Mechanisms of the Impact of Cross-Sectional Variations in the Primary Flight Feather Shaft on Mechanical Properties

Primary flight feather shafts, a critical structural component of avian flight, exhibit excellent mechanical properties. The cross-sectional and medullary foam internal cavity structures of the feather shaft exhibit a gradual variation along the shaft; however, the mechanism by which this gradual variation influences the mechanical properties of the shaft remains unclear. In this study, the structural characteristics of a primary flight feather shaft were analyzed. Subsequently, the effects of gradual variations in the cross-sectional shape and medullary foam internal cavity structure along the shaft on its buckling resistance, torsional stiffness, and bending behavior were investigated. The experimental results showed that, along the length of the primary flight feather shaft, its cross-sectional shape transitions progressively from circular to approximately pentagonal and finally to quadrilateral, while its medullary foam cavity structure gradually changes from a circular to an inverted triangular shape. Feather shafts with an approximately pentagonal cross-section and an elliptical medullary foam cavity structure exhibit excellent buckling resistance, torsional resistance, and bending stability. Finally, based on the structural characteristics of the feather shaft, bionic samples with different cross-sectional shapes and medullary foam cavity structures were fabricated using fused deposition modeling (FDM), and their bending properties were assessed through three-point bending tests. The experimental results demonstrated that the bioinspired prototype, featuring an approximately pentagonal cross-section and an elliptical medullary foam cavity structure exhibited optimal bending properties, achieving a maximum specific load-bearing capacity of 102.64±1.66 N/g. This study provides bio-inspired insights into the design of lightweight structures.