STRUCTURAL DESIGN OF HYBRID COMPOSITE SANDWICH SYSTEMS: A DESIGN METHODOLOGY FOR LAYUP OPTIMIZATION, LOAD TRANSFER ENHANCEMENT, AND INTEGRATION OF ADDITIVELY MANUFACTURED INSERTS IN MECHANICAL JOINTS

Abstract

To expand into non-traditional industries, sandwich composites must be competitive with metals in terms of material, production, operating, and ecological costs. This requires continued cohesive advancements in raw materials, production technology, and design methods. The objective of this dissertation is to enhance sandwich composite design methods through advanced material selection charts and to improve production and component technology by refining mechanical bonding insert designs and core splice configurations. This is achieved by introducing innovative and efficient sandwich composite material selection charts and showcasing the effectiveness of a novel 3D printed insert design and optimized core splice configurations that deliver low stress and high strength. The material selection charts developed in this research allow the user to define all parameters required to fully specify a sandwich composite including the number of plies per facesheet, the stacking sequence of those plies, the core thickness, and the core density for specific loading configurations. An overview of a finite element modeling approach that can be applied to thick-section sandwich composites is detailed and correlated to experimental results which allows the analyst to leverage an approach that is conducive to modeling when rapid design iterations are occurring such as in a research and development environment. The 3D printed insert design detailed in this study substantially outperforms standard inserts that are currently available on the market with a 59% increase in maximum pull-through force and 184% increase in maximum single-lap shear force while maintaining the same level of bolt preload loss as that seen in typical carbon fiber reinforced laminates. Finally, a numerical investigation of core splice methods is reviewed which shows that a discontinuous core butt-joint can be improved by adding plies to the facesheets or increasing the core thickness. Additionally, core splicing methods using a unique dovetail design are explored numerically. Findings from this numerical investigation show there is an optimized range of dovetail heights and tenon angles that lower maximum principal stresses and maximum shear stresses in the splice material and the core/splice interface, respectively when compared to traditional core splice joints.