Conductive Bushing for CFRP Fastener Electrical Path

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Solution Overview

Problem

Carbon Fiber Reinforced Polymer (CFRP) structures lack electrical conductivity, leading to potential sparking issues due to holes that disrupt continuous electrical paths, particularly in aerospace applications, and require precision machining and exotic materials for thermal expansion matching and corrosion resistance.

Innovation Solution

A compressible expanding bushing with a diameter that increases radially between two diameters to maintain contact points between a fastener and the CFRP structure, using spring pressure to ensure electrical conductivity without the need for precision boring or costly materials, and accommodating thermal expansion through elastic deformation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a precision metal bushing is press fitted into a precision hole in CFRP structure, then electrical conductivity and contact pressure are maintained, but manufacturing complexity and material cost increase significantly

Engineering Contradiction:

Improveelectrical conductivityVSAvoidmanufacturing precision requirement

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The bushing transitions from a rigid precision-fit component to a dynamically adaptable component that can expand and contract. The bushing includes expansion elements that allow it to dynamically adjust its outer diameter to maintain contact pressure with the CFRP structure, eliminating the need for precision machining while ensuring reliable electrical conductivity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The bushing's physical parameters (particularly outer diameter) are made changeable through the expansion mechanism. By changing the bushing's diameter parameter in response to thermal expansion or installation requirements, the system maintains optimal contact pressure without requiring precision-matched dimensions, thereby reducing manufacturing complexity.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If exotic materials with low thermal coefficient of expansion are used to match CFRP, then thermal expansion compatibility is achieved, but material cost and selection limitations increase

Engineering Contradiction:

Improvethermal expansion compatibilityVSAvoidmaterial selection flexibility

Core Design Contradiction:

Stability of the object's compositionVSEase of manufacture

Solution Approach 1:

Instead of relying on material selection to match thermal expansion coefficients, the bushing employs a dynamic expansion mechanism that allows it to adapt to thermal changes. The bushing can expand or contract to maintain contact pressure despite thermal expansion differences, enabling the use of common, corrosion-resistant materials like stainless steel without requiring exotic materials.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention directly addresses thermal expansion by incorporating an expansion mechanism in the bushing that compensates for differential thermal expansion between the metal bushing and CFRP structure. This allows the use of materials with different thermal expansion properties without compromising the electrical connection.

Inventive Principle:

Principle #37Thermal expansion

3Reliability

If high precision machining is performed to maintain contact pressure, then electrical current carrying capacity is ensured, but manufacturing time and cost increase

Engineering Contradiction:

Improvecurrent carrying capacityVSAvoidmanufacturing efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The bushing's dynamic expansion capability ensures that contact pressure is maintained automatically during installation and operation, eliminating the need for high-precision machining. The expansion mechanism compensates for dimensional variations, ensuring reliable electrical contact and current carrying capacity while significantly reducing manufacturing time and cost.

Inventive Principle:

Principle #15Dynamics

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 reliable electrical conductivity while reducing material costs and complexity, maintaining contact pressure over a range of temperatures and preventing sparking, with easy disassembly and reduced risk of CFRP damage.

Implementation Method 1

A bushing having a diameter and a thickness to fit between the first and second diameters extends though and past the thickness of said structure. When the pass through is compressively secured to the structure, the bushing expands radially between the first diameter and the second diameter to maintain at least one contact point between the fastener and the structure.

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS9564728B2Electrically conductive bushing connection to structure for current path

Publication Date: 2017.02.07 THE BOEING CO

AI summary

An electrically conductive structural connection employs a pass through or fastener having a first diameter. A fastener hole, with a second diameter larger than the diameter of the pass through, extends through a thickness of a structure and receives the pass through. A bushing having a diameter and a thickness to fit between the first and second diameters extends though and past the thickness of said structure. When the feedthrough is compressively secured to the structure, the bushing expands radially between the first diameter and the second diameter to maintain at least one contact point between the fastener and the structure.