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Hole structure strengthens bone: horse

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horselegs_feature.jpg / Jurek Durcza.. / LicenseCC-by-nc - Attribution Non-commercial

A metacarpal bone of a horse avoids structural weakness caused by a hole via stress-dispersing microstructure.

BIOMIMICRY TAXONOMY
Summary

Zebras, horses and other equine species put substantial stress upon their central forefoot bones, particularly the third metacarpal, bones with remarkable strength despite having holes in them for blood vessels to pass through. The presence of a hole (or foramen) in a structural element offers the potential for it to act as a site of stress concentration and initiation of cracks, yet these foramina do not weaken the bone nor act as fracture initiation sites. Hence the foramen in the third metacarpal of equine species has been of interest to engineers to learn how to design openings in structures in a way that avoids cracking. The key features investigators have found that minimize cracking at these sites are: their location in regions predominantly experiencing compression, their elliptical rather than round shape (oriented parallel to the long axis of the bone and the lines of force), the ‘softening’ of the material discontinuity by increased compliance of the tissue surrounding the opening that shifts peak stresses away from the foramen edge, and a ring of increased stiffness reinforcing the foramen at some distance from it to absorb those stresses shifted inward from the compliant foramen edge. Many human-made structures, such as airplane wings, need to have holes in them to accommodate wires, fuel lines or hydraulic system elements and hence inspiration from the design of foramina in bones could have wide application.

Excerpt
"The third metacarpus bone in a horse's leg supports much of the force conveyed as the animal moves. On one side of the cucumber-size bone is a pea-size hole where blood vessels enter. As a rule, drilled holes weaken structures, causing them to break more easily than solid structures when pressure is applied, but nature has found a way of circumventing this rule…the (horse) bone was configured in such a way that it pushed the highest stresses away from the foramen into a region of higher strength…the bone's hole is also tougher than a typical drilled hole—more resistant to initial cracks growing to catastrophic lengths." (DeGaspari 2003:45)
About the inspiring organism
Horse
Equus caballa

Habitat(s): Grassland
Learn more at EOL.org
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

IUCN Red List Status: Unknown

Bioinspired products and application ideas

Application Ideas: Use for increasing strength of airplanes, boats, automobiles, other structures that have holes for wiring or fuel and hydraulic lines. (A quick rule of efficiency in the aerospace industry is that one pound of weight saved in a plane can save 10 pounds of fuel.)

Industrial Sector(s) interested in this strategy: Construction, manufacturing

Experts
Department of Mechanical Engineering, Union College
Andrew J. Rapoff at Union College. Also Raphael Haftka at Department of Mechanical and Aerospace Engineering, University of Florida, and Nils Götzen, now retired.
Union College
References
DeGaspari, J. Thoroughbred structures. Mechanical Engineering Magazine. March:
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Gotzen, Nils; Cross, Alan R.; Ifju, Peter G.; Rapoff, Andrew J. 2003. Understanding stress concentration about a nutrient foramen. Journal of Biomechanics. 36(10): 1511-1521.
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Comments

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Sherry
over 2 years ago
We had to remove the Autodesk Design Competition videos because the link disappeared from the Autodesk site.
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chanceliu
over 4 years ago
I could't view the animation
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