CMC Shroud Seal Segment with Elongated Pin Load Distribution
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Solution Overview
Problem
Ceramic matrix composite (CMC) materials used in gas turbine engines face limitations due to low allowable stress, high stiffness, and lower thermal expansion rates compared to metal alloys, leading to poor load distribution and limited use in high-pressure applications, especially in turbine shroud segments where machining is undesirable and results in short lifespans.
Innovation Solution
A segmented turbine shroud design featuring a carrier segment and CMC seal segments with elongated pins that provide increased structural support and reduced radial pressure loads, allowing for the use of CMC materials in high-pressure applications by distributing loads effectively and minimizing thermal stress through the use of elongated pins and varying cross-sectional dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CMC materials are used in turbine shroud segments, then resistance to high temperature degradation is improved, but allowable stress is reduced to an order of magnitude lower than metal alloys
Solution Approach 1:
The shroud is divided into multiple segments with each segment containing a CMC seal segment. This segmentation allows the CMC material to be used in high temperature zones while distributing mechanical loads across multiple components and mounting points, preventing any single point from exceeding the reduced allowable stress of the CMC material.
Solution Approach 2:
Metal alloy support structures and mounting pins serve as intermediary elements between the CMC seal segments. These metal components bear the higher mechanical loads and transfer them distributedly to the CMC segments, protecting the CMC material from exceeding its lower stress tolerance while maintaining structural integrity.
2Weight of moving object
If CMC seal segments are made with thin walls to reduce weight, then weight is reduced, but edge loading stresses increase due to small contact area between CMC wall and mounting pin
Solution Approach 1:
The mounting pins extend through the thickness of the CMC seal segment in the radial dimension, creating a distributed contact area along the pin length rather than concentrating stress at a single point or small surface area. This dimensional approach to load distribution reduces edge loading stresses while maintaining thin wall construction.
3Ease of manufacture
If CMC seal segments are machined with holes and slots for mounting pin attachment, then mounting capability is improved, but lifespan is reduced due to recession in hot humid environment
Solution Approach 1:
The mounting holes and slots are extracted from the CMC seal segment itself and relocated to metal alloy support structures. This separation removes the vulnerable machined features from the hot humid environment where they would recession, while the CMC segment retains its sealing function without compromised structural features.
Solution Approach 2:
The mounting functionality is copied from the CMC seal segment to separate metal alloy support structures. These metal structures serve as duplicates of the mounting function, allowing the CMC segment to avoid machining operations while achieving the same mounting capability through the support structures.
4Temperature
If CMC materials are used instead of metal alloys, then thermal expansion rate is reduced, but load distribution at transfer points deteriorates
Solution Approach 1:
The shroud is segmented into multiple sections with CMC seal segments separated by metal alloy support structures. This segmentation creates multiple load transfer points distributed around the turbine, preventing concentration of thermal expansion differential stresses at any single interface and improving overall load distribution.
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 design enhances the durability and lifespan of CMC materials in high-pressure environments by reducing edge loading and thermal stress, enabling the use of CMC materials in high-pressure gas turbine applications while maintaining efficiency and reducing assembly costs.
Implementation Method 1
The elongated pin has a lateral cross-sectional dimension of at least three-eighths of an inch... reducing edge loading and thermal stress
Implementation Method 2
a significantly lower thermal expansion rate than metallic components, leading to poor load distribution at transfer points
Implementation Method 3
a static blade track sealing shroud is designed to maximize the working air flowing through the turbine blades by minimizing the amount of air which leaks by the blade tips
Data Source
AI summary
A shroud for radially encasing a turbine in a gas turbine engine is provided. The shroud comprises a carrier which defines a pin-receiving carrier bore, and a ceramic matrix composite (CMC) seal segment comprising an arcuate flange with a surface facing the turbine and a part that defines a pin-receiving seal segment bore. The seal segment bore is radially spaced from the arcuate flange by a spacing flange which extends radially outward from the arcuate flange to effect receipt within the seal segment bore of an elongated pin. The elongated pin extends through the carrier bore and the seal segment bore, and the elongated pin has a lateral cross-sectional dimension of at least three-eighths of an inch.