Engine Bi-Material Joint with Interface Flange for Thermal Fit

Solution Overview

Problem

Thermal stresses at the joints of engine casing components due to thermal gradients cause loosening and reduced fit, leading to potential loosening of joints.

Innovation Solution

A bi-material joint design using Titanium for the generator case flange and Inconel 718 for the TSC flange, with an interface flange made of the same material as the generator case flange to maintain a tight fit and counter thermal expansion, ensuring structural integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a single-material joint is used between generator case flange and TSC flange, then manufacturing is simpler, but thermal expansion mismatch causes joint loosening under thermal stress

Engineering Contradiction:

Improvejoint manufacturing simplicityVSAvoidjoint fit stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The joint employs a bi-material construction where the generator case flange is made of titanium and the TSC flange is made of Inconel 718. This composite material approach allows each material to be selected for its optimal properties: titanium for the generator case (lower thermal expansion) and Inconel 718 for the TSC (higher thermal expansion resistance), thereby maintaining joint integrity under thermal stress while accounting for the complexity of working with different materials

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention changes the material parameter (thermal expansion coefficient) by selecting two different materials with complementary properties. The titanium generator case flange has a lower coefficient of thermal expansion while the Inconel 718 TSC flange has a higher coefficient, creating a balanced system where thermal expansion differences are managed to prevent joint loosening

Inventive Principle:

Principle #35Parameter changes

2Reliability

If different materials are used for generator case flange and TSC flange, then thermal expansion mismatch is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improvejoint fit stabilityVSAvoidjoint structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The joint employs a bi-material construction where the generator case flange is made of titanium and the TSC flange is made of Inconel 718. This composite material approach allows each material to be selected for its optimal properties: titanium for the generator case (lower thermal expansion) and Inconel 718 for the TSC (higher thermal expansion resistance), thereby maintaining joint integrity under thermal stress while accounting for the complexity of working with different materials

Inventive Principle:

Principle #40Composite materials

3Device complexity

If thermal expansion is not compensated, then joint structure remains simple, but thermal stresses cause joint loosening and premature wear

Engineering Contradiction:

Improvejoint structure simplicityVSAvoidjoint fit stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The invention changes the material parameter (thermal expansion coefficient) by selecting two different materials with complementary properties. The titanium generator case flange has a lower coefficient of thermal expansion while the Inconel 718 TSC flange has a higher coefficient, creating a balanced system where thermal expansion differences are managed to prevent joint loosening

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The joint employs a bi-material construction where the generator case flange is made of titanium and the TSC flange is made of Inconel 718. This composite material approach allows each material to be selected for its optimal properties: titanium for the generator case (lower thermal expansion) and Inconel 718 for the TSC (higher thermal expansion resistance), thereby maintaining joint integrity under thermal stress

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

The bi-material joint effectively maintains a secure fit and reduces vibrations by matching thermal expansion coefficients, preventing premature wear and unscheduled maintenance.

Implementation Method 1

the interface flange exerting a radially inward force on part of the generator case flange upon the interface flange undergoing thermal expansion

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the third coefficient of thermal expansion of the interface flange is equal to the first coefficient of thermal expansion of the generator case flange

Methodology Applied

Scientific EffectThermal expansion coefficient matching: Thermal Expansion

Data Source

PatentEP4098858B1BI-material joint for engine

Publication Date: 2025.08.20 PRATT & WHITNEY CANADA CORP

Figure 1~2
Figure 3~4

AI summary

An engine bi-material joint (50) includes a first flange (48) composed of a first material defining a first coefficient of thermal expansion, and a second flange (38) composed of a second material defining a second coefficient of thermal expansion. The second material is different from the first material. An interface flange (58) is engaged with the first flange (48) and with the second flange (38). The interface flange (58) material defines a third coefficient of thermal expansion being equal to or less than the first coefficient of thermal expansion and less than the second coefficient of thermal expansion. The first coefficient of thermal expansion is less than the second coefficient of thermal expansion.