Findings: A hole lot of horse power

December 6, 2002

A horse's leg bone is providing the inspiration for a new generation of synthetic materials.

Analysis of the microstructure of the animal's third metacarpus has revealed a way to strengthen weak spots, which could prove useful in the construction of aircraft and space probes.

This cucumber-sized bone supports much of the force exerted when the horse is moving, yet it contains a pea-sized hole for blood vessels.

Holes weaken structures, but something in the structure of the third metacarpus makes it remarkably resistant to fracturing - when horses break this bone it is usually in some other area.

Engineers from the University of Florida in the US analysed the bone around the hole, called the foramen, using microscopy and microradiography.

From this analysis, they developed a computer model that mimicked the metacarpus's behaviour under stress.

They found that the structural units of the bone served to route stress around the hole and away into regions of greater strength.

Andrew Rapoff, an assistant professor or aerospace and mechanical engineering, said: "Holes are a classic source of failure in engineered structures, but nature has found a way around that in this bone."

Holes appear in many structures, such as for wiring, fuel and hydraulic lines in aircraft. The usual way to compensate this inherent weakness is to reinforce the material surrounding the holes but this adds weight.

The engineers have been able to copy the horse bone using several grades of polyurethane foam aligned around a hole to mimic the structural units.

In laboratory trials, their metacarpus-inspired test plates took twice the weight before they broke than similarly perforated sheets without the foam.

The findings will be published in the Journal of Biomechanics .

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