The authors would like to acknowledge the Ministerio de Econom&#237;a y Competitividad of Spain Government (Project MAT2013-46695-C3-1-R) and Comunidad de Madrid Government (P2013/MIT-2862).

1. Preparation of the Functionalized Graphene Nanoplatelet Filled Epoxy for Multiscale Composite Materials
<ol>
	<li>Disperse functionalized graphene nanoplatelets (f-GNPs) into the epoxy resin.
	<ol>
		<li>Weigh 24.00 g of f-GNPs to achieve a 12 wt% of the final nanocomposite material inside a ductless fume hood.</li>
		<li>Add 143.09 g of the bisphenol A diglycidyl ether (DGEBA) monomer and manually mix it to achieve homogeneity.</li>
		<li>Disperse the f-GNPs into the monomer by a twostep method, wh...

<ol>
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L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-monitoring+structural+materials.">Self-monitoring structural materials.</a> Mater Sci Eng R Reports. 22, 57-78 (1998).</li><li>Kandare, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improving+the+through-thickness+thermal+and+electrical+conductivity+of+carbon+fibre/epoxy+laminates+by+exploiting+synergy+between+graphene+and+silver+nano-inclusions.">Improving the through-thickness thermal and electrical conductivity of carbon fibre/epoxy laminates by exploiting synergy between graphene and silver nano-inclusions.</a> Compos Part A Appl Sci Manuf. 69, 72-82 (2015).</li><li>Amjadi, M., Pichitpajongkit, A., Lee, S., Ryu, S., Park, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+stretchable+and+sensitive+strain+sensor+based+on+silver+nanowire-elastomer+nanocomposite.">Highly stretchable and sensitive strain sensor based on silver nanowire-elastomer nanocomposite.</a> ACS Nano. 8, 5154-5163 (2014).</li><li>Alamusi, H. 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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Graphene-based+polymer+nanocomposites.">Graphene-based polymer nanocomposites.</a> Polymer. 52, 5-25 (2011).</li><li>Zaman, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+facile+approach+to+chemically+modified+graphene+and+its+polymer+nanocomposites.">A facile approach to chemically modified graphene and its polymer nanocomposites.</a> Adv Funct Mater. 22, 2735-2743 (2012).</li><li>Moriche, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Morphological+changes+on+graphene+nanoplatelets+induced+during+dispersion+into+an+epoxy+resin+by+different+methods.">Morphological changes on graphene nanoplatelets induced during dispersion into an epoxy resin by different methods.</a> Compos Part B Eng. 72, 199-205 (2015).</li><li>ASTM International. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ASTM D790-15e2, Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. , D790 (2015).</li><li>Gong, S., Zhu, Z. 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The authors have nothing to disclose.

Self-sensor properties of nanoreinforced composite materials are due to the electrical network created by the f-GNPs through the epoxy matrix and along the glass fibers, which is modified when strain is induced. Dispersion of the f-GNPs is then crucial because the electrical behavior of the sensors strongly depends on the microstructure of the material. Here, we present an optimized procedure to achieve a good dispersion of the GNPs into the epoxy matrix and to avoid wrinkling of the nanoparticles, which causes the detri...

Structural health monitoring (SHM) has become increasingly important because of the need to know the remaining life of structures1-3. Nowadays, difficult to access locations, such as offshore wind plants, lead to higher risks in maintenance operations, as well as greater costs2-4. Self-sensing materials constitute one of the possibilities in the field of SHM due to their ability of self-monitoring strain and damage5.
In the case of wind turbines, blades are generally manufactured in glass fiber/epoxy composite materials, which are electrically insulators. In order to confer self-sensing properties to this composite material, an intrinsic electrical network susceptible to strain and damage needs to be created. During the last few years, the incorporation of conductive nanoparticles such as silver nanowires6,7, carbon nanotubes (CNTs)8-10, and graphene nanoplatelets (GNPs)11-13 has been studied to create this electrical network. These nanoparticles can be incorporated into the system as filler into the polymer matrix or by coating the glass fiber fabric14. These materials can be also applied to other industrial fields, i.e., aerospace, automotive and civil engineering5, and coated fabrics can be used as smart materials in biomechanical applications7,15.
Piezoresistivity of these sensors is achieved by three different contributions. The first contribution is the intrinsic piezoresistivity of the nanoparticles; a strain of the structure changes the electrical conductivity of the nanoparticles. However, the main contributions are changes in tunnel electrical resistance, due to modifications in distances between adjacent nanoparticles, and electrical contact resistance, because of variations in the contact area between overlying ones9. This piezoresistivity is higher when 2D nanoparticles are used as a nanofiller compared to 1D nanoparticles because the electrical network presents a higher susceptibility to geometrical changes and discontinuities, usually one order of magnitude superior16.
Due to the 2D atomic character17 and the high electrical conductivity18,19, graphene nanoplatelets have been selected in this work as the nano-reinforcer of multiscale composite materials in order to obtain self-sensors with enhanced sensitivity. Two different ways to incorporate the GNPs into the composite material are studied in order to elucidate possible differences in sensing mechanisms and sensitivity.

<table border="0" cellpadding="0" cellspacing="0" width="816">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Graphene Nanoplatelets</td>
			<td style="width:113px;">XGScience</td>
			<td style="width:319px;">M25</td>
			<td style="width:167px;">NA</td>
		</tr>
		<tr height="21">
			<td height="42" rowspan="2" style="height:42px;width:217px;">Epoxy resin&#160;</td>
			<td rowspan="2" style="width:113px;">Huntsman</td>
			<td style="width:319px;">Araldite LY556</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">XB3473</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Probe sonication</td>
			<td>Hielscher&#160;</td>
			<td>UP400S&#160;</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Three roll mill</td>
			<td style="width:113px;">Exakt</td>
			<td>Exakt 80E (Exakt GmbH)</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Glass fiber fabric</td>
			<td style="width:113px;">Hexcel</td>
			<td>HexForce &#174; 01031 1000 TF970 E UD 4H&#160;</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Hot plate press</td>
			<td style="width:113px;">Fontijne&#160;</td>
			<td>Fontijne LabEcon300</td>
			<td>NA</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Sizing</td>
			<td style="width:113px;">Nanocyl</td>
			<td>SizicylTM</td>
			<td>NA</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:217px;">Multimeter</td>
			<td style="width:113px;">Alava Ingenieros</td>
			<td>Agilent 34410A&#160;</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Strain Gauges</td>
			<td style="width:113px;">Vishay</td>
			<td>Micro-Measurement (MM&#174;) CEA-06-187UW-120&#160;</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Mechanical tests machine</td>
			<td style="width:113px;">Zwick</td>
			<td>Zwick/Roell 100&#160;kN</td>
			<td>NA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:217px;">Conductive silver paint</td>
			<td style="width:113px;">Monocomp</td>
			<td style="width:319px;">16062 &#8211; PELCO&#174; Conductive Silver Paint</td>
			<td>NA</td>
		</tr>
	</tbody>
</table>

strain sensing based on multiscale composite materials reinforced with graphene nanoplatelets

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are proposed to create the electrical network in this work: (a) the incorporation of the nanoplatelets into the epoxy matrix and (b) the coating of the glass fabric with a sizing filled with the same nanoplatelets. Both types of multiscale composite materials, with an in-plane electrical conductivity of ~10-3 S/m, showed an exponential growth of the electrical resistance as the strain increases due to distancing between adjacent functionalized graphene nanoplatelets and contact loss between overlying ones. The sensitivity of the materials analyzed during this research, using the described procedures, has been shown to be higher than commercially available strain gauges. The proposed procedures for self-sensing of the structural composite material would facilitate the structural health monitoring of components in difficult to access emplacements such as offshore wind power farms. Although the sensitivity of the multiscale composite materials was considerably higher than the sensitivity of metallic foils used as strain gauges, the value reached with NH2 functionalized graphene nanoplatelets coated fabrics was nearly an order of magnitude superior. This result elucidated their potential to be used as smart fabrics to monitor human movements such as bending of fingers or knees. By using the proposed method, the smart fabric could immediately detect the bending and recover instantly. This fact permits precise monitoring of the time of bending as well as the degree of bending.

The protocol to obtain two different materials has been described in the procedure. The difference is in the way the nanoreinforcement is incorporated in the composite material to achieve an electrical network that could be used to strain monitoring. The first method consists of the coating of a glass fiber fabric with f-GNP sizing that can be used as a smart fabric (named f-GNP/glass fiber) or as reinforcement of polymer matrix multiscale composite materials (named f-GNP/glass fiber comp...

Watch this Scientific Journal Video about Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets at JoVE.com

Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets

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 electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are ...

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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8.7K Views.  University Rey Juan Carlos. 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 ...