Tubular Fusible Member Hinge Design for Predictable Shear Rupture
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Solution Overview
Problem
The existing fusible members in aircraft landing gear connections face challenges in reconciling fatigue strength and rupture threshold constraints, leading to limited fatigue strength and frequent replacement due to difficulty in designing a member that can withstand normal operations without premature rupture under excessive forces.
Innovation Solution
A tubular fusible member with a varying cross-section, featuring reinforced thickness in distal sections and a higher second moment of area in the central section, designed to rupture in shear between the central and distal portions when subjected to forces exceeding a threshold, while maintaining sufficient bending strength and fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the fusible member is designed with sufficient mechanical strength to withstand normal operations, then fatigue strength is improved, but the member fails to rupture in predictable manner when load exceeds threshold
Solution Approach 1:
The fusible member features a non-uniform cross-sectional area along its length, with a reduced section (waist) having smaller area than the end sections. This local variation creates a predetermined weak point that will rupture first under excessive load, ensuring predictable failure mode while maintaining sufficient strength in other regions to withstand normal operations and provide adequate fatigue life.
Solution Approach 2:
The fusible member is divided into distinct sections with different cross-sectional areas: end sections with larger area for strength and fatigue resistance, and a central reduced section for controlled rupture. This segmentation allows different parts of the same component to serve different functions - the stronger end sections handle normal operational stresses while the weaker central section acts as a fuse.
2Reliability
If the fusible member is designed with limited fatigue strength to enable rupture above threshold, then rupture threshold is achieved, but the member requires frequent replacement
Solution Approach 1:
By concentrating the weakness in a specific localized region (the reduced central section) rather than uniformly reducing strength throughout, the design allows the majority of the member to maintain high fatigue strength. This enables the member to withstand many operational cycles before the predetermined rupture point is reached, extending service life while maintaining the rupture threshold function.
3Ease of manufacture
If the fusible member has uniform cross-section, then manufacturing is simplified, but it cannot simultaneously satisfy fatigue strength and rupture threshold constraints
Solution Approach 1:
The non-uniform cross-section is implemented through a single, continuous forming process that creates the varied profile in one operation. This approach maintains manufacturing simplicity while achieving the complex performance requirements, avoiding the need for multiple assembly steps or complex multi-component construction.
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 solution effectively reconciles fatigue strength and rupture threshold constraints, reducing premature fatigue rupture and extending the lifespan of the fusible member by strategically distributing thickness and second moment of area along its length, ensuring reliable operation under varying loads.
Implementation Method 1
the fusible member rupturing in shear between its central portion and each distal portion when the service forces have a magnitude along an axis perpendicular to the longitudinal axis that is greater than a predetermined threshold value
Implementation Method 2
the fusible member being stressed in bending when the hinge is in a service position, the member being subjected to service forces in a predetermined direction relative to the clevis to which the fusible member is constrained in rotation
Implementation Method 3
the member must have sufficient mechanical strength to enable it to withstand a certain number of landings without rupturing, i.e. it must have appropriate fatigue strength
Data Source
AI summary
The invention relates to a tubular fusible member (21) extending along a longitudinal axis (AL) and for engaging in a two-lug clevis (14) and a single-lug clevis (12) in order to form a hinge (11). According to the invention, the fusible member (21) is constrained in rotation with one of the clevises (12, 14), and it presents a cross-section of shape that varies gradually between a central section and two distal sections, each distal section having reinforced thickness in its regions that extend parallel to the bending plane (PF) in which the fusible member (21) bends when it is stressed, the central section having a second moment of area relative to an axis normal to the bending plane (PF) that is greater than the second moment of area of the distal sections.