible before this mission.

This further proves a point that all engineering structures, including automotive, appliances, engineering components like pumps, valves involving both metallic, non Metallic and composite construction shall be properly verified and validated for the design aspect which is primarily based on benchmarking and QFD.

Also the material and manufacturing processes shall be properly studied controlled and tested for any lacuna.

Any design is required to be properly validated for the specific usage condition including physical validation and nondestructive testing specially by third party agencies till all the possible gaps are taken care in the material/manufacturing process/any design aspect.

Composites are widely used for lightweight design which is a trend in present designs. However, due to the failure mode of composites, more work needs to be done for self-healing polymers and composites.

Jasper Graham-Jones, an associate professor of mechanical and marine engineering at the University of Plymouth in the United Kingdom.

QFD :Quality function deployment