Composite Resilient Tabs for Aeroengine Exhaust Casing

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Solution Overview

Problem

The use of metal fastener tabs for composite material parts in aeroengine after-bodies is weight-intensive, complex to manage sealing, and costly, as they are needed to accommodate differential thermal expansion between composite and metal parts.

Innovation Solution

Incorporating axisymmetric composite material parts with annular portions featuring slots that define resilient fastener tabs, which attach directly to the metal exhaust casing, eliminating the need for metal fastener tabs and allowing for direct attachment to compensate for thermal expansion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If metal fastener tabs are used to fasten composite material parts to the exhaust casing, then the differential thermal expansion between composite and metal parts can be compensated, but the weight of the assembly increases significantly

Engineering Contradiction:

Improvecompensation of differential thermal expansionVSAvoidweight of fastener tabs

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent merges the fastener tab function directly into the composite material part by integrating resilient tabs made of the same composite material into the part structure itself. This eliminates the need for separate metal fastener tabs while maintaining the ability to compensate for differential thermal expansion between the composite part and metal exhaust casing.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent changes the material parameter of the fastener tabs from metal to composite material, matching the thermal expansion properties of the main part. This parameter change allows the tabs to expand and contract with the composite part rather than creating additional differential expansion issues, while significantly reducing weight.

Inventive Principle:

Principle #35Parameter changes

2Strength

If metal fastener tabs are used to fasten composite material parts, then mechanical strength to withstand loads can be provided, but the cost of fabrication increases

Engineering Contradiction:

Improvemechanical strength of fastener tabsVSAvoidfabrication cost of fastener tabs

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The fastener tabs are merged with the composite material part as an integrated structure. The tabs are formed as part of the same manufacturing process (autoclave curing) as the main part, eliminating separate fabrication and assembly steps. This integration reduces fabrication cost while maintaining mechanical strength through the composite material's inherent properties and optimized tab geometry.

Inventive Principle:

Principle #5Merging (Combining)

3Strength

If metal fastener tabs are used for fastening, then the connection between composite part and exhaust casing can be secured, but the complexity of managing sealing increases

Engineering Contradiction:

Improveconnection strengthVSAvoidsealing management complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent uses homogeneous composite material for both the main part and the integrated fastener tabs, creating a uniform material system. This homogeneity simplifies sealing management because the entire assembly (part plus tabs) can be treated as a single unit for sealing purposes, rather than managing interfaces between dissimilar metal and composite materials.

Inventive Principle:

Principle #33Homogeneity

4Strength

If separate metal fastener tabs are used, then the fastening function can be provided, but the assembly process becomes more complex

Engineering Contradiction:

Improvefastening functionVSAvoidassembly complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The fastener tabs are merged with the composite material part as an integrated structure formed in the same autoclave curing process. This integration eliminates the need for separate fastener tab components and their associated attachment operations, significantly simplifying the assembly process while maintaining the fastening function through the compliant tab design that accommodates thermal expansion.

Inventive Principle:

Principle #5Merging (Combining)

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 reduces weight, simplifies assembly, and lowers costs by eliminating the need for metal fastener tabs while effectively managing thermal expansion between composite and metal parts.

Implementation Method 1

resilient fastener tabs, each slot co-operating with an arm of the exhaust casing... serve to compensate differential thermal expansion relative to the exhaust casing

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS10066581B2Structure for fastening after-body parts of an aeroengine

Publication Date: 2018.09.04 SAFRAN NACELLES

AI summary

The invention relates to an aeroengine after-body assembly comprising an exhaust casing made of metal having a plurality of arms extending radially between an inner shroud and an outer shroud. The assembly comprises at least one axisymmetric part made of composite material extending between an upstream end fastened to said exhaust casing and a downstream end that is free. In accordance with the invention, the axisymmetric part has an annular portion at its upstream end, which annular portion includes a plurality of slots defining between them a plurality of resilient fastener tabs. Each slot co-operates with an arm of the exhaust casing, which further includes fastener parts attached to the resilient fastening tabs.