Blind Fastener Sleeve Lock for Flush Composite Installation
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Solution Overview
Problem
Conventional blind fasteners often cause damage to composite laminates due to inadequate bearing load distribution, leading to delamination and requiring secondary operations for aerodynamic flushness, and they are heavy and prone to inconsistent break-off tolerances.
Innovation Solution
A blind fastener design with a reduced length and weight, featuring a titanium nut and bolt with a positive mechanical lock, a consistent break-off mechanism, and a design that eliminates the need for secondary operations by ensuring a flush break-off and consistent blind side upset, utilizing a nut with three recesses and a sleeve with a crimped portion to maintain preload and prevent disassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional blind fasteners are used, then they can provide basic fastening function, but they cause damage to composite laminates due to inadequate bearing load distribution
Solution Approach 1:
The fastener system is segmented into multiple functional components: a blind fastener body, a separate sleeve, and a break-off mechanism. The sleeve acts as an independent load-distributing element that spreads bearing loads over a larger area of the composite laminate, preventing delamination while maintaining fastening strength.
Solution Approach 2:
The invention uses composite material construction for the fastener components, particularly combining different metal materials (such as aluminum alloy fastener body with steel sleeve) to optimize both strength and weight. The composite structure allows each material to contribute its superior properties to the overall fastening system.
2Manufacturing precision
If conventional blind fasteners are used, then they can secure fastening, but they require secondary operations for aerodynamic flushness
Solution Approach 1:
The fastener incorporates a pre-designed break-off mechanism with a predetermined break point that ensures automatic flush break-off during installation. The sleeve and fastener body are designed with specific geometric features that guarantee a clean, flush break surface, eliminating the need for subsequent shaving, milling, or grinding operations to achieve aerodynamic flushness.
3Weight of moving object
If conventional blind fasteners are used, then they can provide fastening function, but they are heavy
Solution Approach 1:
The invention optimizes the physical parameters of the fastener components, including reducing material density by selecting lightweight alloys, minimizing cross-sectional dimensions while maintaining strength, and optimizing the length-to-diameter ratio. The sleeve thickness and fastener body geometry are carefully parameterized to achieve the lightest possible weight that still satisfies all strength and load-bearing requirements.
4Manufacturing precision
If conventional blind fasteners are used, then they can be installed, but they are prone to inconsistent break-off tolerances
Solution Approach 1:
The fastener incorporates a self-regulating break-off mechanism where the sleeve and fastener body automatically control the break-off process. The predetermined break point geometry and material properties ensure that the break occurs consistently at the designed location regardless of installation variations, providing self-service quality control that eliminates the need for post-installation adjustments or rework.
Data Source
AI summary
Disclosed is a fastener that includes a nut with a threaded bore that includes a head on one end having three recesses, a cylindrical outer surface and a tapered ramp on the other end, a bolt that includes a head, a threaded portion engaged with the threaded bore, a recess next to the bolt head and an enlarged shank between the threads and the recess, where the outer diameter of the recess is smaller than a major diameter of the threaded bore of the nut and where an outer diameter of the shank is larger than a major diameter of the bolt threads, and a sleeve with a unthreaded bore positioned between the tapered ramp and the bolt head with one end crimped into the recess such that the internal diameter of the crimped sleeve bore is smaller than the major diameter of the threads on the bolt.