BOAS Segment Composite Alloy Thermal Fatigue
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Solution Overview
Problem
Gas turbine engine blade outer air seal (BOAS) segments are prone to cracking due to thermal mechanical fatigue resulting from differential thermal expansion in the harsh environment of the high-pressure turbine section, leading to premature engine removal and replacement.
Innovation Solution
A BOAS segment is designed with a body formed of a first metal alloy and a recess on the inwardly facing side filled with a second metal alloy having a lower coefficient of thermal expansion, which reduces thermal mechanical fatigue cracking by mitigating residual stresses from differential thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single material is used for the BOAS segment body, then the manufacturing process is simple and cost-effective, but the segment is prone to thermal mechanical fatigue cracking due to differential thermal expansion
Solution Approach 1:
The BOAS segment body is constructed from two different materials: a first material forming the main body and a second material with a lower coefficient of thermal expansion forming a layer on the inwardly facing side. This composite structure allows the second material to compensate for differential thermal expansion between the inwardly facing side (exposed to hot gases) and the outwardly facing side (cooled), thereby reducing residual tensile stresses and preventing thermal mechanical fatigue cracking while maintaining manufacturing feasibility through established composite material techniques.
2Reliability
If the inwardly facing side of the BOAS segment is exposed to hot gases, then the segment can maintain its sealing function, but differential thermal expansion causes compressive stress that exceeds the yield point and leads to cracking
Solution Approach 1:
The inwardly facing side of the BOAS segment is provided with a layer of second material that has different thermal expansion characteristics than the main body material. This local modification allows the surface layer to better accommodate thermal expansion during operation while the bulk material maintains structural strength. The layered structure creates a gradient that manages stress distribution, preventing the compressive stress from exceeding the yield point and avoiding cracking that would compromise the sealing function.
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 solution effectively reduces the likelihood of cracking in BOAS segments by managing thermal expansion differentials, thereby extending the service life of the engine and reducing maintenance needs.
Implementation Method 1
the radially inboard facing side of the body of each BOAS segment is exposed directly to the hot gases passing through the turbine section, the BOAS segments are subject to differential thermal expansion. That is, the radially inboard facing side of the body of each BOAS segment, due to exposure to a higher temperature than the radially outboard side, undergoes thermal expansion at a higher rate than the outboard side of the body of the BOAS segment
Data Source
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AI summary
A blade outer air seal (BOAS) segment for a gas turbine engine is disclosed wherein the formation of cracks due to thermal mechanical fatigue in the body of the disclosed BOAS segment is minimized, if not eliminated, through a unique construction of the disclosed BOAS segment, whether original equipment manufacture or a repaired BOAS. The segment (44) has a body (50) formed in part of a first metal alloy and in part of a second metal alloy, the second metal alloy having a thermal coefficient of expansion that is less than the thermal coefficient of expansion of the first metal alloy. A method for manufacture of a BOAS segment and a method for modifying a BOAS segment are also disclosed.