Composite Fuselage Barrel Fiber Distortion Reduction

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Solution Overview

Problem

The fabrication of large composite barrel sections for aircraft fuselages often results in out-of-plane fiber distortion due to debulking, which can lead to fiber waviness or wrinkling, interfering with final assembly.

Innovation Solution

A grooved mandrel with a higher coefficient of thermal expansion in the hoopwise direction than the composite ply assembly is used, allowing the mandrel to expand radially during curing, thereby stretching the composite plies and minimizing fiber distortion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If composite materials are wrapped around a male mandrel and vacuum is applied for debulking, then the composite structure becomes thinner and more dense, but out-of-plane fiber distortion (waviness or wrinkling) occurs

Engineering Contradiction:

Improvefiber alignmentVSAvoidcomposite density

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The mandrel's coefficient of thermal expansion in the hoopwise direction is engineered to be greater than that of the composite ply assembly. During cure, thermal expansion causes the mandrel to expand radially, stretching the composite plies circumferentially and preventing fiber distortion while allowing debulking to occur

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The differential thermal expansion between the mandrel and composite materials is utilized to solve the contradiction. As temperature increases during curing, the mandrel expands more than the composite, creating circumferential tension that counteracts the compressive forces causing fiber waviness during vacuum debulking

Inventive Principle:

Principle #37Thermal expansion

2Productivity

If automated tape laying is used to increase material lay up rates, then manufacturing cost is controlled, but fiber distortion occurs during the debulking process

Engineering Contradiction:

Improvematerial lay up rateVSAvoidfiber alignment

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The mandrel's thermal expansion parameters are specifically designed to compensate for fiber distortion that would otherwise occur during high-rate automated tape laying and subsequent debulking. The differential expansion ensures fibers remain aligned even during rapid material placement and vacuum application

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If the mandrel expands radially during cure, then the composite plies are stretched and fiber distortion is minimized, but the circumference of outer plies must be carefully controlled

Engineering Contradiction:

Improvefiber alignmentVSAvoidmandrel design

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The mandrel is designed with specific thermal expansion parameters, particularly a higher coefficient of thermal expansion in the hoopwise direction compared to the lengthwise direction. This anisotropic expansion behavior is engineered to stretch composite plies circumferentially during cure, preventing fiber distortion while maintaining outer ply circumference

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The mandrel itself is constructed from composite materials with tailored properties. By using composite materials for the mandrel, the invention achieves the required differential thermal expansion characteristics while maintaining structural integrity and controlling the expansion behavior during the curing process

Inventive Principle:

Principle #40Composite materials

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

This approach effectively reduces or eliminates out-of-plane fiber distortion by ensuring that the circumferentially oriented reinforcing fibers are stretched, maintaining the circumference of the outer plies and preventing waviness or wrinkling during the debulking process.

Implementation Method 1

the mandrel having a coefficient of thermal expansion in the hoopwise direction that is greater than the coefficient of thermal expansion of the composite ply assembly in the hoopwise direction; raising the temperature and pressure within a volume surrounding the composite ply assembly, the temperature increase being sufficient to cause the circumference of the mandrel to expand and stretch one or more plies

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentEP2452807B1Method for minimizing fiber distortion during fabrication of one-piece composite barrel section

Publication Date: 2015.07.08 THE BOEING CO

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AI summary

A method for fabricating a one-piece composite fuselage section (110) that minimizes out-of-plane fiber distortion. This is accomplished by fabricating a mandrel (14) having a coefficient of thermal expansion in the hoopwise direction that is sufficiently greater than that of the laid-up composite ply assembly. As a result of this differential in the coefficients of thermal expansion in the hoopwise direction, the laid-up composite ply assembly is stretched circumferentially as the mandrel expands radially during cure, thereby eliminating or reducing out-of-plane fiber distortion. At the same time, the mandrel and part being fabricated should have substantially the same coefficient of thermal expansion in the lengthwise direction. As the outer surface of the mandrel increases in circumference, the circumferentially oriented reinforcing fibers of the inner plies are stretched, while the circumferentially oriented reinforcing fibers of the outer plies do not reduce in circumference and thus do not form waves or wrinkles.