Textured Fastener Sleeve for Composite Lightning Protection
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Solution Overview
Problem
Drilling fastener holes in composite materials for aircraft creates machining-induced defects and poor electrical contact, leading to lightning-related issues such as arcing and sparking due to the high resistance of carbon fibers and epoxy, and the anisotropic nature of composite structures.
Innovation Solution
A fastener system with a textured sleeve that expands to fill machining-induced voids, featuring a tubular portion with a textured outer surface and a low-friction inner surface, made from A286 stainless steel, which engages with the composite material to displace sealant and provide intimate contact, reducing the risk of arcing during lightning strikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a smooth sleeve is used in the fastener hole, then the installation process is simpler, but the sleeve cannot eliminate gaps caused by machining-induced texture, resulting in poor electrical contact and increased arcing risk
Solution Approach 1:
The sleeve surface is textured with a specific roughness profile (Ra 0.8-2.0 micrometers) to create localized asperities that engage with the composite material's voids and protrusions. This local quality change enables the sleeve to conform to the irregular hole surface, eliminating gaps and improving electrical contact without complicating the overall installation process
Solution Approach 2:
The sleeve is pre-textured before installation to anticipate and accommodate the machining-induced texture in the composite hole. This preliminary surface preparation ensures that when the sleeve is installed, its textured surface will immediately engage with the hole's irregularities, displacing sealant and creating intimate contact without requiring additional processing steps
2Ease of manufacture
If the sleeve outer surface is made smooth, then manufacturing the sleeve is easier, but the sleeve cannot engage with machining-induced voids, leading to gaps and poor electrical contact
Solution Approach 1:
Instead of making the entire sleeve complex, only the outer surface is textured with controlled roughness (Ra 0.8-2.0 micrometers). This localized modification provides the necessary engagement capability with machining-induced voids while keeping the manufacturing process relatively simple and maintaining uniformity in other critical dimensions
Solution Approach 2:
The sleeve outer surface roughness parameter is specifically controlled within the range of Ra 0.8-2.0 micrometers. This parameter change transforms the surface from smooth to textured, enabling it to engage with the composite material's irregularities and displace sealant, thereby achieving better contact conformity without excessive manufacturing complexity
3Reliability
If carbon fibers have high electrical resistance, then lightning current dissipation is reduced, but this high resistance causes arcing and sparking at the fastener interface during lightning strikes
Solution Approach 1:
The textured sleeve surface creates numerous localized contact points with the carbon fibers in the composite material. These distributed contact points provide multiple parallel paths for lightning current to flow from the fastener into the composite structure, reducing current density at any single point and minimizing the risk of arcing and sparking despite the inherently high resistance of carbon fibers
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 textured sleeve minimizes fastener arcing, enhances electrical contact between carbon fibers and the fastener, fills gaps, and improves mechanical interlocking, effectively mitigating lightning-induced sparking and ensuring safe current transfer.
Implementation Method 1
the texture of the outer surface of the tubular portion of the sleeve engages with voids present within the inner surface of the hole. The deformation of the texture of the outer surface of the tubular portion displaces sealant from the voids of the composite material
Implementation Method 2
The sleeve is adapted to expand radially over the shank portion of the pin member to form an interference fit between the outer surface of said sleeve and the hole of the structure so as to provide an installed position of the fastener
Data Source
AI summary
A fastener adapted to be installed in a hole of a composite structure includes a sleeve, a pin member, and a locking member. The sleeve has an outer surface having an outer diameter. The outer surface of the sleeve is textured. The outer diameter of the tubular portion is less than an inner diameter of the hole of the structure. The pin member has a shank portion. The sleeve is adapted to expand radially over the shank portion of the pin member to form an interference fit between the outer surface of the sleeve and the hole of the structure so as to provide an installed position of the fastener. When the fastener is in the installed position, the texture of the outer surface of the tubular portion deforms to engage with voids of the composite material present on the inner surface of the hole.