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The AUS Repository serves as the Institutional Repository of the American University of Sharjah, providing open access to research outputs from AUS students and faculty. By preserving these works for the long term and increasing their global visibility, the repository plays a key role in the dissemination of knowledge. See our About Us page for more information.
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Item Novel Sandwich Panel Design Integrating Structural Reinforcements with Polymeric Foam(2024-06)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), analysing 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 30 mm 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.Item Assessment of bent and straight GFRP reinforcement conditioned in harsh environments(2024-06)This dissertation investigated the impact of durability on the strength of bent and straight GFRP rebars in harsh environments. The typical tensile strength observed in bent FRP rebars compared to the strength of straight rebars was on average lower by 40%, unlike conventional steel. There was a lack of studies on the durability of bent FRP bars in harsh environments like those in the UAE and Gulf region. To address this gap, two sets of durability tests were conducted, one indoors and another outdoors, with a specific focus on performance in saline environments. A comparative analysis was conducted among the results of control unconditioned samples, those exposed to the outdoor saline environment of the UAE, and those subjected to indoor accelerated durability setups in the laboratory. The aim was to identify any consistent patterns of strength deterioration in straight and bent GFRP rebars across these two testing setups (indoor and outdoor), as compared to control unconditioned specimens. The variables of the experimental program were GFRP rebar diameter, manufacturer, rebar shape, radius of curvature, durability setup, and aging duration. The results covered failure modes, load-deflection responses, strain measurements, tensile strength retention, and microstructure analysis of the GFRP rebars. Test results showed that GFRP rebars, whether straight or bent, demonstrated similar initial stiffness. However, load capacity and deflection variations were observed based on rebar size and exposure conditions. The microstructure analysis through SEM showed that the manufacturing bending process changed the cross-section of GFRP rebars from circular to approximately rectangular, which altered the load distribution and induced differential stresses along the rebar length. Additionally, environmental exposures caused notable fiber and fiber-matrix interface damage in the GFRP rebars. This study concluded that there was moderate retention of tensile strength, with an average of about 80% for the outdoor setup and 75% for the indoor accelerated setup over the exposure periods. Thus, nonmetallic GFRP reinforcement was a viable alternative to steel reinforcement in RC structures exposed to marine and harsh saline environments.
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