Interference-Fit Fastener With Sacrificial Lubricating Ring
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Solution Overview
Problem
Interference-fitted fasteners face challenges in multi-layer aircraft structures due to the 'staircase effect' of varying material rigidity, leading to increased insertion forces and potential damage, especially when transitioning from composite to metal layers, and the lubricant/coating deterioration during assembly.
Innovation Solution
A fastener with a sacrificial ring containing an oil-based lubricant, encapsulated in a polymer resin matrix, is used. The ring is designed to wear down and release lubricant during insertion, reducing friction and wear, and is positioned on the shank and transition zone to facilitate smooth interference fitting across different material layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If interference-fitted fasteners are used in multi-layer aircraft structures, then the strength and cyclic load resistance of the structure is improved, but the insertion force increases and damage may occur during assembly
Solution Approach 1:
A sacrificial ring made of soft material (e.g., lead, tin, aluminum) is introduced as an intermediary element between the fastener shank and the aperture wall. This ring deforms plastically during insertion, absorbing the high insertion forces and preventing direct contact between the fastener and the rigid aperture wall, thereby reducing the risk of damage while maintaining the interference fit's structural benefits
Solution Approach 2:
The sacrificial ring is pre-installed on the fastener shank before insertion into the aperture. This ring acts as a cushioning element that deforms during the interference fitting process, absorbing the impact and friction forces that would otherwise be transmitted directly to the fastener and aperture, thus preventing damage before it occurs
2Length of moving object
If the fastener is forcibly inserted into hard material layers like titanium, then complete insertion is achieved, but the lubricant coating deteriorates and friction increases
Solution Approach 1:
The sacrificial ring is designed as a consumable, low-cost component that is deliberately depleted during the insertion process. As the ring deforms and wears away, it continuously releases lubricant onto the fastener shank and aperture wall, ensuring sustained lubrication throughout the insertion process even in hard material layers where coating deterioration would normally occur
3Ease of operation
If the sacrificial ring is made to wear down during insertion, then friction and wear are reduced, but the ring material is consumed
Solution Approach 1:
The potential harm of material consumption is converted into a benefit: the sacrificial ring's deliberate wear and depletion during insertion continuously releases lubricant, reducing friction and wear on the critical fastener and aperture surfaces. The ring's material loss is the mechanism by which lubrication is maintained, transforming what would normally be a negative (material consumption) into a positive (friction reduction)
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 sacrificial ring significantly reduces the insertion force required, prevents damage to the fastener and structure, and maintains lubrication throughout the assembly process, enabling complete insertion even in thick or multi-layered structures with hard materials like titanium.
Implementation Method 1
A fastener (10) according to one embodiment of the invention... comprises a lubricating sacrificial ring (20). The ring (20) is worn through interference with an interior wall of the aperture (8)... so as to release a lubricating substance between a distal end of the smooth shank (14) and a proximal end of the smooth shank
Implementation Method 2
the lubricating sacrificial ring (20) is worn through interference with an interior wall of the aperture (8)... so as to release a lubricating substance... reducing friction and wear
Data Source
Figure 1~3
Figure 4~4E
Figure 5~6
AI summary
The invention relates to a fastener for assembling at least two structural elements, comprising a aperture, the fastener comprising an enlarged head (12) and a shank (14) exhibiting, prior to fitting, an outside diameter (D ) greater than an inside diameter (D S ) of the aperture, and a locking portion comprising a screw thread or annular grooves. The fastener further comprises a lubricating sacrificial ring (40) on the exterior surface of the fastener, extending at least between a distal end of the shank and a proximal end of the locking portion, said ring having, before the fastener is fitted into the structure, an outside diameter greater than a diameter of the aperture. The sacrificial ring comprises a polymer resin forming a matrix encapsulating dispersant molecules and oil molecules. The invention applies to the assembly of aircraft structures.