Conductive Adhesive Joints for Lightning Strike Protection

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Solution Overview

Problem

The transition from mechanical fasteners to film adhesive with a non-conductive carrier in aircraft joints creates electrical isolation, potentially leading to structural damage and arcing during lightning strikes, especially in integral fuel tanks, as it disrupts the flow of lightning strike currents.

Innovation Solution

A composite bonded joint is developed using an electrically conductive preform and conductive mesh composition within the adhesive to ensure electrical continuity, where non-conductive surface layers are removed to expose conductive fibers, and a conductive scrim with bonding adhesive and mesh material is applied to facilitate current flow across the bonded joint.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If film adhesive with non-conductive carrier is used to bond composite joints, then weight is reduced and manufacturing is simplified, but electrical continuity is lost leading to lightning strike damage

Engineering Contradiction:

Improvejoint weightVSAvoidlightning strike protection

Core Design Contradiction:

Weight of moving objectVSReliability

Solution Approach 1:

The patent applies composite materials by combining film adhesive with a conductive carrier material that contains conductive particles or fibers. This creates a multi-functional adhesive that provides both bonding and electrical continuity, resolving the contradiction between weight reduction and lightning strike protection.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The conductive carrier material acts as an intermediary between the non-conductive adhesive and the composite structures, providing a conductive pathway for lightning currents while the adhesive provides bonding. This mediator enables both functions to coexist.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If mechanical fasteners are used to join structural components, then electrical continuity for lightning protection is maintained, but weight increases and manufacturing complexity increases

Engineering Contradiction:

Improvelightning strike protectionVSAvoidjoint weight

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent replaces the mechanical fastener system with a chemically bonded adhesive system that incorporates conductive properties. This substitution eliminates the need for holes and fasteners while maintaining electrical continuity through the conductive carrier material.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The adhesive system performs multiple functions simultaneously: structural bonding and electrical conduction. This multi-functionality replaces the separate roles of mechanical fasteners (bonding) and conductive elements (lightning protection).

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Ease of manufacture

If film adhesive with non-conductive carrier is used, then ease of manufacture is improved, but electrical isolation causes arcing and structural damage during lightning strikes

Engineering Contradiction:

Improvebonding process simplicityVSAvoidarcing and structural damage

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The conductive carrier material embedded in the film adhesive creates a composite structure that maintains the ease of adhesive application while adding lightning strike protection capabilities, preventing arcing and structural damage.

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

This solution effectively prevents fuel vapor ignition and maintains structural integrity during severe lightning strikes by ensuring that lightning strike currents can flow safely through the bonded joints, demonstrating applicability beyond aerospace to any composite structures sensitive to lightning strikes.

Implementation Method 1

The mesh composition includes a conductive mesh material and conductive particles dispersed throughout a matrix material. The conductive mesh material and conductive particles provide pathways for electrical conduction, ensuring that lightning strike currents can flow through the bonded joint.

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

The mesh composition includes an adhesive that bonds the conductive mesh material and conductive particles to the composite structures.

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS11575220B1Process for constructing lightning strike protection for adhesively bonded graphite composite joints

Publication Date: 2023.02.07 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

A bonded joint for use in bonding composite materials is provided and includes a composite rib having electrically conductive properties and a composite structure having electrically conductive properties. An electrically conductive preform is provided that facilitates a bond between the composite rib and the composite structure. A mesh composition that bonds the composite rib to the preform and that bonds the preform to the composite structure is provided and is electrically conductive to conduct current between the composite rib and the composite structure.