Relaxation and dynamic experiments were carried out on the hind leg of Blaberus discoidalis to aid in the selection of a material behavior model and to quantify measures of roach leg response. During testing, the coxa of the ablated metathoracic limb (hind limb) of the cockroach was epoxied to 3/8" acrylic such that the coxa-femur and femur-tibia joints were free to rotate. Cyanoacrylate was used to attach one end of a stainless steel pin to the distal tip of the tibia; dental impression compound was used to adhere the other end of the pin to the arm of a servo-motor system. The leg was then displaced with the Aurora system, which is based upon a high performance rotary moving coil motor supported by precision ball bearings. The results are that the total error in the force-displacement measurements to be less than four percent that of a viscoelastic solid.
The results indicate that a cockroach leg excited in a direction orthogonal to the joint direction behaves similarly to a viscoelastic material. The exponential nature of the force relaxation curves suggests viscoelasticity. The hysteretic nature of the force-displacement curves indicates that there is energy loss due to the internal friction, which is a common characteristic for viscoelastic materials. The cockroach leg is subject to a combination of bending and torsion in the experiment. The overall effect can be modeled as a torsion spring with a moment arm. Additional assumptions for the model include: (1) the axis of rotation for the leg is constant during torsion and (2) the joint material can be approximated using a lumped-parameter element with uniformly distributed linear viscoelastic p
Contact: Donna Krupa
American Physiological Society