Insulated Blind Fastener Assembly for Lightning Arc Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Aircraft composite structures are prone to electrical arcing with metal fasteners during lightning strikes, which can ignite fuel in fuel tanks, posing a risk due to the conductive differences between composite and metal materials.
Innovation Solution
A blind fastener design featuring a bolt part, a sleeve part, and a tubular insulating sheath that moves into a post-installation configuration where the sheath covers the interface between the sleeve and the structure, preventing direct contact and arcing, thus ensuring an intact insulating barrier without the need for additional coatings or inspections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal fasteners are used to fasten composite structures, then fastening strength is achieved, but electrical arcing occurs during lightning strikes due to conductive differences between composite and metal materials
Solution Approach 1:
An insulating sleeve is introduced as an intermediary component between the metal blind fastener and the composite structure. This sleeve prevents direct electrical contact between the conductive fastener and the composite material, thereby eliminating the arcing pathway while maintaining the mechanical fastening function. The sleeve is specifically positioned at the interface where arcing would occur during lightning strikes.
Solution Approach 2:
The solution employs a composite fastening system combining metal (conductive) and insulating materials. The metal blind fastener provides mechanical strength and fastening capability, while the insulating sleeve provides electrical isolation. This composite approach allows both the conductive and insulating properties to coexist in a single fastening assembly, resolving the contradiction between mechanical performance and electrical safety.
2Object-affected harmful factors
If insulating coatings are applied to prevent arcing, then electrical insulation is improved, but additional manufacturing steps and quality inspections are required
Solution Approach 1:
The insulating function and mechanical fastening function are merged into a single integrated assembly. The insulating sleeve is designed to be installed concurrently with the blind fastener during the same manufacturing operation, eliminating the need for separate coating application and inspection steps. The sleeve's internal geometry is designed to engage with the fastener body, creating a unified component system.
Solution Approach 2:
The insulating sleeve is designed with self-retention features that allow it to automatically secure itself to the blind fastener during installation. The sleeve's internal structure engages with the fastener body through interference fits or mechanical interlocking, eliminating the need for additional bonding agents, clips, or fastening steps. This self-service mechanism reduces manufacturing complexity while ensuring reliable insulation.
3Reliability
If the insulating sheath is made elastically or plastically deformable, then it can accommodate installation variations and maintain contact, but the material selection and design complexity increase
Solution Approach 1:
The insulating sleeve is designed with deformable characteristics that allow it to dynamically adapt to variations in installation conditions. During installation, the sleeve can elastically or plastically deform to accommodate slight misalignments or dimensional tolerances of the composite structure holes. This dynamic behavior ensures continuous contact and maintained insulation integrity without requiring precision manufacturing or complex adjustment mechanisms.
Data Source
AI summary
A blind fastener is disclosed having a bolt part, a sleeve part, and a tubular insulating sheath. The bolt part is at least partially received within the sleeve part. A first end of the sheath is retained on the bolt part such that relative axial movement between the first end of the sheath and the bolt part is substantially prevented. The blind fastener is movable between: a pre-installation configuration in which the sleeve part has a first axial position relative to the bolt part and a predetermined section of the sheath is adjacent an outer surface of the sleeve part; and a post-installation configuration in which the sleeve part has a second, different axial position relative to the bolt part and the predetermined section of the sheath is adjacent an inner surface of the sleeve part.