Composite Shaft End Connections With Radial Preload for Axial Loads
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Solution Overview
Problem
Existing methods for joining fibre reinforced polymer (FRP) composite shafts with metal end fittings face challenges in transmitting axial loads efficiently and reliably, particularly in aerospace applications where robust and certifiable joints are required.
Innovation Solution
The use of helical and circumferential grooves with flank angles between 32° and 51° on FRP composite shafts, combined with a preload structure providing a radial biasing force, enhances the axial load transmission capacity and reduces sensitivity to friction variations, allowing for improved load distribution and fatigue performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard flank angle of 30° is used to match ISO metric screw threads, then ease of manufacture is improved, but axial load transmission capacity deteriorates
Solution Approach 1:
The patent changes the flank angle parameter from the standard 30° to an optimized range of 32°-51°. This parameter modification increases the radial biasing force between the composite shaft and metal end fitting, thereby improving axial load transmission capacity while maintaining manufacturability through standard machining processes.
2Strength
If the flank angle is increased to improve axial load capacity, then strength is improved, but weight increases
Solution Approach 1:
The patent optimizes the flank angle within a specific range (32°-51°) to achieve the best balance between axial load capacity and weight. This controlled parameter change ensures sufficient radial biasing force for high load transmission while avoiding excessive material addition that would increase weight.
3Strength
If a preload structure is added to provide radial biasing force, then axial load transmission is improved, but device complexity increases
Solution Approach 1:
The patent combines the preload structure with the metal end fitting into a single integrated component. This merging eliminates the need for separate preload devices, reducing assembly steps and overall device complexity while maintaining the necessary radial biasing force for improved axial load transmission.
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 configuration increases the axial load capacity, reduces weight, and improves joint reliability by optimizing the flank angle range, which balances increased radial biasing force with minimal weight addition, while maintaining resistance to friction changes due to environmental factors.
Implementation Method 1
a preload structure arranged to provide a radial biasing force to bias the first interference surface against the second interference surface
Implementation Method 2
the transmission of forces between the composite shaft and the end fitting is partly through the engagement of teeth (helical teeth or axial splines) provided on the metal end fitting with corresponding grooves in the composite shaft, and partly through friction between flat metal lands provided on the metal end fitting and the composite shaft
Data Source
AI summary
A fibre-reinforced polymer composite shaft for transmitting loads along a central axis is provided. The composite shaft comprises a first interface surface extending along the central axis and comprising at least one helical groove and/or a plurality of circumferential grooves for engaging with at least one corresponding helical ridge and/or a plurality of corresponding circumferential ridges of a second interface surface of an end fitting. The at least one helical groove and/or the plurality of circumferential grooves comprises at least one flank with a flank angle of between 32° and 51°. In such an assembly, a preload structure is arranged to provide a radial biasing force to bias the first interference surface against the second interference surface.