Cooled Fastener Bushing for Composite Rework

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Solution Overview

Problem

Inconsistent composite structures in aircraft, such as delamination near fastener holes, lead to rework challenges, increasing time and cost due to interference fit fasteners causing new inconsistencies or requiring extensive repair.

Innovation Solution

A method involving a fastener and bushing system where the fastener is cooled to reduce its diameter, allowing a precise interference fit without deforming the composite structure, and positioned with a gap to minimize further inconsistencies, enabling efficient rework and installation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If interference fit fasteners are used in composite structures, then structural strength is improved, but inconsistencies such as delamination and cracks may spread or new inconsistencies may form

Engineering Contradiction:

Improvestructural strengthVSAvoidinconsistencies spread

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The fastener is cooled down before installation to reduce its diameter, allowing it to be inserted into the hole without causing delamination or spreading inconsistencies. The interference fit is then achieved after the fastener returns to ambient temperature, providing structural strength without the harmful effects of forced insertion

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The diameter of the fastener is changed by altering its temperature. Cooling the fastener reduces its diameter for easy insertion, while heating it back to ambient temperature creates the interference fit for structural strength, thus resolving the contradiction between installation ease and structural integrity

Inventive Principle:

Principle #35Parameter changes

2Reliability

If extensive repair and patching are performed on inconsistent composite structures, then structural integrity is restored, but time and cost increase significantly

Engineering Contradiction:

Improvestructural integrityVSAvoidrework time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The fastener is pre-cooled to reduce its diameter before installation, allowing it to be inserted into holes in composite structures with existing inconsistencies without causing further damage or requiring extensive repair. This preliminary preparation enables direct installation and restores structural integrity without time-consuming patching

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The problematic aspect of traditional fastener installation (the interference fit that causes delamination and requires extensive repair) is extracted and separated from the insertion process. The fastener is inserted in a reduced state without causing damage, and the interference fit is achieved separately after insertion, eliminating the need for extensive repair work

Inventive Principle:

Principle #2Taking out (Extraction)

3Strength

If traditional fastener installation methods are used, then structural strength is achieved, but the process requires extensive repair and increases rework time

Engineering Contradiction:

Improvestructural strengthVSAvoidrework efficiency

Core Design Contradiction:

StrengthVSProductivity

Solution Approach 1:

The fastener's diameter is dynamically changed through temperature control: cooled to a reduced diameter for easy insertion into composite structures, then allowed to return to ambient temperature to achieve the interference fit for structural strength. This eliminates the need for extensive repair and significantly improves rework efficiency

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The traditional mechanical force-based insertion method (which causes delamination and requires repair) is replaced with a thermal-based system. Temperature control is used to adjust the fastener's dimensions, allowing damage-free insertion followed by interference fit achievement without extensive repair, thus improving productivity

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 reduces the time and cost associated with reworking composite structures by minimizing the spread of inconsistencies and maintaining structural integrity, allowing for faster and more efficient repair without extensive patching or discarding.

Implementation Method 1

the fastener is cooled to reduce its diameter

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentUS10508669B2Rework system for composite structures

Publication Date: 2019.12.17 THE BOEING CO

AI summary

A method and apparatus for reworking a composite structure. A fastener is cooled from a first temperature to a second temperature at which a diameter of a post of the fastener is reduced by a desired amount. The post of the fastener is placed into a channel in a bushing such that a desired interference fit occurs when the fastener is at the first temperature. The bushing with the fastener is positioned in a hole in the composite structure. A gap is present between an outer surface of the bushing and an inner surface of the hole. A gap is also present between an end of the bushing and a second structure.