Composite Stringer Tapered Ply Termination
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Solution Overview
Problem
Existing stringer termination geometries in aircraft structures, whether metallic or composite, fail to fully exploit the benefits of composite materials, leading to local stress concentrations and separation of panels and stringers at termination points, necessitating additional reinforcement measures like finger plates or increased bolting.
Innovation Solution
A laminated composite stringer with a tapering stack thickness at the termination, achieved by consecutively terminating internal plies, which allows for controlled and even load distribution, reducing stress concentrations and potentially eliminating the need for additional reinforcement, and can be formed using fibre-reinforced laminates with a taper in both flange and web directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional stringer termination geometries are used, then the stringer can be terminated at obstructions, but local stress concentrations occur and panel/stringer separation tends to happen
Solution Approach 1:
The patent applies local quality by creating a tapered region specifically at the stringer termination zone where the ply stack thickness gradually reduces. This localized geometric modification concentrates the load transfer function in the taper region, creating a smooth stress gradient that eliminates stress concentrations while maintaining the ability to terminate at obstructions
Solution Approach 2:
The patent employs curved surfaces by replacing the traditional sharp termination edge with a smoothly tapered geometry. The continuous curved transition of the ply stack thickness eliminates abrupt geometric discontinuities, distributing stresses evenly and preventing the stress concentrations that lead to panel/stringer separation
2Strength
If stringer foot or finger plate reinforcement is added, then resistance to separation improves, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent extracts the load transfer function from separate reinforcement components (finger plates, cover plates) and integrates it directly into the stringer structure itself through the tapered ply stack. This eliminates the need for additional discrete parts while maintaining the strength to prevent separation
Solution Approach 2:
The patent merges the load transfer function with the stringer termination geometry by creating an integrated tapered structure. The taper itself performs the load distribution function that previously required separate reinforcement components, simplifying the overall structure and reducing manufacturing complexity
3Stress or pressure
If web taper is used to facilitate load transfer, then local stress concentrations are relieved, but the stringer geometry becomes more complex
Solution Approach 1:
The patent segments the stringer ply stack into distinct regions with different thicknesses - a full-thickness region and a tapered termination region. This segmentation allows the stress relief function to be localized to the taper zone while the main stringer body maintains its simple geometry and structural efficiency
Data Source
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AI summary
A laminated composite stringer having a termination at one end in its longitudinal direction, and including a laminated stack of composite structural plies, wherein internal plies in the stack are terminated consecutively towards the stringer termination to provide a taper of reducing stack thickness. Also, a composite structure comprising a panel and the stringer; and a method of manufacturing the stringer. The composite structure may be used in aircraft.