Composite Stringer Run-Out Stiffness Reduction via 90° Ply Orientation
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Solution Overview
Problem
Conventional methods for manufacturing aircraft components with composite materials face challenges at stringer run-outs, where load transfer issues lead to stress concentration and potential detachment, with existing solutions either reducing stringer efficiency or complicating the manufacturing process.
Innovation Solution
Introducing plies at 90° adjacent to stringer run-outs, overlapping existing 0° plies, and progressively eliminating 0° plies to replace them with 90° plies, maintaining structural continuity and reducing elastic modulus without altering existing design or manufacturing standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the stringer cross-sectional area is reduced to decrease stiffness at run-outs, then the load transfer stress is reduced, but the stringer efficiency and buckling resistance are compromised
Solution Approach 1:
The patent applies local quality by changing the fiber orientation specifically at the run-out region while maintaining the original 0° orientation in the main stringer body. This is achieved by introducing plies with fibers oriented at angles between 45° and 90° to the stringer longitudinal axis in a localized zone adjacent to the run-out, where these angled plies progressively replace the 0° plies. This localized modification reduces the elastic modulus only where needed for load transfer, while preserving the high stiffness and strength of the main stringer structure for buckling resistance.
2Stress or pressure
If the number of plies is progressively reduced towards the run-out to decrease thickness and stiffness, then the load transfer stress is reduced, but manufacturing defects arise during compaction and cobonding
Solution Approach 1:
The patent applies parameter changes by modifying the fiber orientation angle parameter rather than changing the number of plies. Instead of progressively reducing the ply count towards the run-out (which causes manufacturing defects), the invention introduces plies with fibers oriented at angles between 45° and 90° that progressively replace the 0° plies in the run-out region. This parameter change (fiber orientation angle) achieves the desired reduction in elastic modulus and load transfer stress while maintaining adequate ply thickness for proper manufacturing quality during compaction and cobonding operations.
3Stress or pressure
If different types of plies with different elastic moduli are used at the run-out, then the stiffness is reduced, but the manufacturing process is excessively complicated
Solution Approach 1:
The patent applies local quality by implementing a localized ply arrangement specifically at the run-out region. In this localized zone, plies with fibers oriented at angles between 45° and 90° are introduced to progressively replace the 0° plies, reducing the elastic modulus only where needed. The main body of the stringer maintains its conventional ply structure with fibers oriented at 0° to the longitudinal axis. This localized modification achieves the desired stiffness reduction for load transfer while avoiding the need to complicate the entire manufacturing process throughout the stringer.
Data Source
AI summary
A stringer made of composite material for reinforcing aircraft skin panels. Plies are introduced at 90° in a segment close to the stringer run-out, and progressively reducing the number of plies at 0°, such that the majority of the number of plies is at 90° in an segment adjacent to the run-out, so the stiffness of the run-out is reduced, and the load it supports is also therefore reduced. This is an alternative solution to the solutions already existing for getting the stringer run-outs to support a smaller load, thereby reducing both the risk of the plies of the stringer peeling off and the risk of separation between stringer and skin panel. A method of manufacturing said stringer is also provided.