Quake lessons from mussels

MICHAEL DALY
Last updated 13:09 24/07/2013

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Research which has finally solved the puzzle of how mussels cling to a surface as they are smashed by powerful waves could offer insights for building in earthquake-prone areas.

Unlike other species, such as barnacles, mussels dangle at a distance from the rock or ship or other surface they are connected to, attached by a collection of fine filaments called byssus threads. The threads are the beard removed before mussels are eaten.

By using the threads, mussels are able to drift out into the water where they can absorb nutrients, although they are then at risk from crashing waves.

Massachusetts Institute of Technology said the secret to the tiny natural bungee cords had been unravelled by MIT research scientist Zhao Qin and professor of civil and environmental engineering Markus Buehler. Their findings are published in the journal Nature Communications.

They found about 80 per cent of the length of the byssus threads was made of stiff material attached to the rock or other surface, with the remaining 20 per cent was a softer stretchy material connected to the mussel.

It turned out that in the dynamic, sloshing environment of waves and currents mussels could withstand impact forces nine times greater than the forces exerted by stretching in only one direction.

"Such an efficient, yet simple, architecture has clear application in inspiring artificial designs where energy absorption is required, with one possible example being for the design of structures in earthquake affected zones," MIT said.

Many researchers had studied mussel glue that anchored byssus threads to a surface, but the static strength of the glue, and of the thread itself, was not sufficient to withstand the impact of waves, Qin said.

It was only by measuring the system's performance in simulated wave conditions that he and Buehler could determine how mussels accomplished their amazing tenacity.

The researchers found the distribution of stiffness along the threads was key. The remarkable properties of mussel adhesion networks relied on a clever distribution of materials in a unique architecture.

The precise ratio of 80 per cent stiff material and 20 per cent softer and stretchier may be critical, enabling mussels to rapidly and effectively dissipate impact energy.

In their paper the researchers noted that dynamic loading - forces such as waves that move or change when acting on a structure - could be treacherous for engineered and natural systems because the force could easily become extremely large, leading to catastrophic failure.

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"For example, forces on a building's pillars during earthquakes or explosions reach several times that of its static weight," the paper said.

The structural and mechanical lessons gained by investigating the byssus network could provide important design principles.

They could be applied in making materials that could function under dynamic loading such as attachments to ships, submarines, wind turbines, and space technologies.

- Stuff

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