Point of impact: the effect of size and speed on puncture mechanics

Abstract

The use of high-speed puncture mechanics for prey capture has been documented across a wide range of organisms, including vertebrates, arthropods, molluscs and cnidarians. These examples span four phyla and seven orders of magnitude difference in size. The commonality of these puncture systems offers an opportunity to explore how organisms at different scales and with different materials, morphologies and kinematics perform the same basic function. However, there is currently no framework for combining kinematic performance with cutting mechanics in biological puncture systems. Our aim here is to establish this framework by examining the effects of size and velocity in a series of controlled ballistic puncture experiments. Arrows of identical shape but varying in mass and speed were shot into cubes of ballistic gelatine. Results from high-speed videography show that projectile velocity can alter how the target gel responds to cutting. Mixed models comparing kinematic variables and puncture patterns indicate that the kinetic energy of a projectile is a better predictor of penetration than either momentum or velocity. These results form a foundation for studying the effects of impact on biological puncture, opening the door for future work to explore the influence of morphology and material organization on high-speed cutting dynamics.

Getting out of an egg: Merging of tooth germs to create an egg tooth in the snake

“…The cutting dynamics would be interesting to test using controlled puncture experiments. 14 The development of the egg tooth in the snakes investigated here supports the congrescence theory (also known as integrated development) for the formation of large teeth. This theory proposes that large teeth could have evolved from the fusion of multiple tooth germs.…”

The comparative hydrodynamics of rapid rotation by predatory appendages

“…Unlike the hydrodynamics of locomotor systems that must balance propulsion with drag reduction, the diversification of feeding structures operate under a different constellation of factors, such as fracture resistance, effective prey capture morphology and the reduction of feeding costs (Anderson et al, 2016a;Anker et al, 2006;Full et al, 1989;Vermeij, 1987;Weaver et al, 2012). This study demonstrates that the shapes of fast, centimeter-scale predatory structures can diversify with relatively minimal costs within the steep constraints of size and kinematics in the generation of drag.…”

Making a point: shared mechanics underlying the diversity of biological puncture

“…However, tools traveling at high speeds will have a certain amount of kinetic energy (0.5mv 2 ; see Glossary) associated with them, determined by their size (mass) and speed. Previous experimental work has shown a strong correlation between kinetic energy and puncture depth (a proxy for the amount of fracture created) in ballistics gelatin (Anderson et al, 2016). These experimental results suggest that the kinetic energy of the tool in flight is directly connected to the energy used to create fracture surfaces in a target.…”

“…This rate-induced stiffening means the materials cannot dissipate energy through deformation as well, allowing more mechanical energy for fracture creation. This has been demonstrated in high-speed puncture tests on ballistics gelatin: the volume of material deformed is inversely proportional to the speed of the tool (Anderson et al, 2016). Imagine a viper fang impacting mammalian skin at different strain rates.…”