Compliant Metallic-Composite Joint Interface

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Solution Overview

Problem

Joining metallic and composite materials is challenging due to thermal expansion mismatch and galvanic corrosion, as existing techniques like pi-shaped joints are not effective in forming reliable interfaces between these dissimilar materials.

Innovation Solution

A system that uses a pi-shaped composite preform with an inert compliant layer, such as titanium, between the metallic and composite members to act as a barrier against galvanic corrosion and match thermal expansion coefficients, ensuring a compliant and non-corrosive interface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a pi-shaped composite preform is used to join metallic and composite materials, then the structural connection is achieved, but thermal expansion mismatch causes separation and failure at the interface

Engineering Contradiction:

Improvejoint strengthVSAvoidinterface reliability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

An inert compliant layer is introduced as an intermediary between the metallic member and the composite preform. This layer has a coefficient of thermal expansion intermediate between the metal and composite, acting as a buffer that accommodates differential thermal expansion while maintaining the structural connection and preventing interface separation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The compliant layer is designed with specific material parameters - particularly a coefficient of thermal expansion that falls between those of the metallic and composite materials. This parameter selection allows the layer to absorb thermal stresses through elastic deformation, maintaining joint integrity across temperature variations.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If dissimilar metallic and composite materials are joined directly, then structural assembly is achieved, but galvanic corrosion occurs at the interface

Engineering Contradiction:

Improveassembly easeVSAvoidgalvanic corrosion

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The inert compliant layer serves as a galvanic isolation barrier between the metallic member and composite preform. Being electrically non-conductive, it breaks the electrical circuit required for galvanic corrosion while still providing mechanical connection, thus preventing corrosion without complicating the assembly process.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The compliant layer creates an inert, non-conductive environment between the dissimilar materials, preventing the electrochemical reactions that cause galvanic corrosion. This inert barrier eliminates the harmful interaction while maintaining the structural joint.

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

3Reliability

If an inert compliant layer is added between metallic and composite members, then thermal expansion mismatch and galvanic corrosion are mitigated, but the device complexity increases

Engineering Contradiction:

Improveinterface reliabilityVSAvoidjoint complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The compliant layer is implemented as a thin film or coating applied to the metallic member, rather than a bulky component. This thin-film approach provides the necessary thermal and galvanic protection while adding minimal complexity to the joint assembly, maintaining ease of manufacture.

Inventive Principle:

Principle #30Flexible shells and thin films

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 solution effectively reduces the risk of galvanic corrosion and thermal stress separation by using a compliant layer that matches the thermal expansion of the composite material, creating a durable and corrosion-resistant joint between metallic and composite materials.

Implementation Method 1

the compliant layer has a coefficient of thermal expansion that more closely matches that of the preform to reduce the risk of separation therebetween when subjected to thermal stresses

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the compliant layer primarily acts as a ductile layer to absorb the greater expansion of the metal against the lesser expansion of the composite as thermal energy is applied

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 3

the compliant layer acts as a barrier to galvanic corrosion that might otherwise occur between the carbon in the preform and the metallic member

Methodology Applied

Scientific EffectGalvanic corrosion prevention:

Data Source

PatentUS7611595B2System, method, and apparatus for metallic-composite joint with compliant, non-corrosive interface

Publication Date: 2009.11.03 LOCKHEED MARTIN CORP

AI summary

A metallic-composite joint is formed by inserting a metallic member into a slot of a pi-shaped composite preform. The preform is formed from woven carbon fiber in a binder of resin and may or may not be cured prior to assembly. An inert compliant layer is located between the legs of the preform and the metallic member. The resin binder or an adhesive is used to bond the compliant layer to the preform. The compliant layer has a coefficient of thermal expansion that more closely matches that of the preform. The properties of the compliant layer also avoid galvanic corrosion between the carbon in the preform and the metallic member.