Composite Shaft End Fitting With Interference Preload Joint
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Solution Overview
Problem
Joining composite structural components made of polymer matrix composite materials to metallic components for axial load transmission is challenging, particularly in the aerospace industry, due to issues with weight, complexity, and joint robustness, as existing methods require additional layers and materials that increase size and weight, and may lead to fretting and wear.
Innovation Solution
A composite shaft with an end fitting and a preload structure in an interference fit, applied after the end fitting is mounted, to bias the shaft and increase joint strength and fatigue resistance, reducing assembly stress and eliminating the need for additional frictional surfaces, thus minimizing weight and heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flat lands are provided in the tooth profile to increase frictional engagement, then wear resistance is improved, but end fitting length and weight increase significantly
Solution Approach 1:
The invention extracts and removes the flat lands from the tooth profile, retaining only the cutting teeth. This eliminates the harmful portion (flat lands that cause weight increase) while preserving the essential function (force transmission through teeth). The shaft is designed with sufficient length to provide adequate engagement without requiring extended flat land portions.
Solution Approach 2:
Instead of using flat lands to generate friction, the invention inverts the approach by using the absence of flat lands and relying on the precision fit and cutting teeth alone. The tooth profile is inverted from a conventional design with friction-generating surfaces to a design where friction is minimized and force transmission is achieved through direct tooth-to-shaft engagement.
2Strength
If pressing or screwing the end fitting onto the shaft is performed to achieve secure connection, then joint strength is improved, but assembly friction generates heat and requires additional composite layers
Solution Approach 1:
The invention applies preliminary action by pre-forming the shaft with a slightly reduced diameter in the engagement region before end fitting assembly. This pre-prepared geometry allows the end fitting to be installed with minimal assembly force, preventing excessive heat generation while ensuring secure connection. The shaft is prepared in advance to facilitate low-friction assembly.
Solution Approach 2:
The invention changes the geometric parameter of the shaft by reducing its diameter in the engagement region relative to the main shaft body. This parameter modification creates an interference fit that provides strong joint strength without requiring high assembly forces, thereby minimizing heat generation during installation.
3Ease of manufacture
If additional layers of composite are added to combat assembly friction, then assembly feasibility is improved, but component size and weight increase
Solution Approach 1:
The preliminary reduction in shaft diameter is performed during the composite manufacturing process itself, integrating the solution into the base fabrication rather than adding separate reinforcement layers. This eliminates the need for additional weight-bearing layers while ensuring assembly feasibility is built into the design.
Solution Approach 2:
By changing the diameter parameter locally in the engagement region, the invention achieves proper interference fit for assembly without requiring additional composite layers. The parameter change is sufficient to provide both assembly feasibility and joint strength without weight penalties.
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
The preload structure enhances joint strength and fatigue resistance while reducing weight and assembly loads, resulting in a more efficient and robust connection with improved force transmission and reduced material usage.
Implementation Method 1
a preload structure arranged to provide a biasing force to bias the composite shaft against the end fitting; wherein the preload structure is in an interference fit with the composite shaft
Data Source
AI summary
A composite shaft with an end fitting mounted on an interface region on at least one end of said shaft, and a preload structure arranged to provide a biasing force to bias the composite shaft against the end fitting; wherein the preload structure is in an interference fit with the composite shaft. The preload structure is applied to the composite shaft in a subsequent operation to the mounting of the end fitting to the shaft.