Available at: https://digitalcommons.calpoly.edu/theses/2049
Date of Award
MS in Aerospace Engineering
Composites have high strength-to-weight ratios, which is particularly desired for applications with weight restrictions. Common composite materials such as carbon fiber reinforced plastic (CF) and fiber glass reinforced plastic (FG) were used in this research. While composite materials possess high stiffness and strength properties, the stiffness of composite laminates may be maximized by changing the geometry. By adding corrugations, the flexural stiffness is increased in one direction compared to the stiffness of a flat part with the same amount of material. Thus, stiffness increases without a change in weight. The primary goal of this research was to investigate the stiffness characteristics of corrugated composite laminates under tensile and flexural load. The chosen corrugation geometry for investigation was a trapezoid. To observe the effects of corrugations, both flat and corrugated coupons were tested experimentally with the same procedures. Stiffness was calculated experimentally, analytically, and numerically in both directions. In this study, the longitudinal direction was defined as perpendicular to the corrugations and transverse direction was defined as the direction along the corrugations. The effects on stiffnesses of corrugated and flat composites were measured by comparing changes to the stiffness ratios in tension and bending. The stiffness ratio is the ratio of longitudinal stiffness to transverse stiffness. The secondary aim of this research was to compare the corrugation effects on FG weave and cross-ply CF. This was interesting to observe the difference in corrugation effects on different composite materials. The FG laminates were manufactured from four plies of pre-impregnated Cytec MXB 7701/7781. The CF laminate consisted of five plies of pre-impregnated unidirectional Tencate TC250/M46J. The layup orientation of the CF laminate had alternating 0◦ and 90◦ plies, where the 0 ◦ plies were in the transverse direction. Plies were directly laid on a flat plate and aluminum mold for flat and corrugated specimens, respectively. All flat and corrugated composites were cured in an autoclave under respective recommended cure cycles for each material. The tension and three-point bend tests were conducted on an Instron 8800 where the load was applied at a rate of 0.05 inches per minute. The tensile ultimate load was the same between corrugated and flat specimens in the longitudinal direction. Meanwhile, the tensile ultimate load was greatly reduced for corrugated specimens in the transverse direction when compared to the flat specimens. Thus, corrugations had a larger impact in the transverse direction under tensile load for both materials. By corrugating the composite layups, the ratio of stiffness in the longitudinal to extensional direction increases. For FG test coupons, the extensional stiffness ratio was increased from 1.0 to 49.3 due to corrugations. The flexural stiffness ratio was increased from 0.3 to 187.1 in corrugated FG coupons. For CF test coupons, the extensional stiffness ratio increased from 0.7 to 61.3. The flexural stiffness ratio of CF test coupons increased from 0.3 to 81.4. Corrugations had a greater effect on the cross-ply CF for both extensional and flexural stiffnesses.