Conductive Fastener Coating for CFRP FSDA Lightning Protection

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Solution Overview

Problem

Conventional assembly and fastening processes for aircraft structures made from lightweight composite materials like carbon fiber reinforced plastic (CFRP) are time-consuming and costly, and full-size determinant assembly (FSDA) poses challenges in providing sufficient electromagnetic effects (EME) protection due to misaligned holes and uneven hole sidewalls, which limit current pathways during lightning strikes.

Innovation Solution

A conductively coated fastening system is introduced, where electrically conductive gap fillers are applied to the sidewalls of pre-formed holes in CFRP structural elements and fasteners are coated with an electrically conductive material, enhancing current pathways and ensuring EME protection, allowing for the use of FSDA without sacrificing safety.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If FSDA is used to reduce production time and cost, then assembly efficiency is improved, but electromagnetic effects (EME) protection is worsened due to misaligned holes and limited current pathways

Engineering Contradiction:

Improveassembly efficiencyVSAvoidEME protection

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

An electrically conductive gap filler material is introduced as an intermediary substance between the fastener and the CFRP structural elements. This gap filler compensates for misaligned holes by filling the voids and creating continuous electrical pathways, thereby maintaining EME protection while allowing FSDA misalignment to persist

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electrical conductivity parameter of the assembly is enhanced by applying electrically conductive coatings to both the fastener surface and the hole sidewalls. This parameter change ensures sufficient current pathways for lightning protection even when geometric alignment is imperfect

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional assembly processes are used to ensure proper alignment and EME protection, then EME protection is improved, but production time and cost increase

Engineering Contradiction:

ImproveEME protectionVSAvoidproduction time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

Holes are pre-formed in each structural element separately before assembly, and electrically conductive coatings are applied to the hole sidewalls in advance. This preliminary action eliminates the need for repeated stacking and alignment operations, reducing production time while ensuring EME protection is already in place before final assembly

Inventive Principle:

Principle #10Preliminary action

3Productivity

If FSDA is used with separately pre-formed holes, then production efficiency is improved, but hole alignment deteriorates limiting contact between CFRP and fastener

Engineering Contradiction:

Improveproduction efficiencyVSAvoidhole alignment

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The electrically conductive gap filler acts as a mediator that bridges the gap caused by misaligned holes. It fills the voids between the fastener and CFRP surfaces, ensuring adequate contact area and electrical connectivity despite the lack of precise hole alignment inherent in FSDA

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

An electrically conductive composite coating is applied to the fastener surface, combining mechanical fastening functionality with electrical conductivity. This composite material ensures both structural integrity and continuous electrical pathways even with imperfect hole alignment

Inventive Principle:

Principle #40Composite materials

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 conductively coated fastening system reduces production time and costs by enabling efficient assembly of CFRP structures while providing effective EME protection, even in misaligned conditions, ensuring safety and performance during lightning strikes.

Implementation Method 1

The shank is configured to be inserted into the first hole and the second hole. In some examples, the fastener comprises an electrically conductive coating... at least a portion of the first hole and second hole do not align... electrically conductive gap filler applied to a first structural element sidewall of the first hole

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentEP3848593B1Conductively coated fastening systems for full size determinant assembly (FSDA)

Publication Date: 2023.08.30 THE BOEING CO

Figure 1
Figure 2
Figure 3A~3C

AI summary

Conductively coated fastening systems are disclosed herein. An apparatus (8) includes a fastening system (10) and a structural assembly (12). The structural assembly (12) comprises a first structural element (16) made of an electrically conductive fiber reinforced plastic and a second structural element (18). The first structural element (16) comprises a first hole (48) and the second structural element comprises a second hole (50). The first and second holes (48,50) are separately pre-formed prior to assembly of the structural assembly (12). The structural assembly (12) further comprises an electrically conductive gap filler (24) applied to a first structural element sidewall (22) of the first hole (48) of the first structural element (26). The fastening system (10) comprises a fastener (30) comprising a head (38) and a shank (40) extending from the head (38). The shank (40) is configured to be inserted into the first hole (48) and the second hole (50).