PhD Dissertation Final Oral Defense (June 2024)

Title of dissertation: NOVEL SANDWICH PANEL DESIGN INTEGRATING STRUCTURAL REINFORCEMENTS WITH POLYMERIC FOAM
Name of Candidate: Assil Charkaoui
Name of Supervisor: Dr. Noha Mohamed Hassan Hussein / Dr. Zied Bahroun
Program: PhD in Materials Science and Engineering

Abstract
Sandwich panels, with their exceptional strength-to-weight ratio and energy absorption capabilities, are indispensable in many engineering applications. However, enhancing their impact protection and crashworthiness is becoming more pronounced. This research investigates the synergistic effects of various core topologies and fillings to enhance energy absorption capacities. This involved exploring variations in the core structure by comparing different unit cell shapes (X-frame, octet strut, H-frame, I-frame, and rhombus) and topological features (core volume fraction, core height, number of core layers, and unit cell direction), analyzing functionally graded sandwich panels, and studying different core fillers. The study examined different materials for core filling, such as resin, silicon and foam. The resin core filler was also strengthened with CNT to improve performance. A comprehensive Design of Experiments (DOE) approach was employed to explore the synergistic effects of the different variables. Numerical experiments were conducted using ABAQUS/CAE based on the experimental setup of a drop tower test. Regression analysis was used to investigate the numerical model responses and develop regression equations. Optimization techniques were then used to determine the optimum design parameters that maximize energy absorption using GAMS software. The optimization results showed that the X- frame core in the transverse direction with a volume fraction of 20% and a total core height of 30mm provides the best combination for increasing energy dissipated in damage and recoverable strain energy while minimizing the overall mass of the structure. Moreover, results demonstrated the foam’s ability to enhance energy absorption capabilities in X-frame sandwich panels. The optimal X-frame design was integrated with a foam filler, enhancing the energy absorption capabilities further.

Additionally, the functionally graded core of the X-frame sandwich panels, graded in the x-axis from the most to the least number of unit cells across three layers, showed a significant increase in energy absorption. Although resin-filled sandwich panels exhibited a brittle nature, the addition of CNT prevented perforation and significantly decreased the damage area on the sandwich panel. This research contributes valuable insights into the design and optimization of sandwich panels for enhanced impact resistance.

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