Flexible Abutment Links for CMC Afterbody Assemblies
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Solution Overview
Problem
The existing flexible fixing lugs used to mount ceramic matrix composite (CMC) parts in aeronautical engines struggle to resist ultimate loads without increasing the assembly's mass or stiffness, contradicting the objective of mass savings and potentially leading to detachment under extreme conditions.
Innovation Solution
Incorporating axial and radial stop elements into the flexible fixing lugs allows for resistance to ultimate loads without reinforcement, ensuring the CMC parts remain securely attached to metallic components by forming additional force transmission paths, thereby reducing stress on the CMC parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of flexible fixing lugs is increased to resist ultimate loads, then the strength and reliability improve, but the mass of the assembly increases significantly
Solution Approach 1:
The fixing lug is segmented into multiple functional zones: a first thickness region for flexibility under normal/limit loads, and a second thickness region (reinforcement zone) for resisting ultimate loads. This segmentation allows each region to be optimized for its specific function, preventing mass increase in the flexible connection zone while ensuring ultimate load resistance through localized reinforcement.
Solution Approach 2:
The reinforcement zone is positioned locally at the attachment part of the fixing lug where ultimate load resistance is critical. This local quality change (increased thickness) is applied only where needed rather than uniformly throughout the entire lug, thereby ensuring reliability under extreme conditions while minimizing the overall mass increase of the assembly.
2Strength
If the thickness of flexible fixing lugs is increased to resist ultimate loads, then the strength improves, but the flexibility of the connection deteriorates
Solution Approach 1:
The fixing lug is divided into a flexible connection zone (first thickness) and a reinforcement zone (second thickness). The flexible connection zone maintains its original thickness to preserve elasticity and flexibility under normal operating conditions, while the reinforcement zone provides additional strength where ultimate load resistance is required, thus resolving the contradiction between flexibility and strength.
Solution Approach 2:
The reinforcement is applied locally at the attachment part of the fixing lug rather than uniformly throughout. This localized quality enhancement ensures that the connection remains flexible in the regions where thermal expansion compensation is needed, while providing the necessary strength in the specific region where ultimate load resistance is critical.
3Strength
If the thickness of fixing lugs is increased to resist ultimate loads, then the strength improves, but the mass savings objective of using CMC parts is compromised
Solution Approach 1:
The fixing lug structure is segmented into a standard thickness region (for flexibility and mass efficiency) and a reinforcement zone with increased thickness (for ultimate load resistance). This segmentation ensures that mass is added only where structurally necessary, preserving the overall mass savings objective of using CMC parts while ensuring adequate strength under extreme conditions.
Solution Approach 2:
The reinforcement zone is positioned locally at the attachment part of the fixing lug where ultimate load resistance is most critical. This localized approach ensures that the additional mass is minimized and concentrated only where needed for safety, thereby maintaining the mass savings benefits of CMC usage in the majority of the assembly.
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 design effectively maintains the flexibility of the connection while ensuring the CMC parts can withstand ultimate loads, preventing detachment and reducing stress concentrations, thus achieving the goal of mass savings while ensuring structural integrity.
Implementation Method 1
the CMC part is mounted on the casing made of metallic material by means of elastically flexible fixing lugs... In order to compensate for the differential expansions between these elements
Implementation Method 2
These parts have a low coefficient of thermal expansion compared to the metal engine cases on which they must be mounted. In order to compensate for the differential expansions between these elements
Data Source
Figure 1
Figure 2~5
Figure 6~9
AI summary
The invention relates to an afterbody assembly for an aeronautical engine including an annular part (60), made of metal material and rigidly connected to the aeronautical engine, and to an afterbody part (20), made of ceramic matrix composite material, the afterbody part (20) being mounted onto the annular part (60) by resiliently flexible mounting lugs (70) and having a first end (71) attached onto the annular part (60) and a second end (72) attached onto the upstream portion of the afterbody part (20). Each mounting lug (70) includes an axial abutment element (720) radially extending from the second end (72) of the lug and at least partially facing the first end (71). The mounting lug (70) also includes a radial abutment element (721) on the second end (72) of the lug, the radial abutment element (721) being at least partially above the first end (71).