Tapered Composite Shaft Joint for Multi-Layer Load Transfer
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Solution Overview
Problem
Existing methods for attaching end fittings to composite transmission shafts, such as those made of Polymer Matrix Composites, face challenges in ensuring uniform load distribution across multiple layers, leading to weaker joints due to reliance on interlaminar shear strength and potential delamination under high forces.
Innovation Solution
A tapered interface between the shaft and end fitting, with a toothed surface that engages multiple layers of the shaft, allowing for simultaneous contact and distributing forces effectively, reducing heat buildup and assembly time, and utilizing a lubricant for easier engagement.
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 assembly process is simple, but the load transfer is poor because the end fitting only interfaces with the outermost plies and relies on weak interlaminar shear strength
Solution Approach 1:
The end fitting is segmented into multiple teeth that engage with different plies of the composite shaft at different depths. This segmentation allows the load to be distributed across multiple layers simultaneously, with each tooth engaging a specific ply, thereby overcoming the limitation of simple press-fit connections that only engage the outermost layer.
Solution Approach 2:
The solution transitions from a two-dimensional surface contact (press fit on outer surface) to a three-dimensional engagement where teeth penetrate through multiple plies at different depths. This dimensional change enables simultaneous engagement with multiple layers, distributing the load throughout the composite structure rather than relying on weak interlaminar shear at the surface.
2Ease of operation
If shallow splines or threaded connections are used, then the assembly is easier, but the load distribution among filament layers remains poor
Solution Approach 1:
The end fitting incorporates multiple segmented teeth of varying depths that engage with different plies of the composite shaft. This segmentation ensures that each tooth can engage its corresponding ply effectively, distributing the load across all filament layers rather than concentrating it at the surface or relying on weak threaded connections.
Solution Approach 2:
Different teeth are designed with different engagement depths and geometries to match the specific ply structure of the composite shaft. This local customization of tooth characteristics ensures optimal engagement with each ply, maximizing load distribution while maintaining assembly ease.
3Reliability
If multiple layers are engaged simultaneously, then load distribution is improved, but the assembly process becomes more complex
Solution Approach 1:
The end fitting is designed with segmented teeth that naturally engage multiple plies during a single assembly operation. This segmentation achieves multi-layer load distribution without requiring complex multi-step assembly processes, as the teeth's varying depths automatically engage different layers simultaneously during installation.
Solution Approach 2:
The tapered geometry and tooth configuration enable the end fitting to self-align and engage multiple plies automatically during assembly. The design performs the complex task of multi-layer engagement through its inherent geometry, eliminating the need for additional alignment steps or complex assembly procedures.
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 tapered interface ensures robust and efficient force transmission with a high strength-to-weight ratio, reducing material usage and manufacturing complexity, while maintaining structural integrity across multiple layers, thus enhancing the joint's durability and efficiency.
Implementation Method 1
utilizing a lubricant for easier engagement
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
A composite shaft (1) with an end fitting (2) mounted on an interface region (6) on at least one end of said shaft, wherein in said interface region the shaft is tapered; and wherein said end fitting comprises a surface with matching taper (7), the surface engaging with said interface region. Tapering the shaft and the end fitting means that the process for engaging the two together can be accomplished in less time and over a short distance. The end fitting surface may be a toothed surface of either axial spline teeth or helical thread teeth. The taper allows a certain amount of axial overlap between the two parts before contact is made between the teeth of the end fitting and the interface region of the shaft. When contact is made, it is made along substantially the whole of the interface region simultaneously. Further axial movement between the two parts results in further overlap of the two parts and also engagement of the toothed surface with the shaft so as to permit force transmission between the two parts. The taper on the shaft exposes a significant cross section of the shaft to the end fitting and results in engagement with the end fitting across that exposed portion. This ensures that engagement is not simply with the outer surface portion of the shaft, reducing the chance of delamination when force is transmitted across the joint.