Fiber-modified interlayer for a composite structure

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Solution Overview

Problem

Composite structures reinforced with thermoplastic particles or interlayers face issues with impact resistance and electrical conductivity, particularly susceptibility to edge glow during lightning strikes and reduced mechanical property retention at elevated temperatures.

Innovation Solution

A unidirectional fabric with alternating layers of a reinforcing layer and fiber-modified interlayers, where the interlayers consist of nonwoven fabric layers with discontinuous carbonaceous fibers, providing enhanced impact resistance and electrical conductivity by stabilizing the reinforcing layer and maintaining fiber orientation through knit stitching or melt-bonding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If thermoplastic particles or interlayers are added to enhance impact resistance, then impact resistance is improved, but electrical conductivity deteriorates and edge glow susceptibility increases

Engineering Contradiction:

Improveimpact resistanceVSAvoidelectrical conductivity

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent applies local quality by using thermoplastic interlayers only at specific locations where impact resistance is needed (between fiber layers), while maintaining electrical conductivity in the matrix material and fiber layers. The interlayer is strategically positioned to provide toughness without compromising the overall electrical pathway of the composite structure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs composite materials by combining thermoplastic interlayers with thermosetting matrix materials and conductive fiber layers (carbon, glass, or polyamide). This multi-material approach allows the structure to simultaneously achieve impact resistance from the thermoplastic interlayer and electrical conductivity from the conductive fiber network and thermosetting matrix.

Inventive Principle:

Principle #40Composite materials

2Strength

If thermoplastic interlayers are used to increase impact resistance, then impact resistance is improved, but mechanical property retention at elevated temperatures deteriorates

Engineering Contradiction:

Improveimpact resistanceVSAvoidmechanical property retention at elevated temperatures

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The patent utilizes parameter changes by selecting thermoplastic materials with specific glass transition temperatures and melting points that allow them to remain dimensionally stable at service temperatures while still providing impact toughness. The thermosetting matrix material is chosen to maintain its mechanical properties at elevated temperatures, compensating for any thermal softening of the thermoplastic interlayer.

Inventive Principle:

Principle #35Parameter changes

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 significantly improves the impact resistance and electrical conductivity of composite structures, reducing edge glow and maintaining mechanical properties at elevated temperatures, while also stabilizing the reinforcing layer and maintaining fiber orientation.

Implementation Method 1

each fiber layer comprises carbonaceous fibers... The fiber-modified interlayer significantly improves the impact resistance... of composite structures

Methodology Applied

Scientific EffectImpact energy absorption: Fracture Mechanics

Implementation Method 2

each fiber layer comprises carbonaceous fibers... significantly improves... electrical conductivity... reducing edge glow

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentEP3333293B1Fiber-modified interlayer for a composite structure

Publication Date: 2021.10.13 THE BOEING CO

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AI summary

A fiber-modified interlayer includes a nonwoven fabric layer formed of continuous fibers, and discontinuous fibers attached to the nonwoven fabric, the fiber-modified interlayer is attached to at least one reinforcing layer of structural tows to form an interlayer-toughened reinforcing fabric, at least one layer of the interlayer-toughened reinforcing fabric is infused with a matrix material and cured to form a composite structure.