Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets
November 7th, 2016
The integration of conductive nanoparticles, such as graphene nanoplatelets, into glass fiber composite materials creates an intrinsic electrical network susceptible to strain. Here, different methods to obtain strain sensors based on the addition of graphene nanoplatelets into the epoxy matrix or as a coating on glass fabrics are proposed.
The overall goal of this procedure is to achieve self-sensing properties in composite materials for structural health monitoring. This method can help answer key questions in the sea automatic detection fail, such as quantification of a strain and damage in place of off-shore wind farms and prediction of their server life. The main advantage of this technique is that damage can be detected by the structural component itself.
Though this method can provide insight into structural damage of composite materials, it can also be applied to other systems such as biomechanical analysis during injury recovery. To begin the preparation, in a ductless fume hood, hand-mix 24 grams of functionalized graphene nanoplatelets with DGEBA monomer. To disperse the f-GNPs into the monomer, first sonicate the mixture with a Probe Sonicator for 45 minutes.
Then, calender the mixture three times, increasing the roller speed each time. After dispersion, weigh the mixture. Heat the mixture to 80 degrees Celsius while stirring, and then place the mixture under vacuum.
Degas the mixture while stirring for 15 minutes. Weigh out the hardener in a 100 to 23 weight ratio of DGEBA monomer to hardener. Remove the mixture from vacuum, and stop magnetic stirring.
Add the hardener, and stir by hand until homogeneous. After degassing and hand-mixing, keep the f-GNP epoxy material at 80 degrees Celsius under magnetic stirring. Then, clean a steel plate with acetone.
Using fabric scissors, cut 14 layers of glass fiber fabric to the desired dimensions. Warm the glass fabric to 80 degrees Celsius in an oven. Cut two squares of antiadherent polymer film in the same dimensions as the fabric.
Place the film on the clean steel plate. Using a brush, apply a layer of f-GNP-filled epoxy to one square of the polymer film. Carefully place one square of warmed glass fiber plastic on the epoxy-covered film, so the epoxy and film are completely covered.
Use a de-airing roller to compress the materials. Continue applying layers of epoxy and fabric, compressing each time, until all remaining fabric has been used. Apply one last layer of epoxy, and place the remaining square of antiadherent polymer film on top of the laminate.
Cure the laminate in a hot plate press with increasing pressure. In a ductless fume hood, prepare a one to one mixture of sizing agent to distilled water. Add to this 7.5 grams of f-GNPs.
Remove the mixture from the fume hood, and disperse the nanoplatelets by probe sonication. Cut out 14 squares of glass fiber fabric. Use a Dip Coater to coat the glass fabric with the f-GNP-filled sizing.
Then, dry the coated fabric in a vacuum oven. Clean a steel plate with acetone. Place a square of antiadherent polymer film of the same dimensions as the glass fiber fabric squares on the steel plate.
Place the 14 squares of coated glass fiber fabric onto the polymer film, ensuring that the edges are aligned. Then, place the plate and fabric in a vacuum bag. Using sealant tape, seal the vacuum bag.
Pre-heat the bag in an oven at 80 degrees Celsius. Degas the DGEBA monomer under vacuum while stirring. Add hardener in a 100 to 23 monomer to hardener weight ratio and stir until homogeneous.
Connect a vacuum pump to the vacuum bag and perform leak checks. Connect a length of polymer tubing to the bag and submerge the open end in the epoxy resin. Turn on the vacuum pump to draw the resin into the bag.
Once the glass fabric pile is completely soaked with epoxy resin, turn off the pump, and seal the bag. Cure the laminate in the bag in an oven at 140 degrees Celsius for 8 hours. Then, remove the cured laminate from the vacuum bag.
To begin preparation for strain testing, machine the laminate samples. Then, clean the sample surfaces with acetone. Using silver acrylic conductive paint, draw two narrow lines 20 millimeters apart on each sample.
Lay fine copper wires flat along the wet silver paint to act as electrodes. Once the paint has dried, fix the wires in place with hot-melt adhesive. Configure a mechanical test machine for a flexural test.
For each sample, measure the width and thickness with calipers, before placing the sample in the machine. Set the test speed and start position appropriately for the size and location of the sample. Connect the electrical contacts to a multimeter and measure the initial electrical resistance between the contacts.
Run the flexural test, monitoring the resistance throughout. To prepare for the strain test, cut f-GNP glass fiber fabric to 10 millimeter wide strips. And to fix copper wires to the fabric with silver conductive paint and hot-melt adhesive.
Next, attach the f-GNP glass fiber fabric bands to the thumb and first three fingers of a nitrile glove using hot-melt adhesive. Measure the initial electrical resistance across the fabric on each finger. Perform a sequence of finger bending while recording the electrical resistance.
Begin by bending the thumb, then index, then middle, then ring fingers. Bend all fingers simultaneously. Then, with increased speed, repeat the sequence from thumb to ring finger, and back.
Incorporation of f-GNPs into glass fiber increases the electrical conductivity of the material, which is effected by induced strain. The normalized electrical resistance increases with increasing flexural strain. Breakage of glass fibers at the point of failure disrupts the electrical network, which is seen as a jump in normalized resistance.
When f-GNP glass fiber fabric is applied to the fingers of a nitrile glove, the bending of each finger, and the duration of the movement can be tracked by changes in resistance. Subjecting the f-GNP epoxy and f-GNP glass fiber composite materials to compressive and tensile strain induced slightly different patterns of change in electrical resistance. Below a certain level of compressive strain, normalized electrical resistance gradually decreases with increasing strain.
Beyond that, the resistance increases. However, the normalized electrical resistance increases with tensile strain throughout. After its development, this technique paved the way for researchers in the field of sensing, monitoring material to explore damage in structural components.
After watching this video, you should have a good understanding of how prepare self-sensing composite material, and how monitoring it in real time.
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Overview
This study explores the integration of conductive nanoparticles, specifically graphene nanoplatelets, into composite materials to develop self-sensing properties for structural health monitoring. The proposed methods aim to enhance the detection of strain and damage in composite materials, with potential applications in offshore wind farms and biomechanical analysis.
Key Study Components
Area of Science
- Materials Science
- Nanotechnology
- Structural Health Monitoring
Background
- Composite materials are widely used in various structural applications.
- Self-sensing capabilities can improve damage detection and maintenance.
- Graphene nanoplatelets offer unique electrical properties when integrated into composites.
- Understanding strain and damage in materials is crucial for longevity and safety.
Purpose of Study
- To develop strain sensors using graphene nanoplatelets in composite materials.
- To enable real-time monitoring of structural integrity.
- To explore applications in both offshore wind farms and biomechanical systems.
Methods Used
- Hand-mixing functionalized graphene nanoplatelets with DGEBA monomer.
- Sonication of the mixture to ensure proper dispersion.
- Application of the mixture into epoxy matrices or as coatings on glass fabrics.
- Testing the self-sensing properties of the resulting composite materials.
Main Results
- Successful integration of graphene nanoplatelets into composite materials.
- Demonstrated ability to detect strain and damage autonomously.
- Potential for application in various structural monitoring scenarios.
- Insights gained into the durability and performance of composite materials.
Conclusions
- The method provides a viable approach for self-sensing composite materials.
- Enhancements in structural health monitoring can lead to improved safety.
- Future applications may extend beyond composites to other fields.
Frequently Asked Questions
Executive Industry Relevance
This work demonstrates how graphene nanoplatelet-reinforced composites enable self-sensing capabilities for real-time strain detection, offering a pathway to reduce reliance on external sensors in structural health monitoring. The approach supports predictive maintenance in hard-to-access environments such as offshore wind farms by embedding sensing functionality directly into load-bearing materials. Its extension to biomechanical monitoring via smart fabrics highlights translational relevance for monitoring human movement in rehabilitation and wearable technology development.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of material-structure relationships under mechanical perturbation, supporting hypothesis testing in mechanobiology.
- Operational Value: Provides a label-free, real-time readout of mechanical strain through electrical resistance changes, reducing need for bulky external transducers.
Screening & Assay Development
- Scientific Value: Generates quantitative, exponential resistance-strain relationships that can serve as calibration curves for strain quantification in dynamic systems.
- Operational Value: Facilitates standardization of strain-sensitive materials through reproducible fabrication protocols involving sonication, calendering, and vacuum-assisted curing.
Translational & Preclinical Research
- Scientific Value: Supports disease-relevant biomechanical modeling by enabling precise tracking of joint movement (e.g., finger bending) via resistance changes in wearable smart fabrics.
- Operational Value: Allows continuous monitoring of movement duration and degree, facilitating longitudinal assessment in injury recovery protocols.
Pipeline & Workflow Integration
The method positions self-sensing composites as an enabling technology across early discovery (mechanistic de-risking), screening (assay-ready strain readouts), and translational research (wearable biomechanical monitoring), with reuse potential in both material and biological systems.
- Discovery Biology: Supports hypothesis testing in mechanotransduction by correlating applied strain with measurable electrical outputs in cell-culture-compatible substrates.
- Screening: Delivers reproducible, quantitative resistance changes under flexural strain, enabling comparison of material formulations for strain sensitivity.
- Analytics: Provides normalized electrical resistance as a ratiometric readout that compensates for baseline variability, enhancing data comparability across samples.
- Translational Research: Connects material strain response to human movement monitoring, supporting continuity from bench to wearable prototypes.
- Enterprise Reuse: Establishes a platform technology adaptable to multiple composite matrices and textile substrates, reducing revalidation burden across projects.
Operational & Enterprise Impact
- Scientific Value: Enhances predictive confidence in material behavior under load by providing direct, real-time strain feedback without signal latency.
- Operational Value: Enables standardization of strain-sensitive material production through defined dispersion, layering, and curing steps.
- Strategic Value: Reduces long-term monitoring costs by eliminating discrete sensor deployment and wiring in inaccessible structures.
- Portfolio Impact: Informs risk-adjusted go/no-go decisions in material selection by quantifying strain tolerance and failure-induced network disruption.
Implementation Considerations
- Requires expertise in nanomaterial dispersion, composite fabrication, and electrical characterization.
- Depends on access to probe sonicators, vacuum ovens, hot presses, and precision mechanical testers.
- Necessitates cross-team alignment between materials scientists, electrical engineers, and biomechanists for data interpretation.
- Involves adaptation considerations when transferring from epoxy matrices to textile coatings for wearable applications.
- Practical limitations include sensitivity to environmental factors (e.g., humidity) that may affect baseline conductivity, requiring calibration in use conditions.
Biopharma FAQs
Chapters in this video
0:05
Title
0:44
Preparation of Functionalized Graphene Nanoplatelet (f-GNP)/Epoxy Composite Material
3:14
Preparation of f-GNP/Glass Fiber Fabric and f-GNP/Glass Fiber Composite Material
5:25
f-GNP/Epoxy and f-GNP/Glass Fiber Composite Material Strain Sensor Testing
6:36
f-GNP/Glass Fiber Fabric Strain Sensor Testing
7:37
Results: Strain Monitoring of f-GNP-containing Composite Materials
8:53
Conclusion
