Composite Shaft End Fitting With Even Joint Pressure Distribution
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Solution Overview
Problem
Existing composite structural components face challenges in forming robust and certifiable end connections with metallic components, particularly in the aerospace industry, where complex geometry and uneven contact pressure distribution lead to weight and strength issues in axial load transmission.
Innovation Solution
A composite shaft with a tapered interface surface and a preload structure that varies contact pressure along its length, ensuring even load distribution across the joint by shaping the shaft and preload structure to compensate for axial pressure variations, thereby enhancing joint strength and reducing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flat lands are provided in the tooth profile to improve wear properties through frictional engagement, then the wear resistance is improved, but the length of the end fitting increases significantly resulting in increased weight
Solution Approach 1:
The invention extracts and eliminates the flat lands from the tooth profile, retaining only the cutting teeth for force transmission. This removes the source of excessive friction during assembly while preserving the essential load-bearing function through the teeth engagement alone.
Solution Approach 2:
The invention changes the tooth profile parameters by removing the flat land portions, thereby altering the friction characteristics during assembly. This allows for reduced assembly friction and lower required assembly loads without compromising the wear resistance during operation, as the teeth still provide adequate engagement.
2Reliability
If high assembly torque is applied to provide preload on the joint and prevent fretting, then the joint reliability is improved, but the friction heats up the composite shaft requiring additional composite layers that increase size and weight
Solution Approach 1:
The invention extracts and removes the flat lands that cause excessive friction during assembly. By eliminating this friction source, the assembly process generates less heat, removing the need for additional protective composite layers and reducing the overall weight of the composite shaft.
Solution Approach 2:
The invention converts the potentially harmful effect of friction (heat generation) into a beneficial outcome by eliminating the flat lands. This reduces assembly friction to acceptable levels, preventing heat buildup that would otherwise require additional composite layers for protection.
3Ease of manufacture
If metals are used for end connections to achieve complex geometry efficiently, then the manufacturing efficiency is improved, but the weight of the component increases
Solution Approach 1:
The invention uses composite materials (carbon fibre reinforced polymer) for both the shaft and the end fitting, eliminating the need for metallic end connections. This maintains the weight advantages of composite structures while achieving the required complex geometry through composite manufacturing techniques such as filament winding.
Solution Approach 2:
The invention makes the composite material universal by using it for both the shaft and the end fitting components. This eliminates the need for metal-composite joints and allows the composite material to perform multiple functions structurally, maintaining consistency in material properties and weight characteristics throughout the assembly.
4Reliability
If additional layers of composite are added to combat assembly loads, then the assembly process reliability is improved, but the size and weight of the component increase
Solution Approach 1:
The invention extracts and eliminates the flat lands from the tooth profile, which are the source of excessive assembly friction. By removing this friction source, the assembly process becomes less demanding, eliminating the need for additional composite layers that would otherwise be required to withstand high assembly loads.
Solution Approach 2:
The invention applies only the necessary amount of friction in the tooth profile by eliminating the flat lands. This partial action approach provides sufficient engagement for load transmission without the excessive friction that would require additional protective composite layers, achieving the minimum required reliability without over-engineering.
Data Source
Figure 1a
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AI summary
A composite shaft (1) with an end fitting (2) mounted on at least one end of said shaft and a preload structure (7) arranged to provide a biasing force to bias the composite shaft against the end fitting; wherein the end fitting has a first interface surface, the first interface surface being tapered at an angle to the shaft axis; wherein the shaft has a second interface surface for engagement with the first interface surface, the second interface surface being tapered at an angle to the shaft axis, the second interface surface extending axially from a first end to a second end, the shaft being thicker at the second end than at the first end; wherein the shaft has a third interface surface; wherein the preload structure has a fourth interface surface for engagement with the third interface surface; and wherein at least one of the shaft and the preload structure is shaped such that the contact pressure of the third interface against the fourth interface increases from the first end of the shaft to the second end of the shaft. The varying contact pressure of the third interface against the fourth interface (i.e. the contact pressure of the preload structure against the composite shaft) compensates for the varying contact pressure between the first interface and the second interface such that the overall contact pressure between the composite shaft and the end fitting is more even across the axial length of the joint. Thus the force transfer between the composite shaft and the end fitting is more evenly distributed across the joint and therefore more evenly distributed across the composite layers so that overall joint strength is increased (or conversely allowing a reduced size of part for the same equivalent strength, thereby saving weight).