Direct Fabrication of Piezo-Resistive Strain Sensors on Complex Structures

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Solution Overview

Problem

Conventional strain gauges face challenges in mounting on complex structures like 3D-printed polyetherimide resin or curved surfaces due to the need for tedious surface preparation and limited mechanical flexibility, especially when made of semiconductor or metal alloys.

Innovation Solution

A strain sensing device is fabricated directly on the structure by printing a piezo-resistive material, such as graphene, and creating an electrically conductive strain sensing pattern using laser scanning, eliminating the need for adhesives and surface preparation, and leveraging graphene's mechanical flexibility for higher strain handling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional strain gauge is packaged separately and attached using adhesives, then the strain gauge can be mounted on the structure, but the mounting process requires tedious surface preparation and is prone to reliability issues on complex or curved surfaces

Engineering Contradiction:

Improveadhesion reliabilityVSAvoidmounting complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The strain sensing device is integrated directly into the structure during the additive manufacturing process, merging the structure and sensor into a single unified component. This eliminates the separate mounting step and adhesive application, resolving the contradiction between adhesion reliability and mounting complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The strain sensing device is fabricated in advance as part of the structure during additive manufacturing, before the structure is put into service. This preliminary integration ensures reliable adhesion from the outset and eliminates the need for later mounting operations on complex or curved surfaces.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If conventional strain gauges are made of semiconductor or metal alloys, then they provide strain sensing capability, but they lack inherent mechanical flexibility and are limited to certain strain levels

Engineering Contradiction:

Improvestrain sensing capabilityVSAvoidmechanical flexibility

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The strain sensing device is fabricated from composite materials that combine conductive fillers (such as carbon black, graphite, or metal particles) within a polymer matrix. This composite structure provides both the electrical conductivity needed for strain sensing and the mechanical flexibility required to accommodate various strain levels, resolving the contradiction between measurement precision and adaptability.

Inventive Principle:

Principle #40Composite materials

3Measurement precision

If a packaged strain gauge is used on 3D-printed polyetherimide resin or curved surfaces, then strain measurement can be performed, but the mounting becomes even more difficult and reliability issues increase

Engineering Contradiction:

Improvestrain measurement capabilityVSAvoidmounting difficulty

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The strain sensing device is merged directly into the structure during additive manufacturing, eliminating the need for separate mounting operations on difficult-to-access or curved surfaces. This integration resolves the contradiction between maintaining measurement capability and reducing mounting difficulty.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The mechanical mounting process involving adhesives and surface preparation is replaced by an additive manufacturing process that directly fabricates the strain sensing device as part of the structure. This substitution eliminates the mounting difficulty associated with complex geometries while preserving strain measurement capability.

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 allows for reliable strain measurement on complex structures with improved mechanical flexibility and compatibility with additive manufacturing, achieving higher gauge factors compared to conventional strain gauges.

Implementation Method 1

printing or otherwise depositing a material on the structure, the material exhibiting a piezo-resistive effect

Methodology Applied

Scientific EffectPiezo-resistive effect: Piezoresistive Effect

Implementation Method 2

sintering a strain sensing pattern from the material such that the strain sensing pattern becomes electrically conductive

Methodology Applied

Scientific EffectLaser sintering: Selective Laser Sintering

Data Source

PatentUS11441956B1System and method for fabricating a strain sensing device directly on a structure

Publication Date: 2022.09.13 THE GOVERNMENT OF THE UNITED STATES AS REPRESENTED BY THE SECRETARY OF THE AIR FORCE

AI summary

Various deficiencies in the prior art are addressed by systems, methods, architectures, mechanisms and/or apparatus configured for fabricating a strain sensing device directly on a structure by printing or otherwise depositing a material on the structure, the material exhibiting a piezo-resistive effect, and sintering a strain sensing pattern from the material such that the strain sensing pattern becomes electrically conductive.