Composite Stringer with Variable Gage and Overwrap
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Solution Overview
Problem
Conventional composite stringers in aircraft have excess gage in skin flanges and webs, leading to increased weight and manufacturing costs, as well as delamination issues due to stiffness mismatches between the stringer and the support structure.
Innovation Solution
A composite stringer design with varying gages and constant radii of curvature, where the top flange has a greater gage than the skin flange and web, and an overwrap layer is used to mitigate delamination and reduce the size of the radius filler, thereby improving strength-to-weight ratio and simplifying manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional composite stringers use uniform gage in skin flanges and webs, then manufacturing is simpler, but weight increases and strength-to-weight ratio decreases
Solution Approach 1:
The patent applies local quality by varying the gage (thickness) of different portions of the composite stringer. Specifically, the skin flange has a first gage, the web has a second gage, and these gages are different to optimize structural efficiency. This allows thinner sections where less strength is needed, reducing overall weight while maintaining manufacturing feasibility through standardized composite layup processes.
2Ease of manufacture
If conventional composite stringers use uniform gage, then manufacturing is simpler, but strength-to-weight ratio decreases
Solution Approach 1:
The patent implements local quality by assigning different gages to different portions of the stringer based on their structural requirements. The skin flange and web have different gages optimized for their specific load paths, maximizing the strength-to-weight ratio. This is achieved through controlled variable thickness in the composite laminate structure.
Solution Approach 2:
The patent applies parameter changes by varying the gage parameter across different portions of the composite stringer. The skin flange has a first gage value while the web has a second gage value, allowing optimization of mechanical properties for each region's specific stress state, thereby improving overall strength-to-weight ratio.
3Ease of manufacture
If skin flange and web have similar gage, then manufacturing is simpler, but delamination occurs due to stiffness mismatch
Solution Approach 1:
The patent addresses delamination resistance through local quality by giving the skin flange and web different gages that better match their respective stiffness requirements. This reduces the stiffness mismatch at the junction, minimizing delamination risks while maintaining manufacturing simplicity through standardized composite fabrication methods.
4Weight of moving object
If radius filler size is reduced, then weight decreases, but delamination mitigation capability decreases
Solution Approach 1:
The patent applies parameter changes by optimizing the gage values of the skin flange and web to reduce stiffness mismatch, which in turn reduces the required size of the radius filler for effective delamination prevention. This allows weight reduction while maintaining delamination mitigation capability through improved baseline structural design.
Data Source
AI summary
In an example, a composite stringer assembly includes a composite stringer, a radius filler, and an overwrap layer. The composite stringer includes: (i) a skin flange configured to be coupled to a support structure, (ii) a web, (iii) a lower corner portion of the composite stringer extending from the skin flange to the web, and (iv) an inner surface of the composite stringer extending along the skin flange, the lower corner portion, and the web. The radius filler includes a first surface coupled to the inner surface at the lower corner portion, a second surface configured to couple to the support structure, and a third surface extending between the first surface and the second surface. The overwrap layer is coupled to the inner surface at the web, the third surface of the radius filler, and the support structure.