Blind Fastener Insulation Layout for Lightning Arc Prevention
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Solution Overview
Problem
Aircraft composite structures are susceptible to electrical arcing during lightning strikes, which can ignite fuel in fuel tanks due to the conductive properties of metal fasteners, posing a risk to safety.
Innovation Solution
A blind fastener system comprising a sleeve member that deforms during installation, incorporating an electrically insulating member to ensure a robust and intact insulating barrier between the fastener and structure, preventing arcing by maintaining the insulating member's integrity and eliminating the need for additional coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal fasteners are used to fasten composite structures, then mechanical strength and structural integrity are improved, but electrical conductivity increases causing arcing during lightning strikes
Solution Approach 1:
An electrically insulating member is introduced as an intermediary between the metal fastener and the composite structure. This insulating member prevents direct electrical contact while allowing mechanical fastening, thereby eliminating the arcing pathway during lightning strikes while maintaining structural integrity.
Solution Approach 2:
The fastener system uses a composite construction combining metal components (bolt, sleeve) with an electrically insulating material. This composite approach allows the metal to provide mechanical strength while the insulating material prevents electrical conduction, resolving the contradiction between mechanical and electrical properties.
2Object-affected harmful factors
If insulating coatings are applied to metal fasteners, then electrical insulation is improved, but manufacturing complexity and inspection requirements increase
Solution Approach 1:
The electrically insulating member is pre-installed onto the metal fastener during the fastening operation itself, rather than requiring separate coating applications. This preliminary action integrates insulation into the primary installation process, eliminating additional manufacturing steps and post-installation inspection requirements.
Solution Approach 2:
The insulating member is designed to be self-contained and self-positioning on the fastener. The fastener system serves its own insulation needs through this integrated component, eliminating the need for external coating processes and subsequent quality inspection of coating integrity.
3Object-affected harmful factors
If the insulating member covers the entire outer surface of the sleeve, then electrical insulation is maximized, but mechanical interference fit and structural bonding are reduced
Solution Approach 1:
The insulating member is positioned to cover only specific portions of the sleeve's outer surface - specifically the regions that contact the composite structure. By applying insulation locally rather than uniformly, the design maintains electrical insulation where needed while preserving metal-to-metal contact areas for structural bonding and interference fit.
Solution Approach 2:
The outer surface of the sleeve is segmented into distinct functional zones: insulated regions for electrical protection and non-insulated regions for mechanical bonding. This segmentation allows simultaneous achievement of electrical insulation and structural strength through differentiated surface treatment.
Data Source
Figure 1a~2b
Figure 3a~4
Figure 5
AI summary
There is provided a blind fastener configured to be installed in a bore of a given length. The blind fastener comprises a sleeve member configured to deform during installation of the blind fastener; a bolt member at least partially received within the sleeve member; and an insulating member fixedly disposed on the sleeve member. The sleeve member has a predefined outer surface region that is arranged to be disposed within the bore after installation of the blind fastener. The insulating member and the sleeve member are mutually configured such that the insulating member is present on a first sub-region of the predefined outer surface region and is not present on a second sub-region of the predefined outer surface region. Each of the first and second sub-regions comprises a complete circumference of the sleeve member.