Blind Fastener Geometry for Lower-Force Swaging and Fatigue Resistance
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Solution Overview
Problem
Existing blind fasteners often fail due to fatigue stresses and geometric variations in the bore, requiring high installation forces that can damage tools and structures, and lack sufficient corrosion resistance.
Innovation Solution
A blind fastener system comprising a sleeve and a mandrel with a specific geometry, where the mandrel has an enlarged portion and a pull region that allows for reduced installation force and enhanced corrosion resistance, allowing the sleeve to be deformed and swaged onto the mandrel without fracturing, using an installation tool to secure the fastener in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional blind fasteners are used, then fastening function is achieved, but high installation forces are required which can damage tools and structures
Solution Approach 1:
The patent modifies the geometric parameters of the mandrel, specifically the pull region length-to-diameter ratio (L/D ≤ 3.25) and the enlarged portion dimensions, to optimize the deformation characteristics during installation. These parameter changes enable the fastener to achieve proper deformation at lower installation forces, preventing damage to tools and surrounding structures while maintaining effective fastening
2Reliability
If conventional blind fasteners are used, then fastening is achieved, but fatigue stresses cause fastener failure
Solution Approach 1:
The patent optimizes the mandrel geometry parameters, particularly the pull region L/D ratio and the enlarged portion dimensions, to distribute stresses more evenly during installation and service. This reduces stress concentration points that would otherwise lead to fatigue failure, thereby improving fastener durability and reliability without compromising strength
Solution Approach 2:
The enlarged portion of the mandrel acts as a stress-distributing element that prevents excessive stress concentration during installation. By designing this feature in advance, the fastener is cushioned against the high stresses that would otherwise lead to immediate or fatigue failure, enhancing overall reliability
3Adaptability or versatility
If conventional blind fasteners are used, then fastening is achieved, but geometric variations in the bore cause installation problems
Solution Approach 1:
The patent designs the mandrel with specific geometric parameters, including the pull region L/D ratio and the enlarged portion dimensions, that provide a tolerance buffer against bore variations. These parameter optimizations allow the fastener to accommodate geometric variations in the bore while still achieving proper deformation and secure installation, reducing sensitivity to manufacturing precision requirements
4Reliability
If conventional blind fasteners are used, then fastening is achieved, but corrosion resistance is insufficient
Solution Approach 1:
The patent employs composite material construction, combining a corrosion-resistant outer sleeve with a mandrel that may be made of different materials. This composite approach allows the sleeve to provide superior corrosion protection while the mandrel provides structural function, achieving enhanced overall corrosion resistance through material combination rather than relying on a single material solution
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 reduces installation forces, extends tool life, minimizes structural damage, enhances ergonomics, and improves corrosion resistance, enabling lighter tools and more efficient fastening processes.
Implementation Method 1
The portion of the sleeve on a first side of the structure is deformed, and the second sleeve end is swaged onto the shank region of the mandrel on an oppositely disposed second side of the structure
Implementation Method 2
the pull region is moved distal from the second sleeve end utilizing the collet of the installation tool
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present disclosure relates to a blind fastener and a method of installation thereof. The blind fastener comprises a sleeve and a mandrel. The sleeve comprises a first sleeve end, a second sleeve end, and a cavity extending from the first sleeve end to the second sleeve end. The mandrel is configured to be at least partially received by the cavity of the sleeve. The mandrel comprises a first mandrel end disposed adjacent to the first sleeve end and comprising an enlarged portion having a diameter greater than a diameter of the cavity, a second mandrel end comprising a pull region, and a shank region extending intermediate the first mandrel end and the second mandrel end. The pull region comprises an axial length no greater than four times a diameter of the shank region and is configured to be engaged by an installation tool.