Additive Manufacturing (Potting) of Fiber-Reinforced Thermoset Sandwich Composite Structures: Fabrication, Numerical Simulation, and Structural Optimization

摘要

Sandwich composite structures are a distinct category of laminated composite materials with extensive applications in the aeronautical, civil, marine, and automotive industries. A sandwich structure constitutes a set of two stiff external face skins bonded to a thick central core of low density. Fiber-reinforced composites are the choice of materials for face skins while the core material comprises foam, honeycomb, or balsa wood. This thesis depicts an eccentric nozzle-based additive manufacturing (AM) technique based on potting to fabricate fiber-reinforced thermoset sandwich specimens. The conventional methods of manufacturing sandwich composites induce significant manual labour. These processes render high cost of fabrication, material waste, and restricted tailoring of designs. Recently, the infusion of additive manufacturing (AM) has garnered widespread attention for its potential to produce high-strength composites. This influx of AM can be attributed to its unprecedented attributes of tailorable design and flexible mechanical properties to produce functional components at a rapid pace and reduced cost. The objective of this thesis is to utilize the potential of AM to produce fiber-reinforced thermoset sandwich structures for high-strength applications. The research task comprises a sequential approach of initially developing 3D models of two sandwich mold specimens for mechanical characterization (a dog-bone and a rectangular bar). In this work, we adopted a commercial slicer software to develop a unique G-code generating the toolpath for extruding carbon fiber and epoxy face skin materials from a dispensing medium into the cured mold. The original framework of the thesis was then to bond commercially available foam to the face skin. We presented a proposed plan of action for performing 3-pont bending tests and tensile tests of sandwich structures to evaluate load-displacement data, tensile strength, etc. As a means to efficiently transition from manufacturing experiments to numerical simulation, the next part of this thesis presents Finite Element Analysis (FEA) studies to conduct numerical simulation and design optimization of sandwich-shaped structures for the aerospace industry. We performed numerical simulation of a 3-point bending test on a sandwich composite beam in ANSYS to evaluate the load-deflection behavior. Next, we used the built-in optimization module in ANSYS to perform design optimization of three novel structural designs for potential applications in the aerospace industry. The results yielded significant mass savings for all three configurations. Finally, the thesis presents comparative single-objective weight and cost-optimization studies of sandwich composites, carbon-epoxy, and aluminum alloy beams using the interior-point algorithm in MATLAB. The study yielded optimum cost and weight values for these beams within specified constraints. Overall, this work aims to manifest the significance of nozzle-based AM and Finite Element Analysis (FEA) to fabricate and optimize sandwich composite structures for the aerospace industry. Principal benefits include reduced cost, faster production, and improved fuel efficiency.