Composite Stringer End Trim Curvature Reduces Pull-Off Forces
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Solution Overview
Problem
In composite wing stringer structures, stress and strain concentrations occur at the ends due to offset splice plates, leading to potential delamination and increased pull-off forces, which existing technologies fail to adequately address.
Innovation Solution
A stringer end trim with one or multiple radii is implemented to reduce bending and axial stiffness at the stringer ends, distributing loads across a larger area and minimizing strain concentrations, using a double radius configuration for attachments through both flanges and a single radius for attachments through one flange.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the stringer end is solid from cap to base flange, then structural strength is maintained, but stress and strain concentrations increase at the stringer ends
Solution Approach 1:
The patent applies curved radii (single or multiple) at the stringer free edge instead of a sharp corner. This curvature distributes the stress and strain concentrations that would otherwise occur at the abrupt end of the stringer web, thereby reducing peak stresses while maintaining the overall structural strength of the solid stringer end configuration.
2Ease of manufacture
If splice plates are offset from the centroid load path, then joint attachment is achieved, but bending moments and pull-off loads increase at the stringer ends
Solution Approach 1:
The curved radii at the stringer free edge help distribute the pull-off loads induced by the offset splice plates. By creating a gradual transition rather than an abrupt end, the curvature reduces the concentration of forces at the stringer-end/skin-panel interface, allowing the offset splice plate configuration to be used without excessive localized loading.
3Stress or pressure
If multiple radii are used in the stringer end trim, then strain concentrations are reduced, but manufacturing complexity increases
Solution Approach 1:
The patent provides for either a single radius or multiple radii at the stringer free edge. The single radius option provides a simple curved transition that reduces strain concentrations. The multiple radius option provides enhanced strain distribution for applications requiring higher performance. Both options maintain relative manufacturing simplicity compared to more complex structural modifications.
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A stringer (2) having a stringer end trim (7) that reduces pull-off forces in a stringer connection structure, including a stringer body (9); a stringer free edge (8) provided on said stringer body (9); and a stringer end trim (7) having at least one curvature (10, 12, 14) provided in the stringer free edge (8) forming the stringer connection structure.