Friday, May 24, 2013

Seahorse's tail strength and conjugate shearing

Earlier I wrote a blog entry here on Nature’s masons.  I tried to describe how nature offers inspired design solutions from different animals which use properties of masonry to their advantage, including: foraminifera, radiolaria, coral, sea anemones, turtles, tortoises and more.   Today I want to attempt to describe a masonry feature used by another animal, the seahorse.

Seahorse’s tails have a bony structure which withstands extreme pressures without breaking.  The bones of the tail form a roughly square limb in cross section.  There are sets of four corner bones to this tail structure which run its length.  These four bones are triangular, and are disposed to conjugate shearing.

I have discussed conjugate shearing and how masonry structures can benefit from conjugate shearing as a means to relieve stress(applied force) through strain (movement).   This is just how a seahorse’s tail reacts to any threatening stress: it deforms via conjugate shearing instead of breaking.  When the stress is relieved the triangular bones return to their original position, tail intact.

A paper recently published in Acta Biomaterialia (Highly deformable bones: unusual deformation mechanisms of seahorse armor   Michael M. Porter et al, published Fe. 26, 2013) describes the elegant design of seahorse tails, including the bony structure and how it allows for conjugate shearing, making the tail very strong, robust and tough.

The design of a seahorse tail has inspired human designers to employ the same concept in robotic armor design, as discussed in several recent articles.  Nature is always an inspiration for good design.