Captive Composite End Joint With Curved Surfaces to Reduce Fretting
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Solution Overview
Problem
Joining composite structural components to metallic end fittings poses challenges due to fretting and wear, especially in aerospace applications, where a reliable and robust joint is required to transmit axial loads without complex manufacturing processes and adhesive bonding.
Innovation Solution
A captive mechanical joint design featuring an elongate member with a curved inner surface and an adjustable fastener, which transfers tension through a captive internal portion and compression through an external portion, minimizing frictional resistance and allowing for preloading to enhance strength-to-weight and strength-to-cost ratios without the need for bonding or complex manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical joint is used to join composite structural component to metallic end fitting, then reliable load transmission is achieved, but fretting and wear occur due to relative movement between the metal end fitting and the composite material
Solution Approach 1:
The end portion of the composite structural component is formed with a curved outer surface featuring a radius of curvature, creating a domed or rounded geometry. This curved surface interfaces with a corresponding curved inner surface of the end fitting, eliminating sharp edges and stress concentration points that would otherwise initiate fretting and wear. The curved contact surface distributes contact stresses more uniformly, reducing relative movement and wear between the metal end fitting and composite material during cyclic loading.
Solution Approach 2:
A fastening device is employed to apply a clamping force that preloads the joint before service loads are applied. This preliminary action creates frictional resistance and normal contact forces between the end fitting and composite component, establishing a stable contact condition that prevents relative movement and fretting during subsequent operational loading. The preloading ensures the joint maintains optimal contact pressure to eliminate wear.
2Reliability
If conventional mechanical joint design is used, then load transmission is achieved, but complex manufacturing capability is required to make a suitable mechanical joint
Solution Approach 1:
The invention changes the geometric parameters of the composite structural component by forming a curved end portion with a specific radius of curvature. This parameter change allows the use of standard, off-the-shelf end fittings with matching curved inner surfaces, eliminating the need for custom-machined complex geometries. The curved end portion can be manufactured using conventional composite fabrication processes such as filament winding or autoclave curing with a molded tooling surface, significantly simplifying manufacturing while maintaining joint strength.
3Stability of the object's composition
If frictional resistance is relied upon to prevent sliding between composite material member and end fitting, then joint stability is maintained, but damage and wear from fretting occur especially under cyclic loading
Solution Approach 1:
The curved outer surface of the composite structural component's end portion with a radius of curvature creates a distributed contact area with the end fitting, transforming concentrated contact stresses into distributed stresses. This curvature geometry reduces the tendency for relative sliding and fretting by ensuring uniform pressure distribution across the contact interface, thereby maintaining joint stability without the harmful effects of fretting wear under cyclic loading conditions.
4Weight of moving object
If metal end fitting with complex geometry is used to interface with composite structural component, then weight and cost efficiency is achieved, but sophisticated manufacturing capability is required
Solution Approach 1:
The invention adopts a curved end portion geometry with a defined radius of curvature that can be produced using standard composite manufacturing processes. This parameter choice allows the use of conventional, cost-effective fabrication methods such as filament winding with a curved mandrel or autoclave curing with a molded tooling surface, eliminating the need for sophisticated multi-step manufacturing processes while maintaining the weight efficiency of metal end fittings with matching curved inner surfaces.
Data Source
AI summary
A composite structural component comprises an elongate member made of a polymer matrix composite material. The elongate member comprises a main portion extending along an axis A and an end portion with an inner surface extending from the main portion to an open end of the member. The composite structural component also comprises an end fitting forming a mechanical joint with the end portion, the end fitting comprising an internal portion positioned captive within the elongate member in contact with the inner surface of the end portion; an external portion positioned in contact with an outer surface of the end portion; and an adjustable fastener extending axially between the internal and external portions to clamp the end portion between the internal and external portions. The inner surface of the end portion in contact with the internal portion extends towards the axis A at an increasing angle to the axis A.