Abstract: A support structure for an aircraft includes a structural member having a generally planar shape, a longitudinal axis defining a longitudinal direction and a transverse axis orthogonal to the longitudinal axis, and a plurality of rounded holes formed along the longitudinal direction. Each rounded hole has a respective major axis with a major length and a minor axis orthogonal to the major axis with a minor length that is less than the major length. Each rounded hole is oriented with its major axis rotated more than 0 degrees and less than 90 degrees from the longitudinal axis of the structural member. The structural member is configured for bearing external loads acting on the structural member in a principal loading direction that is not parallel with the longitudinal axis or the transverse axis. Each rounded hole may be oriented with its major axis aligned generally parallel with the principal loading direction.

Abstract: Composite skin-stringer structures which reduce or eliminate the risk of delamination at the skin-stringer interface. This can be accomplished by arranging ply directions (i.e., the angles of the fiber paths of the ply) in a layup in a way such that for the dominant loading, the skin and stringer will each deform in a way that reduces relative opening (fracture Mode I) and/or sliding (fracture Mode II) and/or scissoring (fracture Mode III) at the skin-stringer interface. This is possible when coupling between specific deformations modes is purposefully activated instead of being suppressed. The ply directions in the stringer are adjusted so that the stringer deforms in a controlled fashion to suppress or “close” cracks that are about to form—before the undesirable modes of failure form—as load is applied.

Abstract: A design process that uses lamination parameter inversion to generate a set of baseline layups having desired stiffness properties. Then the underdetermined Newton's method can be applied to explore solution manifolds describing alternative designs having similar if not identical stiffness properties. The manifold of solutions can be methodically examined to find those with desirable properties. Desirable properties include those that have been traditionally captured by design rules or those that improve manufacturability. Combining lamination parameters as design variables with lamination parameter inversion provides an efficient optimization process for non-traditional laminates.

Abstract: A method of generating an optimized design model for a composite laminate may include computing a normalized set of lamination parameters and laminate stiffness matrices of an initial laminate design, and determining, using an optimizer operating on a finite element model, optimum values for the lamination parameters and the laminate thickness. The method may further include adjusting the optimum value of the laminate thickness, and performing an inversion process extracting multiple solutions from the lamination parameters, each solution including a unique set of individual fiber angles for each ply and representing an optimized design model of the composite laminate.

Abstract: A design process that uses lamination parameter inversion to generate a set of baseline layups having desired stiffness properties. Then the underdetermined Newton's method can be applied to explore solution manifolds describing alternative designs having similar if not identical stiffness properties. The manifold of solutions can be methodically examined to find those with desirable properties. Desirable properties include those that have been traditionally captured by design rules or those that improve manufacturability. Combining lamination parameters as design variables with lamination parameter inversion provides an efficient optimization process for non-traditional laminates.

Abstract: Composite skin-stringer structures which reduce or eliminate the risk of delamination at the skin-stringer interface. This can be accomplished by arranging ply directions (i.e., the angles of the fiber paths of the ply) in a layup in a way such that for the dominant loading, the skin and stringer will each deform in a way that reduces relative opening (fracture Mode I) and/or sliding (fracture Mode II) and/or scissoring (fracture Mode III) at the skin-stringer interface. This is possible when coupling between specific deformations modes is purposefully activated instead of being suppressed. The ply directions in the stringer are adjusted so that the stringer deforms in a controlled fashion to suppress or “close” cracks that are about to form—before the undesirable modes of failure form—as load is applied.

Abstract: A method of configuring a composite laminate may include selecting at least two different material systems for the laminate. Each one of the material systems may have material properties and corresponding material invariants. The laminate may be comprised of a stack of plies having a stacking sequence. The method may include characterizing the stacking sequence using lamination parameters for each material system. The method may further include calculating a transverse shear stiffness of the laminate using the material invariants and the lamination parameters.