Low-Ductility CMC Shroud Mounting with Elastic Springs
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Solution Overview
Problem
The challenge in gas turbine engines is to support ceramic matrix composite (CMC) shrouds without inducing failure due to thermal expansion mismatch with metallic structures, as traditional mechanical fasteners and rigid connections cause high stresses and affect turbine clearance control.
Innovation Solution
A turbine shroud mounting assembly that includes an annular support member, a spring-mounted CMC shroud, and a spring element to resiliently urge the shroud into a concentric position, allowing for thermal growth while preventing axial movement and rotation, thereby reducing stress and maintaining turbine clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional mechanical fasteners or rigid mechanical connections are used to hold the CMC shroud to the engine, then the shroud can be securely mounted, but very high stresses are induced into the shroud due to thermal expansion mismatch, causing potential failure
Solution Approach 1:
The patent changes the mechanical properties of the mounting system by introducing elastic springs that allow dynamic adjustment of mounting forces. The springs transform the rigid mechanical connection into a compliant system that can accommodate thermal expansion differences between CMC and metal structures, reducing induced stresses while maintaining secure mounting.
Solution Approach 2:
The elastic spring elements act as intermediaries between the CMC shroud and the metallic engine structure. These springs absorb the thermal expansion mismatch by deforming elastically, preventing direct stress transmission from the metal structure to the brittle CMC shroud while still providing secure mechanical retention.
2Stability of the object's composition
If rigid mechanical connections are used to secure the shroud, then mounting stability is achieved, but turbine clearance control is adversely affected due to restricted thermal growth
Solution Approach 1:
The patent transitions from a static rigid mounting system to a dynamic elastic mounting system. The spring elements allow the shroud to dynamically adjust its position in response to thermal growth, maintaining stable mounting while enabling the necessary radial movement for proper turbine clearance control during operation.
3Temperature
If CMC materials are used for the shroud, then high-temperature capabilities and weight are improved, but the low tensile ductility makes the material susceptible to failure under thermal stress
Solution Approach 1:
The patent changes the stress state parameters by introducing compliant spring mountings that reduce the magnitude of thermal stresses transmitted to the CMC shroud. This allows the CMC material to operate at high temperatures without exceeding its low ductility failure threshold, as the elastic mounting absorbs thermal expansion mismatches.
4Reliability
If metallic shroud structures are used, then ductility and stress resistance are maintained, but weight and cooling flow requirements increase significantly
Solution Approach 1:
The patent employs a composite mounting system combining elastic spring elements with the CMC shroud structure. This hybrid approach allows the use of lightweight CMC materials for the shroud itself while using metallic spring elements to provide the necessary mechanical compliance and stress absorption, achieving both weight reduction and stress resistance.
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
This solution enables the use of CMC shrouds with reduced weight, cooling flow requirements, and part count, improving maintainability and performance by allowing unrestricted radial growth without shroud breakage, achieving a 66% weight reduction and 50% cooling flow reduction compared to prior designs.
Implementation Method 1
a spring mounted between the support member and the shroud and arranged to resiliently urge the shroud to a concentric position within the structural member
Implementation Method 2
a spring element disposed between the turbine shroud and an axially adjacent static element arranged to resiliently urge the shroud axially against a portion of the support member
Implementation Method 3
CMCs have a coefficient of thermal expansion (CTE) in the range of about (2.7-9)X10^-6
Data Source
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AI summary
A turbine shroud apparatus is provided for a gas turbine engine having a central axis. The apparatus includes: (a) an annular support member (14); (b) a turbine shroud (12) disposed in the support member (14), the shroud (12) being a continuous ring comprising a low-ductility material and having opposed flowpath and back surfaces, and opposed forward and aft ends; and (c) a spring (32) mounted between the support member (14) and the shroud (12) and arranged to resiliently urge the shroud (12) to a concentric position within the support member (14).