Coated Fastener Seal for Lightning-Safe Composite Joints
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Solution Overview
Problem
Composite aircraft structures face challenges with lightning protection due to the high resistance of carbon fibers and epoxy, leading to potential ignition and arcing issues at fastener interfaces, as drilling creates machining-induced defects and gaps that hinder intimate contact between fasteners and composite materials, making them susceptible to lightning strikes.
Innovation Solution
A fastener design featuring a coated pin member with a conforming conical seal and textured surface, which includes a metallic coating for improved electrical conductivity and a seal element made of copper, allowing for intimate contact with the composite structure and reducing contact resistance, thereby minimizing arcing and plasma formation during lightning strikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fastener is used with composite structures, then mechanical fastening is achieved, but electrical contact and lightning protection deteriorate due to high resistance of carbon fibers and epoxy
Solution Approach 1:
The patent introduces a conductive coating layer as an intermediary between the fastener and the composite structure. This coating layer, made of electrically conductive material, mediates the electrical contact between the fastener and the high-resistance composite structure, enabling effective lightning current dissipation while maintaining mechanical fastening function.
Solution Approach 2:
The patent changes the electrical conductivity parameter of the fastener interface by applying a conductive coating. This modifies the electrical properties of the contact surface, transforming the high-resistance interface into a low-resistance path for electrical current, thereby improving lightning protection without altering the mechanical fastening capability.
2Ease of manufacture
If drilling is performed on composite structures, then fastener holes are created, but machining-induced defects and gaps increase contact resistance
Solution Approach 1:
The conductive coating acts as an intermediary that bridges the gaps and defects created during drilling. Rather than requiring perfect hole surfaces, the coating fills and conforms to the irregularities, creating continuous electrical contact paths that overcome the discontinuities introduced by machining-induced defects.
Solution Approach 2:
The patent changes the surface properties of the fastener by applying a conductive coating, which alters the electrical contact characteristics. This coating compensates for the poor surface quality created by drilling, transforming the high-resistance rough surface into a conductive interface that maintains low electrical resistance despite manufacturing imperfections.
3Reliability
If a coated fastener is used, then electrical conductivity is improved, but coating application complexity increases
Solution Approach 1:
The patent applies a conductive coating to the fastener surface, changing the electrical conductivity parameter of the fastener interface. This simple parameter change—adding a conductive layer—significantly improves electrical contact and lightning protection without requiring complex design modifications to the fastener structure itself.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The coated and textured fastener improves electrical contact, reduces the likelihood of arcing, and enhances mechanical interlocking, effectively managing lightning strikes by ensuring efficient current dissipation and minimizing damage to aircraft structures.
Implementation Method 1
a coated pin member with a conforming conical seal and textured surface, which includes a metallic coating for improved electrical conductivity
Implementation Method 2
a seal element made of copper, allowing for intimate contact with the composite structure and reducing contact resistance
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A pin member (12) for a fastener includes an elongated shank having a first end, a second end opposite the first end, a cylindrical shank portion having an outer surface, a head located at the first end of the elongated shank, the head including a bearing surface located on the bearing surface of the head, and a threaded portion located at the second end of the elongated shank. The pin member can be fully coated with a coating. A conformable seal element (24) is attached to the pin member, which is adapted to fill the microscopic voids between the bearing surface of the head of the pin member and the surrounding structure under the axial load exerted by the fastener during installation. The seal element can be separate and distinct from the pin member. The seal element can be attached to the pin member for the sake of convenience, but the seal element can deform independently of the pin member and the surrounding structure in response to the forces exerted by the fastener.