Structural Response of the Slotted Waveguide Antenna Stiffened Structure Components under Compression

The Slotted Waveguide Antenna Stiffened Structure (SWASS) is an aircraft system that can provide the capabilities of a stiffened panel skin structure and a slotted waveguide radar antenna simultaneously. The system made from carbon fiber reinforced polymers is designed around a 10 GHz radar frequency in the X-band range and uses a WR- 90 waveguide as a baseline for design. The system is designed for integration into fuselage or wing sections of intelligence, surveillance, and reconnaissance (ISR) aircraft and would increase the system performance through the availability of increased area and decreased system weight. Elemental parts of the SWASS structure were tested in compression after preliminary testing was completed for material characterization of a resin reinforced plain woven carbon fiber fabric made from Grafil 34-700 fibers and a Tencate RS-36 resin with a resin mass ratio of 30%. Testing included finite element stress and strain field characterization of seven single slot configurations, and results showed the longitudinal 90- slot was the best structural slot by about 30% in terms of maximum von Mises stress. Single waveguides were tested in the non-slotted configuration and a configuration including a five longitudinal slot array in one waveguide wall. Finite element results were compared with experimental results and showed good comparisons in all areas. The slot array was determined to have a decrease in nonlinear limit load of 8% from the finite element simulations and 12% from the experimental results. All waveguides showed the characteristics of local wall buckling as the initial failure mechanism and had significant buckling features before ultimate material failure occured.