Metallized Graphite Fiber Joining for Thermal Mismatch

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Solution Overview

Problem

Graphite fiber materials used in heat exchanger systems face thermal mismatch issues when joined to metallic substrates, are fragile and prone to damage during handling and processing, and have limited thickness due to production capabilities.

Innovation Solution

A method involving the formation of a wetted graphite subassembly with multiple layers of graphite fibers and metallization applied to their ends, secured to a metallic substrate using a braze filler and metallic sheets, allowing for improved thermal matching and increased robustness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If graphite fiber material is joined to metallic substrate, then thermal exchange function is achieved, but thermal mismatch causes structural stress and reliability issues

Engineering Contradiction:

Improvethermal exchange performanceVSAvoidstructural reliability under thermal stress

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

A metallic layer is applied to the ends of graphite fibers to serve as an intermediary between the graphite fiber material and the metallic substrate. This metallic layer acts as a transition zone that accommodates the thermal expansion difference between graphite (0-2 μin/in/°F.) and metal (5-12 μin/in/°F.), reducing structural stress and improving reliability during thermal processing.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention creates a composite structure consisting of graphite fiber material, metallic substrate, and metallic bonding layer. This composite approach combines materials with different thermal expansion coefficients in a controlled manner, allowing each material to contribute its beneficial properties while the metallic layer manages the thermal mismatch.

Inventive Principle:

Principle #40Composite materials

2Strength

If graphite fiber material thickness is increased, then structural robustness is improved, but production capability and handling become more difficult

Engineering Contradiction:

Improvestructural robustnessVSAvoidproduction capability

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The graphite fiber material is divided into multiple layers with metallic material applied to the ends of fibers in each layer. This segmentation allows the structure to achieve increased robustness through layer stacking while maintaining production feasibility by treating each layer as a manageable unit that can be manufactured and assembled separately.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of increasing thickness in a single direction, the invention builds structural robustness by stacking multiple layers in the vertical dimension. Each layer contributes to the overall strength while the layered structure allows for better heat distribution and reduced stress concentrations compared to a monolithic thick structure.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Ease of operation

If graphite fiber material is made thicker, then handling and shaping resistance is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvehandling and shaping easeVSAvoidmanufacturing process complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The metallic material is applied to the ends of graphite fibers during the manufacturing process before final assembly. This preliminary action creates a robust structure that is resistant to handling and shaping damage, while the process is integrated into existing manufacturing capabilities rather than adding separate complex steps.

Inventive Principle:

Principle #10Preliminary action

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 enhances the thermal mismatch performance, increases the structural robustness, and allows for more efficient handling and shaping of graphite fiber materials, enabling the creation of a more durable and efficient heat dissipative structure.

Implementation Method 1

applying a layer of metallization material to ends of the plurality of graphite fibers

Methodology Applied

Scientific EffectMetallization: Physical Vapour Deposition

Implementation Method 2

The braze filler material is heated to a temperature sufficient to melt the filler material and bond the metallic substrate to the metallized graphite fibers

Methodology Applied

Scientific EffectBrazing: Brazing

Data Source

PatentUS8646677B2Method of joining graphite fibers to a substrate

Publication Date: 2014.02.11 HAMILTON SUNDSTRAND SPACE SYST INT INC

AI summary

A method of assembling a metallic-graphite structure includes forming a wetted graphite subassembly by arranging one or more layers of graphite fiber material including a plurality of graphite fibers and applying a layer of metallization material to ends of the plurality of graphite fibers. At least one metallic substrate is secured to the wetted graphite subassembly via the layer of metallization material.