Spring-Retained CMC Combustor Liner Attachment for Thermal Growth
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Solution Overview
Problem
Robust and efficient attachment of ceramic matrix composite (CMC) liners to metallic bulkheads in gas turbine engines is challenging due to the brittleness of ceramic materials and the stress introduced by traditional bolt/screw fasteners, leading to issues like cracking and delamination under thermal expansion and contraction.
Innovation Solution
A combustor liner attachment assembly that uses a metal spring element, such as a ship-lap panel, operatively coupled to the bulkhead structure, with a non-metallic ceramic matrix composite liner and a metal spacer to distribute mechanical fastener loads, avoiding direct threading through the CMC material and utilizing protrusion features and recesses for axial securement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional bolt/screw fasteners are used to attach the CMC liner to the metallic bulkhead, then the attachment strength is improved, but the CMC liner is subjected to stress concentrations that cause cracking and delamination
Solution Approach 1:
A compliant intermediary layer is introduced between the CMC liner and metallic bulkhead to distribute fastener loads and accommodate thermal expansion differences. This compliant layer acts as a stress-distributing medium that prevents stress concentrations from reaching the brittle CMC material, thereby maintaining both attachment strength and liner integrity.
Solution Approach 2:
The fastener attachment mechanism is modified to change the stress distribution parameters. Instead of concentrated point loads from traditional fasteners, the system uses a compliant layer that transforms the load distribution into a more uniform stress field, reducing peak stresses below the cracking threshold of CMC material.
2Reliability
If the CMC liner is rigidly attached to the bulkhead, then the attachment reliability is improved, but the thermal expansion and contraction causes stress concentrations leading to cracking
Solution Approach 1:
The attachment system transitions from a rigid, static connection to a dynamic, compliant connection that can adapt to thermal cycles. The compliant intermediary layer allows the liner to expand and contract thermally while maintaining attachment, transforming the system from statically constrained to dynamically adaptive.
Solution Approach 2:
The design explicitly accounts for thermal expansion by incorporating a compliant layer with appropriate thermal and mechanical properties. This layer accommodates the differential thermal expansion between the CMC liner and metallic bulkhead, preventing stress buildup that would lead to cracking while maintaining reliable attachment.
3Reliability
If a compliant intermediary layer is used to distribute fastener loads, then the stress concentrations are reduced, but the device complexity increases
Solution Approach 1:
The compliant intermediary layer is integrated with the existing fastener system and bulkhead structure, merging multiple functions into a unified attachment assembly. The compliant layer serves simultaneously as a stress-distributing element, thermal expansion accommodator, and sealing interface, reducing the need for separate components.
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 effectively secures the CMC liner without inducing stress concentrations, reducing the risk of cracking and delamination, and allows for thermal growth, thereby enhancing the durability and reliability of the combustor assembly.
Implementation Method 1
a combustor liner attachment assembly that uses a metal spring element, such as a ship-lap panel, operatively coupled to the bulkhead structure
Implementation Method 2
the brittleness of ceramic materials and the stress introduced by traditional bolt/screw fasteners, leading to issues like cracking and delamination under thermal expansion and contraction
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A combustor liner panel attachment assembly includes a liner (130) extending from a first end to a second end, and circumferentially to partially define a combustion zone (110). The assembly also includes a spring element (140) located adjacent to a portion of the liner and operatively coupled to a stationary structure, the spring element having a recessed segment (146). The assembly further includes a protrusion feature (142) extending radially outwardly from the liner, the protrusion feature disposed within the recessed segment of the spring element to axially retain the liner.