Sacrificial Lubricating Ring for Interference-Fit Fastener Assembly
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Solution Overview
Problem
Interference-fitted fasteners face challenges in multi-layered aircraft structures due to the 'staircase effect' of varying material rigidity and coating deterioration, leading to increased insertion forces and potential damage during assembly.
Innovation Solution
A fastener with a sacrificial ring having a toroidal shape, positioned on the exterior surface, which wears down to release lubricant and reduce friction, ensuring reliable insertion by distributing lubricant between the fastener and structure, thereby reducing insertion forces and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If interference-fitted fasteners are used in multi-layered aircraft structures, then the strength and ability to withstand cyclic loadings are improved, but the insertion forces increase and damage may occur during assembly
Solution Approach 1:
A sacrificial ring is introduced as an intermediary element between the fastener and the multi-layered structure. This ring wears down during insertion, releasing lubricant that reduces friction and insertion forces. The ring acts as a mediator that protects the fastener and structure during the interference fitting process, enabling successful installation without damage while maintaining the strength benefits of interference fitting.
Solution Approach 2:
The friction characteristics between the fastener and structure are changed by introducing a lubricant through the sacrificial ring. The lubricant modifies the interface parameters (coefficient of friction) during insertion, reducing the insertion forces required. This parameter change allows the interference fit to be achieved with acceptable installation forces while maintaining the final joint strength.
2Strength
If interference-fitted fasteners are used in multi-layered aircraft structures, then the strength and ability to withstand cyclic loadings are improved, but the coating deteriorates and friction increases during assembly
Solution Approach 1:
The sacrificial ring serves as a protective intermediary that prevents direct contact and friction between the fastener coating and the structure. By wearing down instead, the ring shields the coating on both the fastener and structure from deterioration, maintaining the protective coating integrity while still enabling the interference fit to be achieved.
Solution Approach 2:
The sacrificial ring is designed as a consumable, short-lived component that is sacrificed during the insertion process. It is replaced or worn down to protect the more valuable and permanent components (fastener and structure coatings) from damage. The ring's temporary existence enables the installation process without compromising the long-term integrity of the coated surfaces.
3Force
If lubricant is applied to reduce friction during insertion, then the insertion forces are reduced, but the lubricant may be insufficient in thick or multi-layered structures
Solution Approach 1:
The lubricant is pre-loaded within the sacrificial ring structure before insertion. As the ring wears down during the insertion process, the lubricant is progressively released along the path of the fastener. This preliminary positioning of the lubricant source ensures continuous lubrication throughout the insertion process, particularly in thick or multi-layered structures where the insertion distance is long and external lubrication would be insufficient.
Solution Approach 2:
The sacrificial ring automatically releases lubricant during the insertion process based on its own wear and compression. The system is self-regulating, providing lubricant as needed without external intervention. The ring's mechanical deformation during insertion naturally dispenses the lubricant along the fastener path, ensuring adequate lubrication is maintained throughout the entire insertion process in structures of any thickness.
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 effectively reduces the forces required for insertion, ensures complete fastener integration, and maintains lubrication, even in thick or multi-layered structures with varying material rigidity, preventing damage and ensuring reliable assembly.
Implementation Method 1
the sacrificial ring is worn through interference with an interior wall of the aperture or of the sleeve, so as to release a lubricating substance between a distal end of the smooth shank and a proximal end of the smooth shank
Data Source
AI summary
A fastener for assembling at least two structural elements having an aperture, may have a fastener comprising an enlarged head (12) and a shank (14) exhibiting, prior to fitting, an outside diameter (D1) greater than an inside diameter (DS) 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 fastener assembly may apply to the assembly of aircraft structures.