Composite Stringer Reinforcement via Localized Ply Stacking
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Solution Overview
Problem
Current manufacturing techniques for aircraft stringers fail to provide effective reinforcement across the entire profile, particularly at the foot and web, leading to structural inefficiencies and increased risk of damage from impacts, as they require significant process modifications and result in incomplete reinforcement due to fabric superposition and demolding issues.
Innovation Solution
The integration of independent reinforcement areas in the foot and web of the stringer, achieved by stacking reinforcing plies alongside continuous plies, allowing for a localized widening of the section that extends from the edge to an internal termination, forming a compact block that is embedded within the stringer, thereby enhancing structural integrity and impact resistance without substantial modifications to the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If reinforcing elements are manufactured separately and placed in channels formed by bending the sheet, then reinforcement is provided at the head of the web, but the process requires great modification of manufacturing process and tool, and the reinforcement does not extend to the very edge of the head of the web
Solution Approach 1:
The invention merges the reinforcement manufacturing with the basic stringer manufacturing process. Reinforcing plies are stacked together with continuous plies in a single planar configuration before shaping, eliminating the need for separate reinforcement manufacturing and placement steps. This integration resolves the contradiction by providing full-edge reinforcement without requiring great modification of the manufacturing process.
Solution Approach 2:
The invention performs the reinforcement integration in advance during the planar stacking phase, before the stringer is shaped into its final L-shaped or T-shaped configuration. By pre-positioning reinforcing plies alongside continuous plies in the flat state, the reinforcement automatically extends to the very edge of the head of the web after shaping, without requiring subsequent modifications to the manufacturing process.
2Strength
If multiple reinforcements are placed in the foot and web using conventional techniques, then reinforcement coverage is increased, but fabric superposition occurs in the radius area which accumulates defects
Solution Approach 1:
The invention applies local quality by providing reinforcement only where structurally necessary, with reinforcing plies positioned to extend from the free edge to an internal termination edge. This localized approach avoids unnecessary fabric superposition in the radius area while maintaining reinforcement coverage in critical zones, thereby preventing defect accumulation while preserving strength.
Solution Approach 2:
The invention segments the reinforcement into distinct reinforcing plies that are independently positioned and terminated. This segmentation allows precise control over where reinforcement ends, preventing the superposition of multiple fabric layers in the radius area while maintaining adequate reinforcement coverage in the foot and web regions.
3Shape
If the stringer profile is shaped into L-shaped or T-shaped configuration, then structural functionality is achieved, but demolding problems occur with I-shaped or J-shaped profiles due to complex mold requirements
Solution Approach 1:
The invention performs all ply stacking and reinforcement integration in the planar state before shaping. By completing the entire laminate assembly in the flat configuration, the subsequent shaping into L-shaped or T-shaped profiles becomes a simple forming operation without complex mold requirements, avoiding demolding problems entirely.
Solution Approach 2:
The invention merges the reinforcement placement and stringer formation into a single integrated process. Both continuous plies and reinforcing plies are stacked together in the planar state and then shaped simultaneously into the final profile, eliminating the need for separate reinforcement installation steps and complex multi-stage molding processes.
Data Source
AI summary
The present invention relates to a stringer, particularly to a stiffening and structural longitudinal element for skin of aircraft airfoil surfaces, characterized in that it incorporates two separate and independent reinforcement areas, one in the foot and the other at the end of the web (head) of the stringer, where the reinforcement areas are obtained by a widening of the section of the stringer, the widening being formed by a localized stack of reinforcing plies of composite material which are embedded within the stringer. The invention also relates to the method of manufacture and is particularly applicable to stringers having an L-shaped or T-shaped section.