On June 18, 2023, Titan, a deep ocean submersible
imploded during a voyage to the Titanic wreck site, killing all five occupants on board,
including Stockton Rush who was the founder & CEO of Oceangate, an American privately owned company
in Washington, that provides crewed submersibles for tourism, industry, research, and exploration.
We will explore what major factor could have led to such a catastrophic implosion in this video.
And it was not just the external pressure. I am Abhishek & welcome to Revolutionary Engineering.
Exploring the deep oceans poses several challenges due to the harsh and extreme conditions found at
great depths. But the biggest challenge is the pressure. As depth increases in the ocean, the
pressure exerted by the water column increases significantly. At a depth of 1000 meters,
the pressure reaches more than 100 times the atmospheric pressure & at 3800 meters where the
implosion of Titan occurred, it reaches over 370 times the atmospheric pressure. This is equivalent
to loading a square foot of surface with over 785 thousand pounds-force. Designing and constructing
vehicles or structures that can withstand these immense pressures without compromising integrity
is a complex engineering task. In 2018, a professional trade group warned that OceanGate's
experimental approach to the design of the Titan could lead to potentially "catastrophic" outcomes.
Although many experts could argue that the spherical structure for a submersible would be a
better choice as curvature of the sphere allows for an even distribution of the pressure load,
resulting in a more balanced stress distribution while in the case of Titan, its larger internal
free space combined with the elongated shape is susceptible to stress concentrations, accelerating
fatigue and delamination loads. But I have a point to make here. The elongated shape of a submersible
is generally designed to optimize its performance and functionality in deep waters. While the
specific design considerations and structural integrity of the Titan as far as its shape is
concerned would require detailed information, the elongated shape itself is not inherently
a limiting factor for withstanding loads in deep waters. In fact, many submersibles designed
for deep-sea exploration have elongated shapes to enhance stability and hydrodynamic efficiency.
The unconventional combinations of materials used in the Titan posed much higher safety risks as
the materials tend to weaken over the course of many pressurization cycles due to fatigue. Fatigue
failure is a failure that occurs when a material undergoes repeated loading and unloading cycles,
like the titan’s 5-inch thick hull experiencing repeated stress with changing hydrostatic pressure
over the course of a number of previous dives that it underwent. Fatigue failure can manifest as
the gradual growth of microcracks or delamination within the structure. These cracks can propagate
and eventually lead to catastrophic failure if not detected and addressed. But let's get back
to the basics. This disaster could have been avoided with the right engineering decisions.
OceanGate promoted the Titan’s carbon fiber construction — with titanium endcaps — as more
efficient to mobilize; being lighter in weight compared to other deep diving submersibles. It
also said the vessel was designed to dive 4000 meters (2.4 miles) “with a comfortable safety
margin. But carbon fiber composites can have multiple issues that we will see in a minute
especially when they are subjected to extreme pressures like the one that Titan underwent.
They can be stronger and lighter than steel, making a submersible naturally buoyant. But they
can also be prone to sudden failure under stress. non-destructive testing of Titan’s hull was
therefore absolutely necessary to ensure safety. Ultrasonic testing could help spot areas inside
the structure where the composites had cracks. But The company claimed their technology,
developed in-house, used acoustic sensors to listen for sounds of carbon fibers in case
of hull deteriorating to provide “early warning detection for the pilot with enough time to arrest
the descent and safely return to surface. This according to me as a mechanical engineer is the
biggest mistake as acoustic sensors would provide a real-time deterioration of the carbon fiber.
What if the orientation of carbon fiber in the structure itself is misaligned & goes undetected.
What I mean to say is Carbon fiber composites exhibit different properties when subjected to
compression compared to tension. Note how the fibers buckle under compression. This is due to
the anisotropic nature of carbon fibers meaning that the material exhibit different mechanical
or physical properties in different directions. The most important point to note here is the fiber
direction. When the load is applied parallel to the fibers, the composite exhibits higher strength
and stiffness making them highly effective in resisting forces that attempt to pull the
material apart. But In the transverse direction i.e. Perpendicular to the Fiber, the mechanical
properties are relatively lower compared to the fiber direction. This is because the load is
not effectively carried by the fibers in this direction. Instead, the matrix material primarily
supports the load which is generally less stiff and weaker than the carbon fibers. See how the
fibers are oriented in the hull of the submersible in this video from oceangate. The Carbon fiber
is being rolled along the circumference of the shell. As already pointed out, the load-bearing
capacity of the fiber is poor along the transverse direction, so any misalignment in fiber can easily
initiate deformation with the application of extreme pressure or fatigue. To better understand
this, let's take a very simple model of Titan. If we take only the carbon fiber shell, the
hydrostatic load on the shell can initiate deformation in the portion where fibers are weaker
or poorly aligned. But pressure alone could not have caused the implosion of the shell. This is
because the deformation of the shell from any side would cause tension on one side of the fiber
layers. This can be visualized from an exaggerated view in which a fiber experiences tension on the
bottom side when a force is applied from the top. And carbon fibers are very good at taking tensile
loads along the fiber direction. But the same deformation can also cause an increase in pressure
inside the shell itself that can lead to sudden increase in stress along the shell circumference.
This stress is both tensile and compressive in nature. Though carbon fiber can handle tensile
stress quite effectively, the radial stress that is compressive in nature is maximum on
the innermost layer & can buckle the fiber, thus aggressively accelerating the collapse of
the shell. All this in just a millisecond. This could be one of the most probable reasons of
titan collapse. Hence, Nondestructive testing was absolutely necessary that the company had
denied. OceanGate was also warned that a lack of third-party scrutiny of the vessel during
development could pose catastrophic safety problems. Apart from this, there is something
more that adds to uncertainty while dealing with carbon fiber. The Engineering design process
for any product usually starts with computational Animation Source: Finglow Consultants Ltd. modeling. But the anisotropic behavior of carbon
fiber composites adds complexity to the modeling process as the material properties need to
be defined and represented correctly in the model. On top of it, Carbon fiber composites
can have variations in fiber orientation, resin distribution, and manufacturing defects.
These variations can be challenging to capture accurately in computational models. It's not that
the management was unaware of these problems. David Lochridge, OceanGate’s former
director of marine operations, said in a 2018 lawsuit that the company’s testing
and certification was insufficient and would “subject passengers to potential extreme danger
in an experimental submersible.” In January 2020, Rush in an interview to GeekWire admitted that
the Titan’s hull “showed signs of cyclic fatigue. Because of this, the hull’s depth rating had been
reduced to 3,000 meters. But During 2020 and 2021, the Titan’s hull was either repaired or
rebuilt by two Washington state companies. The entire craft controlled using a video game
controller raises a serious question on the reliability of the craft. As any delays
or malfunctions in the communication or control signals between the controller and the
submersible's actuators or thrusters could lead to unintended movements or loss of control,
potentially compromising the safety of the mission. Deep ocean is still a hard-to-understand
environment and exploring such a territory is always associated with high risks. Wrong
engineering decisions can be sometimes life-threatening. Can carbon fiber be a choice
for deep-sea explorations? You may Comment in the section for any thoughts. I would appreciate
you subscribing to my channel as you would probably like some other videos like this one on
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