Effect of stiffness characteristics on the response of composite grid-stiffened structures

A study of the effect of stiffness discontinuities and structural parameters on the response of continuousfilament grid-stiffened flat panels is presented. The buckling load degradation due to manufacturing-introduced stiffener discontinuities associated with a filament cut-and-add approach at the stiffener intersections is investigated. For practical discontinuity sizes, the reduction in buckling load is negligible. The degradation of buckling resistance in isogrid flat panels subjected to uniaxial compression, combined axial compression, shear loading conditions, and induced damage, is quantified using finite element analysis. The combined loading case is the most critical one. The benefit of utilizing nonsolid stiffener cross sections is evaluated. Nonsolid stiffener cross sections, such as a foam-filled blade or hat with a 0-deg dominant cap, result in grid-stiffened structures that are structurally very efficient for wing and fuselage applications. The results of a study of the ability of gridstiffened structural concepts to enhance the effective Poisson's ratio of a panel is presented. Grid-stiffened concepts create a high effective Poisson's ratio which can produce large camber deformations for certain elastic tailoring applications.