Composite Tension Strut Helical Thread Interface
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Solution Overview
Problem
Existing methods for attaching end fittings to composite filament-wound transmission shafts, such as those used in tension/compression applications, face challenges in ensuring uniform load distribution across all filament layers, leading to weaker joints due to reliance on interlaminar shear strength, and require more material and complexity for structural efficiency.
Innovation Solution
A helical thread attachment mechanism is used on a composite filament-wound shaft, where filaments are angled and cut to expose ends in the interface region, allowing the thread to engage and compress all layers, providing a strong and efficient load transfer mechanism with a metallic end fitting that can be easily manufactured and assembled.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a simple mechanical press fit is used to attach the end fitting to the shaft, then the manufacturing process is simple, but the load transfer is poor because only the outermost plies are engaged
Solution Approach 1:
The filaments are pre-angled and cut to expose ends in the interface region before the end fitting is attached. This preliminary preparation ensures that when the end fitting is mounted, all filament layers are already positioned to engage with the helical thread, enabling superior load transfer without complex assembly procedures
Solution Approach 2:
The interface region is given special local treatment by angling and cutting filaments specifically in this zone. This creates a localized area where all plies have exposed ends that can engage with the end fitting, concentrating the load transfer capability exactly where it is needed while maintaining simple manufacturing elsewhere
2Strength
If more material is used to strengthen the joint, then the joint strength increases, but the weight increases reducing the strength-to-weight ratio
Solution Approach 1:
The joint utilizes the composite structure of the filament-wound shaft itself, engaging all filament layers through the helical thread mechanism. This approach leverages the high strength-to-weight ratio of composite materials to create a strong joint without adding excessive weight, maintaining the advantageous properties of the composite shaft
Solution Approach 2:
The helical thread provides a curved, progressive engagement path that distributes loads smoothly across all filament layers. This helical geometry allows efficient force transmission through the composite structure without requiring additional material, optimizing the strength-to-weight ratio by utilizing the natural curvature and layering of the filament-wound shaft
3Strength
If a helical thread is used to engage all filament layers, then the load distribution across plies is improved, but the manufacturing complexity increases
Solution Approach 1:
The filaments are pre-angled and cut to expose ends in the interface region before assembly. This preliminary preparation ensures that when the end fitting is mounted, all filament layers are already positioned to engage with the helical thread, enabling superior load transfer without complex assembly procedures
Solution Approach 2:
The helical thread automatically engages with exposed ends of filaments from all layers as it is screwed into the shaft. The structure is self-assembling in the sense that the thread profile is designed to naturally capture and distribute loads across all plies through its helical geometry, reducing the need for complex alignment procedures or additional 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 enhances the strength-to-weight ratio of the joint, ensuring robust force transmission and reducing material usage while maintaining structural efficiency, making it suitable for tension and compression forces with improved load sharing across multiple fibre plies.
Implementation Method 1
During the mounting process, the helical thread is driven into the composite shaft, between the fibre ends, compressing the fibres and thus forming a very strong attachment
Implementation Method 2
The thread cuts into and removes material from the composite shaft
Data Source
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AI summary
A composite filament-wound shaft with an end fitting mounted on an interface region on at least one end of said shaft, wherein in said interface region filaments of the filament-wound shaft are angled with respect to the shaft axis such that they follow a path with a radial component and have been cut so as to expose the ends of said filaments in said interface region; and wherein said end fitting comprises a helical thread engaging with said interface region. The helical threaded engagement provides excellent load transmission of axial forces and is therefore well suited to tension and compression elements. The joint provides a low cost and low weight interface.