Injectable Fastener Cap With Annular Seal for Lightning Strike Containment
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Solution Overview
Problem
Existing fastener caps fail to provide effective spark suppression and fuel leakage prevention during lightning strikes due to inadequate sealing and bonding capabilities, particularly in composite and metallic structures.
Innovation Solution
A cap design featuring an inner and outer cap member with an annular sealing cavity, a sealing material inlet for injecting curable sealing material, and a flow restriction feature to ensure a strong, reliable bond and seal, using materials like epoxy-based adhesives for rapid curing and enhanced shock resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sealing material is applied before cap positioning, then the seal is established early, but the handling and curing time is excessive and the material may start to cure before application
Solution Approach 1:
The cap is pre-assembled and positioned on the fastener before sealing material application. The sealing material is then injected into the pre-formed sealing cavity, allowing the material to be applied at the optimal moment rather than beforehand. This eliminates waiting time and ensures the material is applied during its working life.
2Productivity
If sealing material is injected after cap positioning, then the material is applied during its working life with quick cure, but the sealing cavity must be precisely formed beforehand
Solution Approach 1:
The cap is divided into inner and outer cap members that are assembled together to form the sealing cavity. This segmentation allows the cavity to be pre-formed with precise dimensions through modular assembly, while enabling post-positioning sealing material injection for quick cure application.
3Ease of manufacture
If air gaps are present in the sealing material, then the application process is simpler, but the seal is compromised and fuel leakage occurs
Solution Approach 1:
Sealing material is injected under pressure into the sealing cavity through an injection device. This hydraulic/pneumatic injection method ensures the material flows uniformly, fills the entire cavity, and eliminates air gaps, creating a complete seal without compromising application simplicity.
4Strength
If the cap provides strong bond and shock resistance, then the seal withstands accidental knocks, but the cap structure becomes more complex
Solution Approach 1:
The cap combines inner and outer cap members made of different materials with complementary properties. The inner cap member provides sealing surface precision, while the outer cap member provides structural strength and shock resistance. This composite structure achieves high strength without excessive complexity.
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 cap design provides a stable, quick-curing seal that withstands accidental knocks and minimizes fuel leakage, effectively containing out-gassing and sparking events during lightning strikes, while ensuring a strong bond between the cap and structure.
Implementation Method 1
a flow of curable sealing material from the sealing material inlet into the annular sealing cavity
Data Source
AI summary
The present invention proposes a cap for forming a sealed cavity around one end of a fastener to thereby contain out-gassing and sparking events in the event of a lightning strike to the fastener. The invention also proposes a joint comprising such a cap, and a kit of parts and method for installing such a cap. A cap according to the invention comprises: an inner cap member having an annular base terminating at an edge which surrounds an opening into an air cavity for enclosing the one end of a fastener; and an outer cap member having an annular skirt or flange which extends radially outwardly away from the annular base, the annular skirt or flange and annular base between them defining an annular sealing cavity. The cap also comprises a sealing material inlet comprising an opening in the outer cap member that is in fluid communication with the annular sealing cavity, the opening being arranged to interconnect with a sealing material injection device to provide a flow of curable sealing material from the sealing material inlet into the annular sealing cavity.