Frangible Drive Fastener Assembly for Controlled Torque Shearing
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Solution Overview
Problem
Existing fastener assemblies face challenges in aerospace applications due to vibrations and sonic fatigue, requiring fasteners of enduring strength and reliability, while also avoiding issues like 'jam nut effects' that lead to inconsistent installation loads and material deformation.
Innovation Solution
The fastener assembly incorporates a bolt member with a threaded shank and a nut member, both connected via interlayer structures that fracture under torsional shear or tensile stress, preventing over-torquing and eliminating 'jam nut effects by using non-deformable drive elements and materials with different shear moduli, ensuring controlled shearing and consistent installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional deformable drive elements are used, then installation flexibility is improved, but inconsistent installation loads and over-torquing occur due to jam nut effects
Solution Approach 1:
The drive element is designed as a disposable component that fractures at a predetermined location during installation. This frangible drive element prevents over-torquing by breaking when a maximum torque threshold is reached, ensuring consistent installation loads while maintaining installation flexibility through its deformable design before fracture.
Solution Approach 2:
The drive element is pre-designed with a frangible portion at a specific location that will fracture at a predetermined torque level. This preliminary design ensures that the installation process automatically stops at the correct torque without requiring additional control mechanisms, preventing over-torquing before it can cause damage.
2Reliability
If high-strength materials are used to resist vibrations and sonic fatigue, then reliability under dynamic loads is improved, but susceptibility to over-torquing increases
Solution Approach 1:
The frangible drive element acts as an intermediary protective component between the installation tool and the high-strength fastener. It absorbs the harmful over-torquing forces through controlled fracture, protecting the high-strength fastener and workpiece while allowing the fastener to maintain its vibration and sonic fatigue resistance properties.
Solution Approach 2:
The drive element is designed as a sacrificial component that fractures at a predetermined torque level. This disposable element protects the more expensive high-strength fastener from over-torquing damage, allowing the fastener to maintain its full strength properties for resisting vibrations and sonic fatigue during service.
3Strength
If material-locking joints are used to ensure strong connections, then joint strength is improved, but difficulty in controlled shearing increases
Solution Approach 1:
The drive element is designed with non-uniform geometry, featuring a frangible portion with reduced cross-sectional area at a specific location. This local quality variation creates a predetermined weak point that will fracture first during installation, enabling controlled shearing while the rest of the drive element and fastener maintain strong material-locking joints.
Solution Approach 2:
The drive element is segmented into different portions with different structural properties: a frangible portion with reduced strength for controlled fracture, and stronger portions for maintaining connection integrity. This segmentation allows the joint to have overall high strength while enabling controlled shearing at the frangible portion during installation.
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
This design enhances the reliability and consistency of fastener assemblies by preventing over-torquing and material deformation, ensuring controlled shearing and maintaining structural integrity, even under varying loads and environmental conditions.
Implementation Method 1
The first interlayer structure is adapted to fracture in torsional shear in response to a first relative rotational force applied to the first drive element
Implementation Method 2
The first interlayer structure is adapted to fracture in tensile stress in response to a first relative tensile force applied to the first drive element
Data Source
AI summary
Disclosed is a fastener assembly comprising: a bolt member, comprising a bolt head and a shank, at least a part of which is screw threaded; a nut member for threaded engagement with the shank; a first drive element allocated to the bolt member and a second drive element allocated to the nut member, each drive element comprising a body and adapted for engagement by a corresponding tool. The body of the first drive element is joined to the bolt member by a first interposed interlayer structure. The body of the second drive element is joined to the nut member by a second interposed interlayer structure. The first interlayer structure is adapted to fracture in response to relative rotational and/or tensile force applied to the first drive element. The second interlayer structure is adapted to fracture in response to relative rotational and/or tensile force applied to the second drive element.