Conforming Seal Fasteners for Composite Lightning Protection
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Solution Overview
Problem
Composite aircraft structures face challenges with drilling-induced defects and poor electrical conductivity, leading to lightning strikes and fuel vapor ignition risks due to machining-induced micro texture and inadequate fastener-composite contact.
Innovation Solution
A fastener with a coated and textured pin member, featuring a metallic coating and a conforming conical seal, which improves electrical conductivity and intimate contact with the composite structure, reducing arcing and plasma formation during lightning strikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sleeved fastener is used to achieve intimate contact with the composite hole, then electrical conductivity is improved, but machining-induced micro texture prevents complete contact and increases complexity
Solution Approach 1:
A conforming conical seal element is introduced as an intermediary between the fastener and the composite structure. The seal conforms to the machining-induced micro texture and provides a continuous electrical contact path, mediating the interface between the fastener and the textured composite surface without requiring complex sleeved fastener designs
Solution Approach 2:
The seal element changes the electrical contact parameters by providing a conforming surface that adapts to the micro texture. The conical geometry and material properties of the seal are optimized to ensure intimate contact and electrical conductivity despite the textured composite surface
2Ease of manufacture
If drilling is performed to create fastener holes in composite, then joining capability is improved, but machining-induced micro texture and defects are created
Solution Approach 1:
The conforming conical seal element converts the harmful machining-induced micro texture into a beneficial feature by conforming to the texture and creating intimate contact. The seal's conical geometry allows it to adapt to the textured surface, transforming the defect into a contact-enhancing feature
Solution Approach 2:
The seal element acts as a flexible conforming layer that adapts to the irregularities of the drilled hole surface. This thin film approach allows the seal to conform to the machining-induced micro texture while maintaining electrical and mechanical contact
3Weight of moving object
If carbon fibers and epoxy are used in composite structures, then light weight and strength are improved, but electrical conductivity deteriorates
Solution Approach 1:
The solution uses a composite approach by combining the lightweight carbon fiber/epoxy structure with a conductive seal element. The seal material is selected to provide electrical conductivity while maintaining compatibility with the composite structure, creating a hybrid system that addresses both weight and conductivity requirements
Solution Approach 2:
The conforming seal serves as an intermediary that bridges the electrical conductivity gap between the non-conductive composite and the fastener. This mediator layer provides the necessary electrical path without compromising the lightweight composite structure
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 solution enhances electrical contact and mechanical interlocking, minimizing arcing and plasma formation, while effectively dissipating lightning currents and reducing the risk of fuel vapor ignition.
Implementation Method 1
the pin member is adapted to improve electrical contact between the head and the composite structure
Implementation Method 2
a conforming conical seal, which improves electrical conductivity and intimate contact with the composite structure
Data Source
AI summary
A pin member 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 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.