Composite Shaft Joint with Spline Interface
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Solution Overview
Problem
Existing composite shafts face challenges in evenly distributing torque loads between the composite material and metallic end fittings, particularly in aerospace applications where adhesive bonds are unreliable for integrity assessment.
Innovation Solution
A concentric cylindrical torsional joint with serrated splined internal features is used for a mechanical interface, combined with an optional secondary adhesive bond for load distribution and environmental protection, utilizing a wedge-shaped inner layer to control local geometry and facilitate an external interference fit with metallic fittings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive bonds are used to attach metallic end fittings to composite shafts, then load distribution may be improved, but reliability deteriorates due to inability to assess bond integrity in aerospace applications
Solution Approach 1:
The patent divides the attachment system into two independent parts: a primary mechanical joint (spline interface) and an optional secondary adhesive bond. This segmentation allows the mechanical joint to provide reliable load transfer that can be assessed through NDT methods, while the adhesive provides supplementary load distribution without being the sole load path, thus resolving the contradiction between load distribution and reliability assessment.
Solution Approach 2:
The mechanical spline joint acts as an intermediary that provides a verifiable load path between the composite shaft and metallic end fittings. This intermediary mechanism enables reliable assessment of joint integrity through NDT methods while still allowing for improved load distribution when adhesive is added as a secondary path.
2Strength
If composite shafts use high modulus carbon fibre reinforced plastics to increase whirling resistance, then torsional strength and whirling resistance improve, but manufacturing complexity increases
Solution Approach 1:
The patent applies different fibre orientations locally within the composite shaft structure. Hoop-oriented fibres are placed in end regions where radial and torsional stresses are highest, while other regions use optimised winding angles for longitudinal strength. This local quality approach maximizes whirling resistance where needed without requiring complex manufacturing throughout the entire shaft.
Solution Approach 2:
The patent uses composite materials with tailored fibre orientations and material compositions to achieve high whirling resistance. By combining different fibre types and orientations in specific regions, the shaft achieves optimized performance characteristics without requiring overly complex manufacturing processes for the entire structure.
3Reliability
If mechanical splined interfaces are used for torque transfer, then reliability improves through verifiable load paths, but manufacturing precision requirements increase
Solution Approach 1:
The composite shaft material provides a consistent, uniform surface that facilitates precise spline interface manufacturing. The composite structure's inherent dimensional stability and surface uniformity enable tighter tolerances and more consistent mechanical interlocking compared to metallic shafts, thereby supporting the reliability benefits of verifiable load paths.
Data Source
AI summary
A fiber reinforced composite shaft bearing a metallic flanged end coupling (Fl) attached to the outside diameter through a concentric cylindrical torsional joint, comprising:a) a cylindrical end region comprising a wedge shaped inner layer of fiber (Hp) composite;b) a layer of outer helical composite plies (He) forming the shaft and extending over the wedge shaped inner layer, wherein the layer of outer helical plies has a tapered end part overlying wedge shaped inner layer to form the cylindrical end portion, wherein all helical plies of fibre layers are exposed on an outer surface; andc) a metallic flanged end coupling attached to the outer surface of the cylindrical end region through a primary mechanically interface (Sp) which may be splined.The joint may be strengthened by internally reinforcing the main shaft with an interference fit tubular plug (Pg) and protected from environmental degradation by inboard secondary adhesive bond (Ad).