Hat Stringer Recess Design for Composite Void Reduction
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Solution Overview
Problem
Conventional hat-shaped stringers lack sufficient off-axis directional strength and are prone to collapse under high loading conditions due to voids and stress concentrations at the juncture areas between the reinforcement assembly and the composite skin structure, requiring additional gap fillers that complicate the manufacturing process and increase costs.
Innovation Solution
A hat-shaped stringer design featuring a cap portion with recessed flanges and composite walls positioned within the recess, optimizing the placement of reinforcement assemblies to minimize voids and enhance off-axis strength, using a method that involves laying up composite plies and positioning composite walls to intersect the cap portion and flanges, thereby reducing the likelihood of cracking and manufacturing complexities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a trapezoidal cross-sectional reinforcement assembly is positioned internally within the hat-shaped stringer cavity, then the stringer gains internal reinforcement capability, but voids and stress concentrations are created at the juncture areas between the reinforcement assembly and the composite skin structure
Solution Approach 1:
The patent applies local quality by creating a recess in the cap portion of the hat-shaped stringer specifically at the juncture areas where the flanges meet the skin structure. This recess is positioned to eliminate voids and stress concentrations at these critical locations, while the rest of the reinforcement assembly maintains its trapezoidal cross-section for structural support. The recess is formed by removing material from the cap portion to create a localized modification that addresses the specific problem area without altering the overall reinforcement geometry.
2Reliability
If gap fillers are employed to fill voids created by the reinforcement assembly geometry, then cracking is prevented, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies the extraction principle by removing the need for gap fillers entirely. Instead of adding material to fill voids, the invention extracts or removes material from the cap portion to create a recess that eliminates the voids in the first place. This approach reverses the conventional method of adding gap fillers and instead focuses on removing unnecessary material that would create voids, thereby simplifying the manufacturing process while maintaining reliability.
3Reliability
If gap fillers with different material properties are used to fill voids, then voids are eliminated, but cure cycles and processing parameters must be modified
Solution Approach 1:
The patent eliminates the need for gap fillers by extracting or removing material from the cap portion to create a recess that prevents void formation. This approach removes the entire gap filler subsystem, including all associated material compatibility issues, cure cycle modifications, and processing parameter adjustments. By eliminating the problem rather than treating it, the manufacturing process maintains its original time and parameter requirements.
4Shape
If the reinforcement assembly uses right angled corner turns adjacent to the composite skin structure, then structural geometry is simplified, but voids are created at the juncture areas
Solution Approach 1:
The patent applies local quality by modifying only the cap portion at the juncture areas where the flanges meet the skin structure. The recess is created locally in the cap portion to eliminate voids at these specific critical locations, while the rest of the reinforcement assembly maintains its simple trapezoidal geometry with right angled corner turns. This localized modification preserves the overall geometric simplicity while addressing the specific void formation problem at the junctures.
Data Source
AI summary
A hat-shaped stringer includes wrap of at least one composite ply which includes cap portion and first flange which extends from a first side of the cap portion and second flange which extends from a second side of the cap portion, wherein the cap portion defines a recess positioned between the first and second flanges. Further included is a first composite wall which extends in a first direction along a first plane within the recess, wherein the first plane intersects the cap portion and intersects a skin positioned between the first and second flanges to which first and second flanges are secured and opposing sides of the first composite wall are spaced apart from the cap portion. First composite wall is connected to a second composite wall, which extends along the cap portion, are a portion, for example, of a triangular formation having radial portions.