CMC Liner Attachment Structure for Thermal Expansion Mismatch

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Solution Overview

Problem

The mismatch in thermal expansion coefficients between ceramic matrix composite (CMC) exhaust liners and metal exhaust ducts in aircraft engines leads to stress and displacement, causing potential failure and deterioration.

Innovation Solution

An attachment apparatus is used to securely attach CMC liners to metal ducts, featuring a mounting plate, backer plate, and fasteners with thermal spacers to accommodate thermal expansion, preventing fastener heads from being pulled through the liner and ensuring even load distribution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If CMC liners are directly attached to metal ducts, then the attachment is simple, but thermal expansion mismatch causes stress and displacement leading to failure

Engineering Contradiction:

Improveattachment structureVSAvoidattachment reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A backer plate is introduced as an intermediary component between the CMC liner and metal duct. The backer plate accommodates thermal expansion differences by allowing the CMC liner to expand against it while remaining attached to the metal duct, preventing fastener pull-through and reducing stress concentrations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The attachment system transitions from a direct 1D fastener connection to a 2D distributed attachment system using a backer plate with multiple fasteners arranged in a pattern, spreading the thermal stress across a larger area and preventing localized failure.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If thermal spacers and backer plates are used to accommodate thermal expansion, then attachment reliability improves, but device complexity increases

Engineering Contradiction:

Improveattachment reliabilityVSAvoidattachment structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system changes the physical parameters of the attachment by introducing thermal spacers with specific thermal expansion properties and backer plates with optimized geometry, allowing the attachment to adapt to thermal conditions while maintaining structural integrity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The backer plate and thermal spacers are pre-installed on the metal duct before CMC liner installation, establishing a compliant attachment structure that is ready to accommodate thermal expansion from the outset, preventing installation damage and ensuring reliable operation.

Inventive Principle:

Principle #10Preliminary action

3Strength

If fasteners are used to securely attach CMC liners, then attachment strength improves, but thermal expansion causes fastener heads to be pulled through the liner

Engineering Contradiction:

Improveattachment strengthVSAvoidfastener pull-through

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The backer plate serves as a cushioning element positioned behind the CMC liner, absorbing the expansion forces before they can transfer to the fastener heads. This prevents fastener pull-through by providing a compliant backing that accommodates thermal movement.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The backer plate acts as an intermediary between the expanding CMC liner and the fasteners, intercepting the thermal expansion forces and preventing them from acting directly on the fastener heads, thereby eliminating the pull-through mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 apparatus provides a secure and durable attachment that withstands high temperatures, reducing the risk of failure and maintaining the integrity of the CMC liner and metal duct, while being cost-effective and easy to install.

Implementation Method 1

mismatch in thermal expansion coefficients between ceramic matrix composite (CMC) exhaust liners and metal exhaust ducts

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS12398660B2Systems and methods for attachment of materials having different thermal expansion coefficients

Publication Date: 2025.08.26 GENERAL ELECTRIC CO

AI summary

An apparatus for attaching two components having different coefficients of thermal expansion includes a mounting member configured to be movably coupled relative to a first component, an attachment member opposite the mounting member and configured to be attached to a second component, and at least one support post interconnecting the mounting member and the attachment member. The apparatus also includes a backer plate including at least one aperture configured to permit at least one fastener to pass therethrough and pass through the second component and through at least one aperture in the attachment member to secure the backer plate and the attachment member to the second component and to attach the second component to the first component. The diameter of the aperture of the backer plate restricts the head of the fastener from passing through the aperture of the backer plate.