Aircraft Stringer Run-Out Joint Strength via Ply Embedding
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Solution Overview
Problem
Conventional methods for transferring load between stringers and skin panels in aircraft composite structures often result in de-bonding issues due to shear and peeling effects, which are costly and complex to address, requiring additional components or substantial manufacturing process modifications.
Innovation Solution
The integration of the stringer's foot into the skin panel by inserting it between plies of composite material, allowing for co-bonding or co-curing, thereby increasing the interface area and enhancing the joint strength without additional components or process modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional stringer bonding methods are used to join stringer to skin panel, then the manufacturing process is simple, but de-bonding problems occur due to shear and peeling effects at the stringer run-out section
Solution Approach 1:
The stringer foot is inserted between plies of the skin panel, transitioning from a surface-level bonding interface to a three-dimensional embedded configuration. This dimensional change allows the stringer foot to be surrounded by composite material on multiple sides, creating superior mechanical interlocking and load transfer paths that prevent de-bonding while maintaining manufacturing simplicity through co-curing or co-bonding processes
2Reliability
If additional components such as metallic brackets or bolts are used to enhance load transfer at the stringer run-out section, then de-bonding problems are mitigated, but the manufacturing process becomes more complex and expensive
Solution Approach 1:
The stringer foot and skin panel are merged into a single integrated composite structure through co-curing or co-bonding processes. The stringer foot is embedded between plies of the skin panel, eliminating the need for separate metallic brackets or bolts. This merging creates a unified load transfer path where the interface area between the stringer foot and surrounding plies provides sufficient bonding strength without additional components
Solution Approach 2:
The solution uses composite material properties to achieve superior joint strength. The stringer foot, made of composite material, is embedded within the composite plies of the skin panel, creating a homogenous load transfer interface. This composite-to-composite bonding eliminates the need for metallic fasteners or brackets, simplifying the structure while maintaining or enhancing load transfer capability
Data Source
Figure 1~2A
Figure 2B~3
Figure 4
AI summary
Composite structure for an aircraft comprising a skin panel (1) and at least one stringer (3) joined to a surface of the skin panel, the stringer having a foot (4) and a web (2) protruding from the foot, and a run-out section (5) at one of its ends. The panel includes a plurality of stacked and co-cured plies (9, 10) of composite material, and at least part of the foot of the stringer at the run-out section, is inserted between two plies of the panel, and it is co-bonded, co-cured or secondary bonded with said two plies. The structure described provides a reinforced join between the foot of the stringer and the skin panel, avoiding peeling or de-bonding problems, without substantially modifying the manufacturing process.