CMC Combustor Liner Attachment With Spring Retention 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 CMC materials, which cannot withstand the torqueing of traditional bolt/screw type fasteners, leading to issues like cracking and delamination under thermal expansion and contraction.
Innovation Solution
A combustor liner attachment assembly that includes a non-metallic liner with a spring element and protrusion feature, where the protrusion is radially outward from the liner and disposed within a recessed segment of the spring element, axially retaining the liner, and a metal fastener secures the liner and spring element together with a nut, avoiding direct threading through the CMC material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional bolt/screw type fasteners are used to attach the CMC liner to the metallic bulkhead, then the attachment strength is improved, but the CMC liner cracks and delaminates due to torqueing and thermal expansion/contraction
Solution Approach 1:
The attachment system is segmented into multiple components: a fastener body, a separate retainer ring, and a fastener. The retainer ring is installed on the bulkhead first, creating a modular assembly that separates the fastening function from the liner attachment function, thereby protecting the CMC liner from direct torqueing
Solution Approach 2:
The retainer ring acts as an intermediary component between the metallic bulkhead and the CMC liner. It receives the fastener and provides a bearing surface for the liner, mediating the mechanical connection while preventing direct stress transfer to the brittle CMC material
2Device complexity
If the CMC liner is directly attached to the metallic bulkhead, then the attachment is simple, but thermal expansion and contraction cause cracking and delamination
Solution Approach 1:
The retainer ring serves as a mediator between the metallic bulkhead and the CMC liner, absorbing thermal expansion and contraction stresses. This intermediary component protects the liner from direct thermal stress while maintaining a secure attachment
Solution Approach 2:
The attachment system accommodates parameter changes in temperature by allowing controlled movement and expansion through the retainer ring mechanism. The retainer ring's geometry and material properties enable it to absorb thermal stresses without transferring them to the CMC liner
3Reliability
If a mechanical fastener system is used that avoids threading through the CMC material, then the liner durability is improved, but the attachment mechanism becomes more complex
Solution Approach 1:
The attachment mechanism is segmented into distinct functional components: the retainer ring provides structural support and stress distribution, while the fastener provides secure attachment. This segmentation allows each component to be optimized for its specific function, improving durability while maintaining reasonable complexity
Solution Approach 2:
The threading function is extracted from the CMC liner material and relocated to the metallic bulkhead and fastener components. The retainer ring is installed on the bulkhead first, and the fastener threads into the retainer ring rather than the liner, completely avoiding stress concentrations in the CMC material
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 liner without introducing stress concentrations, allowing for thermal growth and reducing the frequency of repairs by using a mechanical fastener that is not threaded through the CMC material, thereby enhancing the durability and reliability of the attachment.
Implementation Method 1
a spring element located adjacent to a portion of the liner and operatively coupled to a stationary structure
Data Source
AI summary
A combustor liner panel attachment assembly includes a liner extending from a first end to a second end, and circumferentially to partially define a combustion zone. The assembly also includes a spring element located adjacent to a portion of the liner and operatively coupled to a stationary structure, the spring element having a recessed segment. The assembly further includes a protrusion feature extending radially outwardly from the liner, the protrusion feature disposed within the recessed segment of the spring element to axially retain the liner.