Sleeved Interference Fastener for Composite Structures
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing aerospace fasteners are unsafe for interference conditions in graphite or mixed composite-metallic structures, leading to structural concerns, delamination, and ineffective dissipation of lightning and electromagnetic currents, and are limited in application and sealant usage.
Innovation Solution
A sleeved interference fastener with a pin member featuring a smooth cylindrical shank, threaded portion, and frangible section, along with a sleeve that radially expands for interference fit, minimizing installation force and allowing for secure clamping and electrical conductivity across various structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clearance fit fasteners are utilized to avoid composite delamination and structural failure, then structural safety is improved, but dynamic joint performance is reduced and gaps remain in the structure
Solution Approach 1:
The fastener is divided into two functional components: a pin member that provides mechanical fastening and a separate sleeve member that provides interference fit and electrical conductivity. This segmentation allows each component to optimize its function without compromising the other, enabling both structural safety and dynamic joint performance.
Solution Approach 2:
The sleeve member acts as an intermediary between the pin member and the composite structure. It provides the interference fit to eliminate gaps while the pin member provides mechanical fastening, and together they ensure both structural safety and electrical conductivity for lightning strike dissipation.
2Productivity
If interference fit fasteners are installed in graphite composite structures, then dynamic joint performance is improved and gaps are eliminated, but composite delamination and structural failure occur
Solution Approach 1:
By separating the interference fit function (sleeve) from the mechanical fastening function (pin), the system achieves high dynamic joint performance without subjecting the composite structure to excessive installation forces that would cause delamination.
Solution Approach 2:
The sleeve member is designed with specific material properties and geometric parameters (interference fit tolerance, wall thickness) that allow it to achieve the desired interference fit without exceeding the composite structure's strength limits, thus maintaining structural safety.
3Reliability
If significant amounts of sealant are utilized during fastener installation, then sealing is improved, but coefficient of friction is reduced and installation capability is hindered
Solution Approach 1:
The sealant application is extracted from the fastener installation process itself. The sleeve member is first installed in the clearance hole with sealant applied to ensure sealing, then the pin member is installed separately through the sleeve without requiring sealant, thus maintaining high installation capability while ensuring proper sealing.
4Adaptability or versatility
If previous pins with mating sleeves are manufactured for interference applications, then installation in 100% graphite composite is achieved, but application versatility is limited to short lengths and small diameters
Solution Approach 1:
The pin-sleeve fastener system is designed with universal applicability across different composite and metallic structures. The modular design allows the same basic fastener type to be used in various applications including short and long lengths, small and large diameters, and different material compositions, greatly expanding application versatility while maintaining installation safety.
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 fastener provides safe and cost-effective dissipation of electrical currents, eliminates gaps for improved structural integrity, and supports a wide range of applications without delamination or structural failure, enhancing dynamic joint performance and safety.
Implementation Method 1
The friction between the outer surface of the sleeve and the inner diameter surface of the holes is greater than the friction between the inner surface of the sleeve and the smooth cylindrical shank of the pin member
Implementation Method 2
The frangible portion includes a breakneck groove between the threaded portion and the pull groove portion. As the fastener is installed, the frangible portion is separated at the breakneck groove
Implementation Method 3
The friction between the outer surface of the sleeve and the inner diameter surface of the holes is greater than the friction between the inner surface of the sleeve and the smooth cylindrical shank of the pin member, allowing the sleeve to expand radially upon insertion
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A fastener adapted to pass through aligned holes through workpieces is disclosed. The fastener includes a pin member (15) having a transition portion (55) wherein the diameter of the transition portion decreases radially as it extends from the smooth cylindrical shank portion (45) to the threaded portion (50). The fastener may also comprise a sleeve member (20) and a clamping means. The clamping means includes a collar (200), a nut, or any other possible clamping means. In exemplary embodiments, the workpieces can be formed with a plurality of materials, the materials including composite, metallic, or composite/metallic structures, any combination thereof. In particular embodiments, the fastener has interference capability of 0,013 to 0,25 mm (0.0005 to 0.0100 inches) in composite structures without risk of composite delamination or damage. As a result of the fastener interference, gaps between the fastener and the structure are eliminated thereby providing good electrical conductivity between components. As a result, the potential for electrical sparks is reduced, providing a safer fastener for use with aerospace applications.