Composite Skin-Stringer Layups Using Mode Coupling Against Delamination
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Solution Overview
Problem
Composite skin-stringer structures in aircraft are susceptible to interfacial delamination, which compromises structural integrity, and existing solutions like increasing thickness or redesigning structures lead to weight penalties and increased costs.
Innovation Solution
Adjusting ply directions in the stringer to cause controlled deformation and suppress delamination by coupling specific deformation modes, using steered fiber technology to fabricate the stringer and optimize laminate stacking sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional design rules (balance or symmetry) are used in composite layups, then undesired failure modes and coupling effects are avoided, but the stacking sequences are restricted
Solution Approach 1:
The patent applies asymmetry by deliberately using unsymmetric stacking sequences in composite laminates to achieve desired coupling effects and deformation behaviors. This resolves the contradiction by showing that controlled asymmetry can provide both reliability through targeted failure mode management and versatility in stacking sequence design, rather than relying on traditional symmetric constraints
2Reliability
If the thickness of stringer and/or skin is increased at a trouble spot, then delamination resistance is improved, but weight penalty occurs
Solution Approach 1:
The patent applies local quality by implementing tailored stacking sequences and ply orientations at specific locations (trouble spots) rather than uniformly increasing thickness throughout the structure. This allows delamination resistance to be improved locally through optimized laminate design while avoiding unnecessary weight penalties in other areas
Solution Approach 2:
The patent changes material parameters (ply angles, stacking sequence, laminate configuration) rather than simply increasing thickness. By adjusting these parameters, the structure achieves improved delamination resistance through optimized mechanical properties and deformation characteristics without the weight penalty associated with thicker sections
3Reliability
If the skin and stringers are redesigned next to the problem area, then load diversion from the trouble spot is achieved, but manufacturing costs and additional redesign time increase
Solution Approach 1:
The patent applies preliminary action by designing optimized stacking sequences and ply orientations during the initial design phase to prevent delamination issues before they occur. This eliminates the need for costly redesigns and manufacturing changes later, as the structure is inherently resistant to delamination through its laminate configuration
Data Source
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AI summary
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.