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Researcher Investigates Surface Erosion in Naval Vessel Components

Elastomeric Coating May Help Mitigate Cavitation Damage

Giant ship propeller
The nuclear-powered aircraft carrier USS Dwight D. Eisenhower (CVN-69) has a total of four massive bronze propellers, or screws, each weighing 30 metric tons.

By Edwin L. Aguirre

For full version of this story, please see Engineering Solutions Spring 2016 pdf. 
Cavitation poses a major challenge to Navy ships and submarines. The process occurs when water (or any other fluid) is moving very fast over a solid surface. When the pressure in the fluid drops, air and vapor bubbles are created.

“The bubbles eventually collapse and burst, and if this happens near the solid surface, the resulting intense shock wave can cause surface damage,” explains mechanical engineering Asst. Prof. Alireza V. Amirkhizi. “Eventually, this process may even create pits or holes in the fast-spinning metallic components of ships and subs such as propellers, turbines and pump impellers and gears.”

The Navy recently awarded Amirkhizi with a three-year grant totaling more than $300,000 to find the mechanisms of premature wear, damage or failure in materials exposed to cavitation conditions.

“Our goal is to find out whether compliant coatings, such as those used in everyday applications like truck-bed linings, may be used to combat this issue,” he says. “Specifically, my research team and I would like to find out what the mechanisms of damage in compliant coatings are compared to bare metal surfaces.”
Cavitating propeller
In this Navy water-tunnel experiment, the blades of a propeller produce cavitation bubbles.

According to Amirkhizi, elastomeric materials have surprising resilience and have been used in applications under extreme dynamic conditions. “This is the reason why we are approaching this potential nonconventional solution to a problem that previously was only approached by fabricating increasingly hard materials to resist erosion,” he notes.

Amirkhizi adds: “The equipment used by the Navy operates in far more challenging environments than commercial vessels, therefore their durability and reliability are of paramount importance. There hasn’t been a lot done in understanding elastomeric coatings under extreme conditions, and that makes our research quite exciting.”