Fastener Locking Member Cavity for Composite Lightning Protection
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Solution Overview
Problem
Drilling fastener holes in composite materials leads to defects like fiber fracture and delamination, and composite structures are susceptible to lightning damage due to their anisotropic nature and electrical conductivity, necessitating improved fastener solutions for aircraft applications.
Innovation Solution
A locking member with a containment cavity that reduces internal pressure during lightning strikes and provides an intimate seal with the composite structure, featuring a shank portion, flanged portion, and a bore with specific inner wall geometries to enhance compliance and prevent hot particle ejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fasteners are used in composite structures, then the fastening function is achieved, but delamination occurs between plies during installation and operation
Solution Approach 1:
The patent introduces a compliance element between the fastener and composite structure that anticipates and cushions against installation and operational loads. This element deformable under load prevents sudden stress transmission to the composite plies, thereby preventing delamination before it occurs during fastener installation and operation.
Solution Approach 2:
The patent changes the mechanical parameters of the fastener system by introducing an element with specific compliance characteristics. This element has controlled stiffness and deformability that allows it to absorb installation loads and distribute operational stresses, transforming the rigid fastening system into a compliant one that protects against delamination.
2Strength
If fasteners are installed in composite structures, then mechanical joining is achieved, but hot particle ejection occurs during lightning strikes
Solution Approach 1:
The patent introduces a containment cavity as an intermediary space between the fastener and the composite structure. During lightning strikes, this cavity captures and contains hot particles generated at the fastener-structure interface, preventing their ejection into the surrounding environment while maintaining the mechanical joining function.
Solution Approach 2:
The patent converts the harmful effect of hot particle generation during lightning strikes into a contained phenomenon. By designing the containment cavity to capture these particles, the system transforms a potentially dangerous ejection event into a controlled containment scenario, protecting the surrounding structure and environment.
3Weight of moving object
If composite structures are used for light weight, then weight reduction is achieved, but susceptibility to lightning damage increases
Solution Approach 1:
The patent employs a hybrid approach combining metallic fasteners with composite structures, where the metallic elements provide lightning current pathways and the composite provides weight reduction. The containment cavity design specifically addresses the interaction between metallic fasteners and composite materials during lightning strikes, managing hot particle generation at the interface.
Solution Approach 2:
The containment cavity acts as an intermediary protective feature that manages the lightning strike effects in hybrid composite-metallic structures. It provides a controlled environment for current dissipation and hot particle containment, enabling the use of lightweight composites while mitigating their increased lightning susceptibility.
4Ease of manufacture
If drilling is used to create fastener holes in composite, then joining capability is achieved, but machining-induced micro texture defects are created
Solution Approach 1:
The compliance element is installed beforehand in the fastener, providing cushioning that compensates for the machining-induced micro texture defects in the composite holes. This element absorbs irregularities in hole geometry and surface quality, allowing standard drilling processes to be used while maintaining fastening reliability despite reduced hole quality.
Data Source
Figure 1~2
Figure 3A~3C
Figure 3D~3F
AI summary
A locking member for a fastener, such as a nut (10) or a collar, includes a shank portion (16) and a flanged portion (18), a bore (20) extending the shank portion (16) and the flanged portion (18) and including a first interior portion located within the shank portion (16) and a containment cavity (22) located within the flanged portion (18), and an inner wall (25) defining the containment cavity (22). The containment cavity (22) includes an inner diameter that is greater than an inner diameter of the first interior portion of the bore (20). The inner wall (25) of the containment cavity (22) includes one or a combination of flat/linear surfaces, concave surfaces, and convex surfaces.