Study on bio-inspired feet based on the cushioning and shock absorption characteristics of the ostrich foot.

Dianlei Han,Rui Zhang,Guolong Yu,Lei Jiang,Jianqiao Li,Dong Li,John Leicester Williams

doi:10.1371/journal.pone.0236324

Abstract

As the main actuator of high-speed running, the ostrich feet are highly capable of cushioning and shock absorption. In this study, based on the elastic modulus scales and assembly order of the 3rd toe soft tissues and the functions of the metatarsophalangeal (MTP) joint, we designed fourteen bio-inspired feet. The impact process on loose sand was simulated on the finite element software Abaqus. Also the stress distributions and deformations of each component of the bio-inspired feet were clarified. With the peak acceleration as the index, the cushioning performances of the bio-inspired feet were compared on both loose sand and solid ground through height-variable impact tests. The 15-15-15 HA (hardness unit) bio-inspired foot showed lower peak acceleration and thereby better cushioning performance, but larger deformation, less-uniform stress distribution and thereby lower stability than the 15-35-55 HA bio-inspired foot. In fact, the silicon rubbers with different hardness degrees (which simulate the elasticity modulus scales of the digital cushions, fascia and skin) and the spring mechanism (which simulates the functions of the MTP joint) work as an “integrated system” of cushioning and shock absorption.

Highlights

When the feet of large-weight running animals contact with the ground, the hindlimbs need to bear the ground impact
In this study, inspired by the assembly order of ostrich plantar soft tissues, we aimed to study how to assemble the plantar soft materials to improve the cushioning and shock absorption effects on loose sand
The elasticity modulus scales of the skin, fascia and digital cushions were simulated from silicon rubbers with different hardness degrees and assembled into bio-inspired feet according to the assembly order of soft tissues

Summary

Introduction

When the feet of large-weight running animals contact with the ground, the hindlimbs need to bear the ground impact. To prevent the hindlimb bones and tissues from damage or destruction, these animals should reduce ground stress waves as much as possible [1]. After long-term natural selection and evolution, excellent running animals have inevitably developed efficient cushioning and shock absorption systems to avoid injury during locomotion. This phenomenon can be illustrated by many cases. The large subcutaneous cushions in the feet of African elephants (Loxodonta africana) are pivotal in distributing forces during weight-bearing and in storing or absorbing mechanical forces [2,3,4,5,6].

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