CMC Fastening System Using Compliant Metal Bracket

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Solution Overview

Problem

Conventional fastening systems for ceramic matrix composites (CMCs) to metallic engine components face challenges such as stress concentrations, space constraints, and inability to withstand extreme loads and thermal expansion mismatches, leading to potential fracture and degradation.

Innovation Solution

A CMC fastening system featuring a slotted, detachable metal bracket with flared end rivets or pins, and optional sleeves and leaf springs to minimize stress and accommodate thermal expansion differences, along with Belleville washers for additional flexibility and load distribution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If traditional screw and rivet fastening systems are used to attach CMCs to metallic components, then the fastening system can provide mechanical connection, but it creates stress concentrations and increases the likelihood of CMC fracture

Engineering Contradiction:

Improvefastening connection strengthVSAvoidCMC fracture resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent introduces a compliant bracket as an intermediary component between the CMC and metallic engine components. This bracket acts as a mediator that distributes fastening loads across a broader area, reducing stress concentrations at individual fastener points and thereby decreasing the likelihood of CMC fracture while maintaining mechanical connection strength

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The compliant bracket is designed with specific material properties and geometric features (such as curved surfaces and varying thickness) that change the mechanical parameters of the fastening system. These parameter changes allow the bracket to deform elastically under load, redistributing stresses away from the CMC and improving fracture resistance

Inventive Principle:

Principle #35Parameter changes

2Reliability

If CMC self-sealing approach is used where oxygen is consumed in CMC microcracks, then damage tolerance is improved, but the system cannot sustain heavy loads and high temperatures during engine assembly

Engineering Contradiction:

Improvedamage toleranceVSAvoidload bearing capacity

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent combines two approaches: the CMC self-sealing mechanism for damage tolerance and the compliant bracket fastening system for load bearing capacity. The bracket system provides the mechanical strength needed during assembly and operation, while the self-sealing CMC provides damage tolerance, creating a hybrid solution that achieves both objectives simultaneously

Inventive Principle:

Principle #5Merging (Combining)

3Strength

If rigid fastening systems are used to attach CMCs, then mechanical connection is achieved, but thermal expansion mismatch between CMC and metal causes stress and potential failure

Engineering Contradiction:

Improvemechanical connection strengthVSAvoidthermal expansion stress

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The compliant bracket is specifically designed to accommodate thermal expansion differences between CMC and metallic components. The bracket's compliant geometry allows it to expand and contract differently than the rigid CMC or metal parts, absorbing thermal stresses and preventing failure due to thermal expansion mismatch while maintaining mechanical connection

Inventive Principle:

Principle #37Thermal expansion

4Strength

If conventional fastening systems are used, then CMCs can be attached to engine components, but space constraints are created on the rest of the engine system

Engineering Contradiction:

Improvefastening capabilityVSAvoidengine system space

Core Design Contradiction:

StrengthVSVolume of moving object

Solution Approach 1:

The compliant bracket introduces dynamic flexibility to the fastening system, allowing the bracket to deform and adapt to space constraints within the engine assembly. This dynamic capability enables the fastening system to maintain connection strength while accommodating limited space availability, unlike rigid fastening systems that require fixed geometric clearances

Inventive Principle:

Principle #15Dynamics

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 system effectively reduces stress concentrations, accommodates thermal expansion, and sustains extreme loads, enhancing durability and vibration damping while maintaining structural integrity under harsh engine conditions.

Implementation Method 1

a leaf spring inserted between the bracket and the CMC to dampen vibrations

Methodology Applied

Scientific EffectVibration damping: Damping

Implementation Method 2

Belleville washers for additional flexibility and load distribution

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentEP1923578B1CMC fastening system

Publication Date: 2017.01.18 UNITED TECH CORP

AI summary

A simple ceramic matrix composite fastening system that is utilized for attaching components of dissimilar materials, particularly, ceramic matrix composites (CMCs) (18) and metallic engine components. The system is comprised of a detachable subassembly bracket (14) fabricated from metal. The bracket (14) has a metallic engine component (12) attached to one end and a CMC component (18) attached to the other end. The bracket (14) releasably secures the CMC (18) and the metallic component (12) together using rivets or pins (26), which are inserted into holes (20) through the CMC (18) to securely fasten the adjoining parts.