Conductive Fiber Prepreg for Lightning Strike Protection
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Solution Overview
Problem
Composite materials used in aerospace structures are vulnerable to lightning strikes due to low electrical conductivity in the z-direction, leading to potential catastrophic damage, and existing solutions to enhance conductivity often increase weight and compromise mechanical properties.
Innovation Solution
A prepreg comprising a structural layer of packed unidirectional conductive fibers with thermosetting resin in the interstices and an outer layer of resin essentially free of conductive fibers, which, when cured, creates a composite laminate with enhanced z-direction conductivity through the dispersion of conductive fibers in the resin interleaf layers, achieved by controlled disruption of fibers during the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conductive elements are added to enhance z-direction conductivity, then lightning strike resistance is improved, but weight of the composite material increases
Solution Approach 1:
The conductive fibres already present in the structural layers serve dual purposes: maintaining structural integrity and providing electrical conductivity. The fibres in adjacent structural layers self-connect through the resin interleaf to create conductive pathways, eliminating the need for separate conductive additives and avoiding additional weight.
Solution Approach 2:
The resin interleaf layer performs multiple functions simultaneously: it provides mechanical separation between fibre layers, maintains laminate uniformity, and enables electrical conductivity by allowing fibre-to-fibre contact. This multi-functionality eliminates the need for separate conductive elements.
2Reliability
If conductive elements are added to enhance z-direction conductivity, then electrical conductivity is improved, but mechanical properties are compromised
Solution Approach 1:
The existing structural fibres in adjacent layers provide both mechanical strength and electrical conductivity. By enabling these fibres to electrically connect through the resin interleaf, the system uses its existing components for dual purposes without introducing elements that would compromise mechanical properties.
Solution Approach 2:
The resin interleaf maintains a uniform composition without discrete conductive particles or heterogeneous additions. This homogeneity ensures consistent mechanical properties throughout the laminate while the dispersed conductive fibres provide sufficient electrical pathways.
3Strength
If well defined layers of fibre separated by resin are used, then mechanical properties are improved, but z-direction conductivity is reduced
Solution Approach 1:
The resin interleaf layer has locally optimized properties: it is sufficiently thick to provide mechanical separation and uniformity, yet sufficiently thin and permissive to allow conductive fibre-to-fibre contact. This local quality differentiation resolves the contradiction between mechanical layering and electrical conductivity.
Solution Approach 2:
The resin interleaf acts as an intermediary that mediates between the conflicting requirements of mechanical separation and electrical connection. It provides a controlled environment where fibres from adjacent layers can make contact while maintaining the overall layered structure and uniformity.
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 solution provides significant improvements in z-direction conductivity while maintaining mechanical performance, achieving low electrical resistance without increasing the weight of the laminate, as demonstrated by the migration of conductive fibers into the interleaf layers during curing.
Implementation Method 1
the migration of conductive fibres into the interleaf layers during curing
Implementation Method 2
It is believed that this is because of a bridging effect, with the fibres dispersed in the interleaf layer providing electrical contacts between the fibre layers.
Implementation Method 3
when cured under elevated temperature, produces a cured composite material
Implementation Method 4
the resulting laminate is cured, typically by exposure to elevated temperatures
Data Source
AI summary
A prepreg comprising a structural layer of packed unidirectional conductive fibres comprising thermosetting resin in the interstices, and a first outer layer of resin comprising thermosetting resin, and being essentially free of unidirectional conductive fibres, which when cured under elevated temperature, produces a cured composite material comprising a cured structural layer of packed unidirectional conductive fibres and a first outer layer of cured resin comprising unidirectional conductive fibres dispersed within.