Variable Taper Fastener Sleeve for Composite Delamination
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Solution Overview
Problem
The existing fastening technologies for aircraft structures, particularly those using composite materials, face challenges such as delamination risks due to friction during interference installation, and require a multitude of tools for varying thicknesses, leading to increased tooling costs and complexity in predicting structural strength.
Innovation Solution
A family of fasteners with variable taper, where the degree of taper is adjusted based on the height, allowing for a range of thickness configurations to be clamped using three or four sets of devices with the same outside diameter, without modifying the bore, and featuring a screw with a frustoconical shaft and a sleeve with a cylindrical outer surface and tapered inner surface, enabling interference installation to prevent delamination and reduce tooling needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interference installation is used to fill gaps in composite structures, then lightning resistance is improved, but delamination occurs due to friction
Solution Approach 1:
A cylindrical sleeve is introduced as an intermediary component between the conical screw and the composite structure. The sleeve has a cylindrical outer surface that fits into a cylindrical bore, and a conical inner surface that interfaces with the conical screw. This intermediary sleeve protects the composite material from direct friction during interference installation while still allowing the gap-filling function to be achieved.
Solution Approach 2:
The fastening system is segmented into three distinct components: a conical screw, a cylindrical-conical sleeve, and the composite structure. The sleeve acts as a separate protective layer that isolates the composite material from the friction-generating conical screw, thereby preventing delamination while maintaining the interference fit for gap filling.
2Manufacturing precision
If multiple tools are used for varying thickness configurations, then assembly precision is improved, but tooling cost and complexity increase
Solution Approach 1:
The conical screw with variable taper is designed to accommodate multiple thickness configurations through a single tool. By varying the degree of taper of the conical shaft, the same screw can be used for different element thicknesses, eliminating the need for multiple specialized tools while maintaining precise assembly for each configuration.
Solution Approach 2:
The degree of taper of the conical shaft is varied as a parameter to adapt the same screw design for different thickness configurations. This parameter change allows a single family of screws to cover multiple application scenarios, reducing tooling complexity while preserving assembly precision across different thicknesses.
3Reliability
If conical bores are machined for conical fasteners, then interference installation is enabled, but manufacturing difficulty increases
Solution Approach 1:
Instead of machining a conical bore to match the conical fastener, the approach is inverted: a simple cylindrical bore is machined, and a cylindrical-conical sleeve is inserted into it. The conical interface is created on the sleeve's inner surface, not on the bore itself, thereby simplifying the machining operation while still enabling interference installation.
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
This solution effectively prevents delamination in composite structures and allows for the assembly of various thickness configurations using a limited set of tools, enhancing the structural integrity and reducing tooling costs by allowing radial expansion of the sleeve to eliminate initial clearance, thus ensuring robust and efficient assembly.
Implementation Method 1
a radial expansion of this sleeve is required so that the play no longer exists
Data Source
Figure 1~2
Figure 3~4
AI summary
According to the prior art, there is a multiplicity of drilling and length families by fixation diameter recognition, contrarily to cylindrical smooth portion fixations for which a single tool is not sufficient. The person skilled in the art must plan the adequate tool and device for each thickness of a member to be clamped, which represents an important tool cost and also a time loss due to the change of tools. The purpose of the invention is to adapt the taper ratio (C1; C2) of the device (1, 20) based on the thickness to be clamped (12, 31). Preferably, the taper ratio of the bushings ranges between 1 and 4 %. Accordingly, using three to four reference sets of devices having the same outer diameter (16A, 16C) but a different taper ratio, it is possible to clamp any potential member thickness with modifying the bore diameter of members to be assembled.