Meeting Abstract
Elastic energy exchange is thought to offset the high power requirements of insect flight. For significant elastic return, a structure must be stiff to store energy and resilient (energy return/energy in) to minimize dissipation. Structures that may serve this role are the viscoelastic musculature and thoracic exoskeleton, which contains highly resilient proteins. We have shown that the exoskeleton of the hawkmoth Manduca sexta can return up to 20% of inertial power requirements with a 75% resilience over a wide frequency range. However, thoracic material properties, shape, and musculature may all contribute to this storage and return. Using a custom material testing device, we measured the force required to drive sinusoidal displacements of the thorax in four experimental conditions: 1) longitudinal cuts disrupting the transverse arch, 2) cuts through the wing joints to isolate the curved scutum, 3) isolated wing joints with scutum removed, and 4) intact thorax with passive muscles. We examined a frequency range from 0.1 to 90 Hz to span the hawkmoth’s wingbeat frequency of 25 Hz. Each of the three cut conditions led to decreased stiffness (27 ± 7%, 49 ± 12%, 67 ± 21%). While resilience also decreased (9 ± 0.4%, 18 ± 1%, 20 ± 3%), the response was not proportional to the stiffness change, indicating an increased structural damping coefficient (37 ± 4%, 77 ± 8%, 66 ± 24%). The presence of muscle had no significant effects. Videos of thorax deformation show non-uniform strain, indicating that shape alters localized strain. Changes in local strain coupled with material heterogeneities may affect macroscopic behavior. Overall, material alone cannot predict mechanical properties. Shape matters for thoracic energy exchange.
