Blind Fastener Insert for Lightning Current Transfer in Composites
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Solution Overview
Problem
Carbon fiber reinforced composite aircraft structures are vulnerable to lightning strikes due to their low electrical conductivity, and metallic fasteners can create detrimental ignition sources and physical damage when lightning currents arc between them and the composite structure.
Innovation Solution
A blind fastener system comprising a sleeve, a core bolt, and an insert, where the insert is configured to provide an electrically conductive path between the sleeve and the core bolt, reducing contact resistance and facilitating the transfer of lightning currents with minimal adverse effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallic fasteners are used to secure carbon fiber reinforced composite workpieces, then mechanical strength and structural integrity are improved, but electrical conductivity increases creating ignition sources and physical damage during lightning strikes
Solution Approach 1:
The patent introduces an electrically conductive insert as an intermediary component between the metallic core bolt and the carbon fiber reinforced composite sleeve. This insert serves as a mediator that provides a controlled electrical pathway, allowing lightning currents to pass through the fastener assembly without creating harmful arcing or ignition sources. The insert material (such as copper or aluminum) has high electrical conductivity that bridges the gap between the metallic bolt and composite sleeve, resolving the contradiction by enabling both mechanical strength and lightning strike management.
Solution Approach 2:
The fastener assembly employs a composite structure combining multiple materials: a metallic core bolt for mechanical strength, an electrically conductive insert for electrical conductivity, and a carbon fiber reinforced composite sleeve for structural integration. This multi-material composite approach allows each component to fulfill its specific function - the metallic bolt provides tensile strength, the insert provides electrical pathways, and the composite sleeve provides structural integration with the airframe - thereby resolving the contradiction between mechanical strength and lightning strike vulnerability.
2Weight of moving object
If carbon fiber reinforced composites are used for aircraft structures, then weight-to-strength ratio is improved, but electrical conductivity decreases leading to lightning strike susceptibility
Solution Approach 1:
The electrically conductive insert acts as an intermediary that compensates for the low electrical conductivity of carbon fiber reinforced composites. By embedding this conductive element within the fastener assembly, the system creates dedicated electrical pathways that bypass the inherently resistive composite material, allowing lightning currents to flow safely through the fastener without causing damage to the composite structure.
Solution Approach 2:
The patent applies local quality by concentrating electrical conductivity specifically at the fastener locations where lightning currents need to be channeled. Rather than making the entire composite structure electrically conductive (which would add weight), the conductive insert provides localized electrical pathways at critical joint locations, enabling the composite airframe to maintain its lightweight properties while being protected against lightning strikes at fastener interfaces.
3Ease of operation
If blind fasteners are used for limited access applications, then ease of installation is improved, but electrical contact resistance increases creating ignition sources
Solution Approach 1:
The electrically conductive insert serves as a mediator that ensures low electrical contact resistance in blind fastener applications where only one side is accessible. The insert is positioned within the sleeve and makes contact with both the core bolt and the composite sleeve, creating reliable electrical pathways without requiring access to both sides of the joint for installation or adjustment.
Solution Approach 2:
The fastener assembly is designed to self-establish electrical contact through the conductive insert during the normal installation process. As the core bolt is inserted and tightened through the sleeve, the insert automatically makes contact with both components, creating the electrical pathway without requiring additional operations or access to the blind side of the joint. This self-service mechanism enables both easy installation and lightning strike protection in limited access applications.
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 blind fastener system effectively manages lightning currents by providing a low-resistance electrical path, reducing the risk of ignition and physical damage to the fasteners and composite structure, thereby enhancing the structural integrity and safety of carbon fiber reinforced composite aircraft.
Implementation Method 1
the insert is configured to provide an electrically conductive path between the sleeve and the core bolt, reducing contact resistance and facilitating the transfer of lightning currents
Data Source
AI summary
A fastener includes a sleeve, a core bolt and an insert. The sleeve includes a tubular portion and an internal thread. The core bolt includes a cylindrical portion, a threaded portion with an external thread, and a thread runout between the cylindrical portion and the threaded portion. The core bolt is disposed within the sleeve and the external thread engages the internal thread. The insert is disposed within the sleeve and encircles a portion of the core bolt. The insert abuts and is retained between the internal thread and the thread runout in a pre-installation position. The insert is compressed between the internal thread and the thread runout by an installation motion of the core bolt simultaneously with a generation of a compressive load on the sleeve. The insert deforms simultaneously with and facilitates a formation of a bulb in the sleeve in response to the compression.