Frangible Interlayer Fastener Assembly Against Jam Nut Effects
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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 over-torquing and 'jam nut effects' that lead to inconsistencies and material deformation.
Innovation Solution
A fastener assembly with a bolt and nut member, featuring a drive element joined via an interlayer structure that fractures in torsional shear, preventing over-torquing and eliminating 'jam nut effects by using materials with different shear moduli and joining methods like brazing or soldering, ensuring controlled torque application and consistent installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional fastener assemblies are used in aerospace applications, then they can be installed in threaded blind holes, but they are prone to over-torquing and jam nut effects that cause material deformation and inconsistent installation
Solution Approach 1:
The fastener assembly is segmented into distinct components: a fastener member (bolt or screw) and a separate drive element. The drive element includes a drive interface for tool engagement and a frangible portion that connects it to the fastener member. This segmentation allows the drive element to function as a disposable torque-limiting device, ensuring consistent installation without compromising the reliability of the fastener itself.
Solution Approach 2:
The drive element is designed as a disposable component with a frangible portion that is intended to fail after a single use. This frangible portion has controlled weakness that causes it to break when a predetermined torque is applied, preventing over-torquing. The disposable nature of the drive element ensures that each fastener installation has a fresh, uncontaminated torque application mechanism, thereby ensuring installation consistency and reliability.
2Strength
If high torque is applied to secure fasteners in aerospace applications, then fastener strength is improved, but material deformation and jam nut effects occur
Solution Approach 1:
The frangible portion in the drive element is designed with controlled weakness that creates a predetermined torque limit before the fastener can be over-torqued. This preliminary anti-action mechanism prevents the application of excessive torque that would cause material deformation or jam nut effects. The frangible portion breaks at a specific torque threshold, thereby protecting the workpiece and fastener from harmful forces while still providing sufficient clamping force for secure fastening.
3Device complexity
If drive elements are directly joined to fasteners, then assembly simplicity is improved, but torque control precision deteriorates due to jam nut effects
Solution Approach 1:
The drive element serves as an intermediary component between the installation tool and the fastener member. It includes a drive interface that engages with the installation tool and a frangible portion that connects to the fastener member. This intermediary structure provides a controlled interface for torque application, with the frangible portion acting as a torque-limiting mechanism. The drive element's design ensures precise torque control by preventing direct engagement between the tool and fastener, thereby eliminating jam nut effects while maintaining reasonable assembly simplicity.
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 provides reliable and consistent installation performance, preventing material deformation and ensuring the fastener assembly maintains integrity, with precise torque control and reduced risk of premature failure, enhancing the reliability and durability of the fastener assembly.
Implementation Method 1
The first surface of the interlayer structure is at least partly joined to the member of the fastener assembly to which the drive element is joined by means of a material-locking joint
Implementation Method 2
The second surface of the interlayer structure is at least partly joined to the body of the drive element by means of a material-locking joint
Implementation Method 3
the interlayer structure has a first surface facing an end of the member of the fastener assembly to which the drive element is joined, and a second surface facing an end of the body of the drive element, wherein the first surface of the interlayer structure is at least partly joined to the member
Implementation Method 4
The shank of the bolt member may include a threaded portion having a plurality of external bolt threads, the bolt threads of the bolt being defined by a plurality of crests and a plurality of roots
Data Source
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AI summary
The invention relates to a fastener assembly (100) comprising at least one of a bolt member (15) and a nut member (40); and a drive element (20) adapted for engagement by an installation/driving tool, said drive element (20) comprising a body (21). The body (21) of the drive element (20) is joined either to the bolt member (15) or to the nut member (40) by means of an interposed interlayer structure (5), the interlayer structure (5) being adapted to fracture in torsional shear and/or tensile stress in response to a relative rotational and/or tensile force applied to the drive element (20) with the installation/driving tool.