Frangible Drive Fastener Assembly for Precise Torque Control
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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 and nut member with interlayer structures that fracture in 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 shear and consistent installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional deformable drive nuts are used to apply torque to fasteners, then installation can be performed, but jam nut effects occur leading to inconsistent installation loads and material deformation
Solution Approach 1:
The drive element is designed as a disposable component that is intentionally weakened at specific points (frangible portions) to fracture during installation. This allows the drive element to be used once to apply precise torque and then discarded, eliminating the need for complex reusable mechanisms that cause jam nut effects.
Solution Approach 2:
The drive element incorporates frangible portions with controlled geometric parameters (reduced cross-sectional area, material properties) that cause them to fracture at predetermined torque levels. This parameter change allows precise control of installation loads without the inconsistencies associated with deformable drive nuts.
2Reliability
If high torque is applied to ensure fastener security in aerospace applications, then fastener reliability improves, but over-torquing causes material deformation and fastener damage
Solution Approach 1:
The frangible portions are pre-designed with predetermined fracture torques that are calibrated to occur before over-torquing can damage the fastener or workpiece. This preliminary design feature automatically limits the maximum torque applied, ensuring fastener security without material damage.
Solution Approach 2:
The fracture of the frangible portion provides immediate feedback that the predetermined torque has been reached. This visual and mechanical feedback mechanism ensures that the installer stops applying torque at the correct point, preventing over-torquing while ensuring adequate fastener security.
3Ease of operation
If drive elements are made deformable to facilitate installation, then ease of installation improves, but inconsistent installation loads and jam nut effects occur
Solution Approach 1:
The drive element is segmented into a main body and frangible portions with distinct functions. The main body provides the driving interface and structural integrity, while the frangible portions provide controlled weakness for predictable fracture. This segmentation allows the drive element to be easy to install while maintaining consistent installation loads.
Solution Approach 2:
The frangible portions act as intermediaries between the drive element body and the fastener. They transmit the installation torque from the drive tool to the fastener while being designed to fracture at a predetermined point, thereby mediating the torque transmission to prevent both under-torquing and over-torquing.
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 precise torque application and maintaining structural integrity under varying loads, thus addressing the need for enduring strength and reliability in aerospace environments.
Implementation Method 1
the interlayer structure is adapted to fracture in torsional shear or tensile stress in response to a relative rotational or tensile force applied to the drive element
Implementation Method 2
the interlayer structure is adapted to fracture in torsional shear or tensile stress in response to a relative rotational or tensile force applied to the drive element
Data Source
Figure 1~2
AI summary
The invention relates to a fastener assembly (100) comprising : a bolt member (15) having first and second ends and comprising a bolt head (17) at the first end and a shank (16), at least a part of which is screw threaded; a nut member (40) for screw threaded engagement with the shank (16) of the bolt member (17); and a first drive element (20.1) allocated to the bolt member (15) and a second drive element (20.2) allocated to the nut member (40), said first and second drive elements (20.1, 20.2) each comprising a body (21.1, 21.2) and being adapted for engagement by a corresponding installation/driving tool. The body (21.1) of the first drive element (20.1) is joined to the bolt member (15) by means of a first interposed interlayer structure (5.1) and the body (21.2) of the second drive element (20.2) is joined to the nut member (40) by means of a second interposed interlayer structure (5.2). The first interlayer structure (5.1) is adapted to fracture in torsional shear and/or tensile stress in response to a first relative rotational and/or tensile force applied to the first drive element (20.1), and the second interlayer structure (5.2) is adapted to fracture in torsional shear and/or tensile stress in response to a second relative rotational and/or tensile force applied to the second drive element (20.2).