The Mechanical Response of Geometrically Tailored Honeycombs with Sandwich Cell Walls

Abstract

Advances in additive manufacturing have enabled the development of novel honeycomb designs with unique mechanical and functional attributes. Generally, the in-plane mechanical response of honeycombs is bend-dominated due to their intrinsic design, where the cell walls incur bending moments during uniaxial or shear loading. Integrating sandwich beams into the unit cell design increases the bending stiffness, leading to a stiffer and stronger honeycomb structure. This thesis is concerned with the design and fabrication of sandwich-structured honeycombs (SSHCs) and an in-depth investigation of their elastic-plastic behavior through analytical, numerical, and experimental approaches. An analytical model was developed to formulate closed-form solutions of the elastic constants by combining classical honeycomb mechanics with an extended sandwich beam theory. The elastic-plastic response of the SSHC under in-plane uniaxial, biaxial and shear loading was also investigated. The SSHC was found to collapse by three competing mechanisms: core shear, face yielding, and elastic buckling, based on the honeycomb architecture and the properties of the materials involved. Detailed finite element (FE) calculations were performed to validate the analytical predictions of the effective elastic constants and the collapse response, showing excellent agreement with numerical predictions. The main findings suggest substantial performance enhancements relative to the mass equivalent monolithic honeycomb, with at least 200% increase in stiffness and collapse stress achieved for certain SSHC designs. Lastly, additive manufacturing (AM) techniques were explored to investigate the feasibility of manufacturing the SSHC for experimentation, confirming the predictive capabilities of the developed models through experimental observations and measurements.

Date of Award	19 Jul 2024
Original language	American English
Supervisor	Andreas Schiffer (Supervisor)