Radially Expanding Fastener for Sheet Joint Fatigue
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Solution Overview
Problem
Conventional fasteners used to join metal sheets, such as those in heavy construction or shipbuilding, fail to effectively counteract both axial and radial relative movements, leading to fatigue fractures and unthreading issues under alternating loads due to insufficient radial force absorption.
Innovation Solution
A joint system employing a mainly radially operating fastener with guide parts and expander sleeves that expand radially to fill gaps between sheets, combined with axially operating fasteners to secure the sheets, allowing for reduced hole diameters and accommodating alignment and thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional fasteners (nut and bolt arrangements or rivets) are used to join metal sheets, then axial forces can be transferred and sheets can be clamped, but radial forces cannot be effectively absorbed leading to fatigue fractures and unthreading
Solution Approach 1:
The fastener is divided into functionally distinct components: a guide part that provides axial clamping force, and one or more expander sleeves that independently absorb radial forces. This segmentation allows each component to specialize in counteracting specific force directions, thereby resolving the contradiction between axial force transfer and radial force absorption.
Solution Approach 2:
The expander sleeves are nested around the guide part within the recesses of the metal sheets. The sleeves can expand radially outward to engage the sheet walls while the guide part remains central, providing axial clamping. This nested configuration enables simultaneous axial and radial force management within a compact structure.
2Manufacturing precision
If holes in sheets are made with minimal clearance for the bolt, then precise alignment is achieved, but the bolt cannot accommodate alignment variations and thickness differences
Solution Approach 1:
The expander sleeves are designed to be dynamically adjustable in radial dimension. During installation, they can expand or contract radially to accommodate variations in hole diameter, alignment, and sheet thickness. Once installed, they expand to provide precise radial positioning, thus achieving both adaptability during installation and precision during operation.
Solution Approach 2:
The outer diameter of the expander sleeves can be changed during installation by expanding or contracting the sleeves radially. This parameter change allows the fastener to adapt to different hole sizes and alignment conditions. After installation, the sleeves maintain a fixed expanded state that provides precise positioning while having accommodated the initial variations.
3Reliability
If a mainly radially operating fastener with expander sleeves is used, then radial forces are absorbed and alignment variations are accommodated, but the device complexity increases
Solution Approach 1:
The guide part serves multiple functions: it provides axial clamping force through the nut and bolt arrangement, guides the expander sleeves during installation, and maintains central positioning within the recess. The expander sleeves simultaneously accommodate alignment variations during installation and provide radial force absorption during operation. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The expander sleeves are designed to automatically expand or contract radially during installation based on the actual hole dimensions and alignment conditions, without requiring external adjustment mechanisms. Once expanded, they self-lock within the recesses to provide both positioning and radial force absorption, eliminating the need for additional locking or adjustment components.
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 system effectively counteracts radial and axial movements, reducing the risk of fatigue fractures and unthreading, while adapting to different sheet thicknesses and hole configurations, providing a secure and durable connection.
Implementation Method 1
a clamping arrangement, arranged to provide an axial relative movement between the guide part and the expander sleeve, thus causing the expander sleeve to expand radially
Implementation Method 2
an expander sleeve, having an inner substantially conical surface, adapted to cooperate with the outer conical surface of the guide part
Implementation Method 3
Radial forces, counteracting relative movement between the sheets in a direction parallel with the planes of the sheets, are provided by the friction between the sheets and between the bolt head, nut and/or washer and its associated sheet
Data Source
Figure 1
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AI summary
There is provided a joint system for joining together at least two sheet portions, comprising a first sheet portion presenting a first recess, a second sheet portion, overlapping the first sheet portion, and presenting a second recess, the first and second recesses being substantially aligned; and a fastener received in said first and second recesses. The fastener is a mainly radially operating fastener.