Wing Veins Improve Fracture Toughness

photograph of brown and white flying locust

Biological Strategy

Desert locust

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Manage Mechanical Wear

A living system is subject to mechanical wear when two parts rub against each other or when the living system comes in contact with abrasive components in its environment, such as sand or coral. Some abrasive components are a constant force, such as finger joints moving, while others occur infrequently, such as a sand storm moving across a desert. Living systems protect from mechanical wear using strategies appropriate to the level and frequency of the source, such as having abrasion-resistant surfaces, replaceable parts, or lubricants. For example, human joints like shoulders and knees move against each other all day, every day. To protect from mechanical wear, a lubricant reduces friction between the cartilage and the joint.

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Prevent Fracture/Rupture

High force impact or stress can cause materials that comprise living systems to separate into two or more pieces (called fracturing) or to break or burst suddenly (called rupturing). For example, a scallop prevents structural failure from fracture because its shell is comprised of two materials of varying stiffness. When a crack moves from the scallop’s stiff material to the less stiff one, the latter reduces the force at the tip of the crack, thereby stopping it from spreading farther.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Veins on wings of migratory locusts improve fracture toughness by acting as barriers to crack propagation.

Image: Yasunori Koide / Wikipedia Commons / CC BY SA - Creative Commons Attribution + ShareAlike

Locust, showing exposed hind wings. Note: locust pictured is a different species than locust studied in the cited research.

Flying insects’ wings must hold up to millions of cycles of mechanical forces, deformations, and minor impacts, while also being extremely lightweight in order to optimize flight performance. The hind wing of the migratory locust S. [Schistocerca] gregaria is composed of thin and fragile membrane cells supported by a lattice structure of veins which increase the wing’s toughness by 50% and act to distribute stresses during flight and prevent crack propagation. The morphological spacing of most wing veins matches the “‘critical crack length’ of the membrane, which is determined by the material’s fracture toughness and the stress applied. At a given stress, any crack smaller than the critical length would have no structural effect. As a consequence, the largest possible cell size that prevents cracks from self propagating corresponds to this critical crack length. If a crack is contained within this cell, it cannot reach a critical length to self propagate through the rest of the wing. Any cell bigger than this critical crack length would allow the initial crack to start growing. However, any cell smaller than this critical crack length would be a ‘waste’ of vein material.” (Dirks and Taylor 2012: 7)

Image: Jan-Henning Dirks / PLOS One / CC BY - Creative Commons Attribution alone

(a) Schematic illustration of the three wing zones R, B and C used for the experiments (adapted from [8]). (b) Longitudinal veins (LV) with branching cross veins (CV). Towards the edge of the hind wing the two types of veins show a different morphological structure. Whilst the longitudinal veins mostly show a circular to elliptical cross section, the cross veins show an annulated pattern. (c) Cross section through the wing membrane and a cross-vein. Note that the cutting edge of the wing membrane slightly “crumpled” during the desiccation. (d) Close-up of a cross-vein, showing the compartment-like annulated structure.

Last Updated September 14, 2016

References

Journal article

Veins Improve Fracture Toughness of Insect Wings

PLoS ONE | 22/08/2012 | Jan-Henning Dirks, David Taylor |

Markus J. Buehler

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Reference

Web page

Transparent, thin and tough: Why don't insect wings break?

ScienceDaily | 22/08/2012 | Trinity College Dublin

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