Aircraft Window Fastening Bushing for Fatigue Reduction
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Solution Overview
Problem
Existing fastening assemblies for pressurized aircraft windows experience fatigue failure due to stress concentration around mounting holes caused by repeated pressurization, with previous solutions either lacking bushings or using deformable materials that exacerbate stress on the window.
Innovation Solution
A fastening assembly featuring an inner sleeve bushing made of relatively less rigid material and an outer sleeve bushing made of relatively rigid material, embedded in the mounting hole, which redistributes stress and minimizes damage by allowing minor movement of the window relative to the fuselage during pressurization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If no bushing is used with the fastener, then the device complexity is reduced, but the fasteners scratch the mounting hole surface leading to fatigue failure
Solution Approach 1:
The patent introduces a bushing assembly as an intermediary component between the fastener and the window mounting hole. This bushing prevents direct contact between the fastener and the mounting hole surface, eliminating scratching and fatigue failure while maintaining structural integrity.
2Reliability
If a rubber bushing is used with the fastener, then the mounting hole surface is protected from scratching, but the deformable rubber transmits excessive stress to the mounting hole causing fatigue failure
Solution Approach 1:
The patent changes the material parameter of the bushing from deformable rubber to rigid material with appropriate mechanical properties. This rigidity prevents excessive stress transmission to the mounting hole while still allowing the bushing to absorb minor movements and protect the mounting hole surface from scratching.
3Strength
If a single rigid bushing is used, then stress transmission is reduced, but the fastener cannot accommodate minor movements during pressurization
Solution Approach 1:
The patent segments the bushing into two distinct parts: an inner bushing made of rigid material to reduce stress transmission, and an outer bushing made of more compliant material to accommodate minor fastener movements during pressurization. This segmentation allows each component to fulfill its specific function optimally.
4Stress or pressure
If the bushing material is too rigid, then stress to the mounting hole is reduced, but the fastener cannot move minutely during pressurization
Solution Approach 1:
The patent applies local quality by using different material properties for different parts of the bushing assembly. The inner bushing uses rigid material locally at the stress concentration point to reduce mounting hole stress, while the outer bushing uses more compliant material locally to permit necessary fastener movement during pressurization cycles.
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 described fastening assembly significantly extends the life of the aircraft window by reducing maximum principal stress and fatigue failure, with the combination of aluminum for the inner sleeve bushing and steel for the outer sleeve bushing providing optimal results, allowing the window to move smoothly under tension loads while preventing damage.
Implementation Method 1
The inner sleeve bushing is formed from relatively less rigid material compared with material of the fastener and the outer sleeve bushing
Implementation Method 2
an outer sleeve bushing radially interposed between the inner sleeve bushing and the window... the outer sleeve bushing is formed from relatively rigid material compared with material of the window
Implementation Method 3
repeated tension loads work on the window according to repeated pressurization of the cabin of the aircraft... large fatigue load (stress) is caused around each mounting hole of the window
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A fastening assembly for a window of a pressurized fuselage of an aircraft includes a fastener received through a mounting hole defined in the window, an edge attachment member fixing the window to the fuselage, and a bushing assembly embedded in the mounting hole. The bushing assembly includes an inner sleeve bushing radially interposed between the fastener and the window and an outer sleeve bushing radially interposed between the inner sleeve bushing and the window. The inner sleeve bushing is formed from relatively less rigid metal compared with metal of the fastener and the outer sleeve bushing is formed from relatively rigid metal compared with material of the window and the metal of the inner sleeve bushing.