CMC-Metal Joint Using Spring-Loaded Keys
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Solution Overview
Problem
Robustly and efficiently attaching ceramic matrix composite (CMC) materials to metals in gas turbine engines is challenging due to thermal stress arising from the mismatch of coefficients of thermal expansion between CMCs and metal support structures.
Innovation Solution
A joint system using ceramic keys and recesses, where the keys are spring-loaded and biased into engagement with the recesses on the CMC surface, resisting axial separation and accommodating differential thermal expansion through compliant mounting and hoop stress, while maintaining a gap to prevent chemical reaction and allow cooling air passage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If CMC materials are attached to metal support structures using rigid joints, then structural strength is improved, but thermal stress increases due to mismatch of coefficients of thermal expansion
Solution Approach 1:
The patent changes the mechanical properties of the joint by introducing spring-loaded keys that can deflect, transforming the joint from rigid to compliant. This allows the joint to accommodate thermal expansion differences while maintaining structural integrity, resolving the contradiction between strength and thermal stress.
Solution Approach 2:
The joint incorporates movable spring-loaded keys that can dynamically adjust their position in response to thermal expansion forces. This dynamic capability allows the joint to maintain strength while accommodating dimensional changes, preventing thermal stress accumulation.
2Stress or pressure
If CMC materials are attached to metal support structures using compliant mounting, then thermal stress is reduced, but attachment robustness deteriorates
Solution Approach 1:
The joint divides the attachment function into multiple elements: spring-loaded keys for compliance, recesses for positioning, and interference fits for retention. This segmentation allows each element to perform its specific function optimally, achieving both compliance and robustness simultaneously.
Solution Approach 2:
The joint uses a composite approach combining metallic keys with CMC recesses, leveraging the strengths of both materials. The metallic keys provide compliance and strength, while the CMC recesses provide thermal stability and geometric precision, achieving both compliance and robustness.
3Device complexity
If CMC and metal components are placed in direct contact, then structural simplicity is improved, but chemical reaction between materials occurs at high temperature
Solution Approach 1:
The spring-loaded keys act as intermediary elements between the CMC and metal support structure, preventing direct contact and potential chemical reactions. The keys transmit mechanical loads while maintaining physical separation, eliminating the harmful chemical interaction.
4Strength
If CMC and metal components are tightly fitted, then attachment strength is improved, but relative movement during thermal expansion is restricted
Solution Approach 1:
The joint uses dynamic spring-loaded keys that can deflect under load, allowing the joint to maintain strength while accommodating thermal expansion. The keys provide both mechanical retention and compliance, enabling relative movement without compromising attachment strength.
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 joint system effectively resists thermal stresses and maintains structural integrity by allowing relative movement between CMC and metal components, ensuring reliable attachment and operation in high-temperature environments.
Implementation Method 1
the keys are spring-loaded and biased into engagement with the recesses on the CMC surface
Implementation Method 2
resisting axial separation and accommodating differential thermal expansion through compliant mounting and hoop stress
Implementation Method 3
maintaining a gap to prevent chemical reaction and allow cooling air passage
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A first member (28) is retained to a second member (32) to resist separation in a first direction (106). A joint comprises a first recess (102) in the first member (28). The first member (28) comprises at least a ceramic matrix composite (CMC) substrate. The joint comprises at least one ceramic key (104) partially accommodated in the first recess (102) and engaging the second member (32). The second member (32)comprises at least a metallic substrate.