Composite Shaft End Fitting With Post-Assembly Interference Preload
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Joining composite structural components to metallic components for axial load transmission in aerospace applications is challenging due to weight and complexity issues, with existing methods requiring additional layers and materials that increase size and stress during assembly.
Innovation Solution
A composite shaft with an end fitting and a preload structure in an interference fit, applied after mounting, to bias the shaft and increase joint strength and fatigue resistance, reducing assembly stress and weight by eliminating flat lands and optimizing tooth angle for efficient force transmission.
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 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 essential cutting teeth for force transmission. This removal of unnecessary components directly reduces the end fitting length and weight while maintaining the core functionality of the joint.
2Reliability
If flat lands are provided in the tooth profile to provide frictional engagement and preload, then joint stability is improved, but additional assembly loads and heat generation occur during mounting
Solution Approach 1:
The flat lands that cause frictional heating and assembly stress are completely removed from the tooth profile. The invention achieves joint stability through the cutting teeth engagement alone, eliminating the source of harmful thermal and mechanical effects during assembly.
Solution Approach 2:
The invention converts the potential harm of friction during assembly into a benefit by using the cutting teeth to create a precise interference fit. The controlled material removal during assembly creates optimal contact conditions without the harmful side effects of flat land friction.
3Reliability
If additional layers of composite are added to combat assembly loads from pressing or screwing end fittings, then assembly durability is improved, but the size and weight of the component increase
Solution Approach 1:
The invention extracts and eliminates the need for additional protective composite layers by removing the source of excessive assembly loads (the flat lands). The streamlined tooth profile without flat lands reduces assembly stress to levels that the standard composite shaft can handle without reinforcement.
4Reliability
If the end fitting is made longer to include flat lands, then frictional engagement and preload are improved, but the overall joint complexity increases
Solution Approach 1:
The invention removes the flat lands from the tooth profile, simplifying the joint design to its essential elements. The frictional engagement function is achieved through the optimized cutting teeth geometry alone, eliminating the need for complex multi-feature profiles.
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 solution results in a structurally efficient joint with improved strength-to-weight ratio, reduced assembly loads, and enhanced fatigue resistance, allowing for lighter, more efficient composite structures with minimal stress during assembly.
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
Implementation Method 2
the transmission of forces between the composite shaft and the end fitting is partly through the teeth (helical teeth or axial splines) that are provided on the metal end fitting and cut into the composite shaft, and partly through friction between the composite shaft and the flat metal lands
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.