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COBEM 2021
26th International Congress of Mechanical Engineering
COMPARISON BETWEEN QUAD AND DOUBLE-DOUBLE LAMINATES IN THE BUCKLING DESIGN OF A CARBON/EPOXY WING STRUT
Submission Author:
Marília Attoni , MG
Co-Authors:
Marília Attoni, Carlos Alberto Cimini Junior
Presenter: Marília Attoni
doi://10.26678/ABCM.COBEM2021.COB2021-1830
Abstract
The strut-braced wing configuration has received prominence in the aeronautical industry recently, mainly due to the development of the Sugar Volt, partnership aircraft of Boeing and NASA. The structural configuration for the high elongation wing is a truss, called strut, which braces the wing to the fuselage. It is then possible to obtain wings with large wingspans and small thicknesses, thus aerodynamically and structurally optimized. However, the design of the strut becomes decisive for the viability of the configuration, mainly for buckling strength. In this scenario, the use of composite materials is a viable alternative to allow tailoring for buckling resistance without the substantial increase in mass. On the other hand, the conventional quasi-isotropic laminate used by the aeronautical industry called “quad” for having the orientations at four different directions (0⁰, ±45⁰, and 90⁰), must follow a series of design rules, including symmetry and balancing, that make the choice of the optimum laminate unfeasible. Amongst them, the 10% rule stands out, which requires that the final laminate present at least 10% of its layers in each one of these orientations. Despite not being formally documented in a standard, this restriction is a “thumb rule” adopted to guarantee a minimum portion of the laminate’s transversal stiffness. In addition, "quad" laminates are difficult to manufacture and do not allow the suppression of layers for weight relief (ply drop), since the removal of layers from the laminate not only alters its properties, but also make difficult to keep the symmetry and the balance. Thus, a new family of laminates called "double-double" (DD) was proposed, in which the layers have orientations [±phi/±psi], in which the angles phi and psi can assume any desired values, which allows continuous optimization laminate with less complexity, less mass and manufacturing advantages. Therefore, it was proposed in this work to compare the structural design of the strut in conventional laminates "quad" and DD using the composite carbon-epoxy material T300-F934, in which the truss is subjected to compressive uniaxial load. As a result, the "quad" laminate [0_56/+45_2/−45_2/90_4]s and the DD laminate [(±7/±16_8]s were obtained for the strut design in buckling, with mass increase of 28% for the "quad" and 14% for the DD with respect to the obvious optimal unidirectional laminate. Thus, the DD laminate presents an intermediate number of layers between the optimal unidirectional and the "quad" laminates and, although marginally, recomposes the stiffness and strength of the “quad”.
Keywords
strut braced wing, Sugar Volt, Buckling, quad laminates, double-double laminates, design rules
