Numerical investigation of insect wing fracture behaviour.

The wings of insects are extremely light-weight biological composites with exceptional biomechanical properties. In the recent years, numerical simulations have become a very powerful tool to answer experimentally inaccessible questions on the biomechanics of insect flight. However, many of the presented models require a sophisticated balance of biomechanical material parameters, many of which are not yet available. In this article we show the first numerical simulations of crack propagation in insect wings. We have used a combination of the maximum-principal stress theory, the traction separation law and basic biomechanical properties of cuticle to develop simple yet accurate finite element (FE) models of locust wings. The numerical results of simulated tensile tests on wing samples are in very good qualitative, and interestingly, also in excellent quantitative agreement with previously obtained experimental data. Our study further supports the idea that the cross-veins in insect wings act as barriers against crack propagation and consequently play a dominant role in toughening the whole wing structure. The use of numerical simulations also allowed us to combine experimental data with previously inaccessible data, such as the distribution of the first principal stress through the wing membrane and the veins. A closer look at the stress-distribution within the wings might help to better understand fracture-toughening mechanisms and also to design more durable biomimetic micro-air vehicles.