Identifying the Optimal Pitch Angles for Bouligand Structures

Abstract

The Bouligand structure is a typical helicoidal architecture found in various crustaceans in which each layer rotates by a small angle relative to the adjacent one. We present a theoretical analysis to relate the rotation pitch angle to the mechanical performance (interlaminar shear property in this case) of laminas mimicking the Bouligand architecture. Theoretical models representing the helicoidal composite laminate stacking sequences are compared against experimental tests carried out on 32-layer helicoidal carbon fibre laminates with pitch angles of 6°, 9.1°, 12°, 25.7° where the 9.1° is the predicted optimal angle. The results show that this particular architecture with a pitch angle of 9.1° indeed attains the highest load-bearing capability and delays any catastrophic delamination. We also examine the role played by the rotation angle on the mechanisms like crack twisting and branching that are responsible for the superior performance. These results provide a fundamental basis to the design of helicoidal structures mimicking the Bouligand architecture.