E34 Impact resistance

Topic

An insect's resistance to impact is extraordinary given its small body size; consequently, an ant can fall from a considerable height and survive the fall, while its trap-jaw—another structural feature—strikes at a remarkably high speed.

Hertzian impact theory predicts both the peak force and the duration of the contact—modeled here as a dynamic impact between two elastic bodies.

The insect's coefficient of restitution quantifies the kinetic energy conserved during the impact; energy dissipation within the cuticle and the body itself attenuates the impact force. If the cuticle dissipates a larger proportion of the kinetic energy, the resulting impact force on the insect is further reduced.

The cuticle's fracture toughness determines the maximum defect size it can tolerate without catastrophic crack propagation.

The sclerotized cuticle possesses a crack-arresting structure similar to that found in the nacre of a comparable mollusk. Consequently, the extraordinary impact resistance demonstrated by this model—relative to the insect's body size—allows the mantis shrimp to harness the final cavitation wave generated upon impact with the water (specifically, a distinct shock-wave dynamic) to produce a final pressure capable of shattering a similarly hard shell. The generation of an even more intense cavitation wave results in a correspondingly higher final pressure exerted against the hard shell, thereby pushing the model's impact resistance even closer to its own extraordinary limit.

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