Experimental and numerical investigations of crack propagation in dragonfly wing veins

The vinous wings of insects are complex biological structures with remarkable mechanical behavior. The wings mainly consist of veins and membranes. The membranes of the wing are not mechanically tough. But, the whole wing structure reveals a significant resistance to crack propagation. In this paper, a combination of scanning electron microscopy technique, experimental tensile tests and numerical simulation is employed to investigate the effect of the veins on the “toughening mechanism” of the wings. The numerical simulation of crack propagation in the vein is based on the extended finite element method. Linear elastic material properties and linear traction-separation law are used to simulate the constitutive behavior of the vein materials. The microscopic images show that the veins have a tubular microstructure that consists of layers made of chitin and protein. The results from numerical simulations demonstrate that each vein layer effectively cope with the stresses due to external loading. But, the presence of protein plays an important role in arresting the crack growth. Comparison of the results reveals a very good agreement between numerical simulations and experimental data.