Caution: Consult all relevant material safety data sheets. Chemicals used for the tests are toxic and carcinogenic. Use personal protective equipment (safety glasses, gloves, lab coat, full-length pants, and closed-toe shoes).
1. Setup for Tests
<ol>
	<li>Preparation of samples
	<ol>
		<li>Cut strips of fabric along the direction perpendicular to the fibers (in order to test wicking in the fiber direction). 
		NOTE: The lengths of the strips are calculated in order to obtain a defined fiber volume ratio. For carbon fabrics, to obtain Vf = 40%, the length of the strips was 150 mm. For untreated and treated flax, to achieve the same Vf, the length was 365 mm. The width of each strip will be equal to the height of sample holder, which is 20 mm (Figure 1).</li>
		<li>Roll the strips tightly to allow their insertion into the cylindrical sample holder of R = 6 mm.</li>
		<li>Add a thin paper filter between the sample holder and the sample reinforcements (in order to suppress the effect of the sample holder on the wicking). The maximum thickness of the paper filter should be 0.1 mm.</li>
		<li>Insert the sample into the cylinder and screw the drilled cap at the bottom and the piston at the top in order to ensure compaction.</li>
		<li>Clamp the sample holder with the fabric to the tensiometer.</li>
	</ol>
	</li>
	<li>Preparation of liquids
	<ol>
		<li>Fill a vessel with the liquid test and place it into the specific receptacle of the tensiometer. Use vessels made of borosilicate glass and with a diameter of 70 mm.</li>
		<li>For the first test (step 2.1), use n-hexane. For the second test (step 2.3), use water. Ensure that the liquid in the vessel reaches a height of at least 12 mm.</li>
	</ol>
	</li>
	<li>Experimental parameters
	<ol>
		<li>Set the surface detection threshold to 8 mg and the translation speed of the liquid vessel at 0.5 mm/s for detection of the liquid.</li>
	</ol>
	</li>
</ol>
2. Wicking tests
NOTE: After the preparation of samples and the setup of the tensiometer parameters, the wicking tests can start. The liquid vessel moves up until the liquid is in contact with the sample holder. Then, liquid rises into the sample holder, and the tensiometer measures the squared liquid mass gain over time. Data are recorded by the software provided with the tensiometer. One curve of mass against time is then visualized for each wicking test.
<ol>
	<li>Initial test for determining the geometric factor:
	<ol>
		<li>Use a totally-wetting liquid (for which the contact angle is 0&#176;), such as n-hexane.</li>
		<li>Stop the wicking test when the visualized curve achieves a constant value. This indicates that the liquid has reached the top of the sample holder and thus that the wicking is complete.</li>
		<li>Fit the linear trend of the wicking curve (m2(t)) with the Washburn equation: 
		<img alt="Equation 3" src="/files/ftp_upload/55059/image003.jpg" />&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(3) 
		Since the advancing contact angle is supposed 0&#176; with n-hexane, from the slope of linear fit, determine the geometric constant, C (mm5). 
		NOTE: All tests were carried out under standard conditions at 20 &#176;C. A change in temperature will modify the liquid surface tension and the results.</li>
	</ol>
	</li>
	<li>Cleaning of sample holder for the following tests 
	NOTE: After removing the wet fabric, the sample holder has to be cleaned perfectly to prevent errors in the following measurements.
	<ol>
		<li>Immerse the sample holder in a vessel with sulfochromic acid (50% of a saturated solution of potassium dichromate and 50% of concentrated sulfuric acid) for 30 sec.</li>
		<li>Rinse it with distilled water and then dry it.</li>
	</ol>
	</li>
	<li>Second test for determining the apparent advancing contact angle
	<ol>
		<li>Use the liquid for which the advancing contact angle has to be measured with a new, identical, and dry fabric sample. 
		NOTE: Water was used in order to validate the method.</li>
		<li>Stop the wicking test when the visualized curve achieves a constant value. This indicates that the liquid has reached the top of the sample holder and that the capillary rise is complete.</li>
		<li>Fit the linear part of the wicking curve (m2(t)) with the Washburn equation (Equation 3), since the constant, C, is already known due to the first test (step 2.1), with the slope of linear fit determining the advancing contact angle, &#952;a (&#176;). 
		NOTE: All tests were carried out under standard conditions at 20 &#176;C. A change in temperature will modify the liquid surface tension and the results.</li>
	</ol>
	</li>
	<li>Evaluation of the liquid weight contribution due to the sample holder 
	NOTE: The tensiometer, as a microbalance, measures the total mass of liquid, including both the liquid ascending in the fabric and the contribution of the external meniscus on the sample holder and the wicking in the filter. Those contributions must be isolated.
	<ol>
		<li>Put the same amount of filter paper as used in step 1.1.3 into the sample holder and repeat steps 2.1.1-2.1.2.</li>
		<li>Subtract the constant value obtained (m2) from the data recorded in step 2.1.3 and shift the curve to assess the correct evaluation of the geometric constant, C.</li>
		<li>Fill the sample holder with only the filter paper and repeat steps 2.3.1-2.3.2.</li>
		<li>Subtract the constant value obtained (m2) from the data recorded in step 2.3.3 and shift the curve to assess the correct evaluation of the advancing contact angle, &#952;a.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Lawrence, J. M., Neacsu, V., Advani, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+the+impact+of+capillary+pressure+and+air+entrapment+on+fiber+tow+saturation+during+resin+infusion+in+lcm.">Modeling the impact of capillary pressure and air entrapment on fiber tow saturation during resin infusion in lcm.</a> Compos Part A: Appl Sci Manuf. 40 (8), 1053-1064 (2009).</li><li>Ravey, C., Ruiz, E., Trochu, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+optimal+impregnation+velocity+in+resin+transfer+molding+by+capillary+rise+experiments+and+infrared+thermography.">Determination of the optimal impregnation velocity in resin transfer molding by capillary rise experiments and infrared thermography.</a> Compos Sci Technol. 99, 96-102 (2014).</li><li>Verrey, J., Michaud, V., M&#229;nson, J. -. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+capillary+effects+in+liquid+composite+moulding+with+non-crimp+fabrics.">Dynamic capillary effects in liquid composite moulding with non-crimp fabrics.</a> Compos Part A: Appl Sci Manuf. 37 (1), 92-102 (2006).</li><li>Abouorm, L., Moulin, N., Bruchon, J., Drapier, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monolithic+approach+of+Stokes-+Darcy+coupling+for+LCM+process+modelling.">Monolithic approach of Stokes- Darcy coupling for LCM process modelling.</a> Key Eng Mater. 554, 447-455 (2013).</li><li>Washburn, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Note+on+a+method+of+determining+the+distribution+of+pore+sizes+in+a+porous+material.">Note on a method of determining the distribution of pore sizes in a porous material.</a> Proc Natl Acad Sci USA. , 115-116 (1921).</li><li>Pucci, M. F., Liotier, P. -. J., Drapier, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+effects+on+flax+fibers-modification+and+characterization+of+the+wetting+dynamics.">Capillary effects on flax fibers-modification and characterization of the wetting dynamics.</a> Compos Part A: Appl Sci Manuf. 77, 257-265 (2015).</li><li>Darcy, H., Dalmont, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Les fontaines publiques de la ville de Dijon: exposition et application. , (1856).</li><li>Pucci, M. F., Liotier, P. -. J., Drapier, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+wicking+in+a+fibrous+reinforcement-orthotropic+issues+to+determine+the+capillary+pressure+components.">Capillary wicking in a fibrous reinforcement-orthotropic issues to determine the capillary pressure components.</a> Compos Part A: Appl Sci Manuf. 77, 133-141 (2015).</li><li>Pucci, M. F., Liotier, P. -. J., Drapier, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+wicking+in+flax+fabrics+-+effects+of+swelling+in+water.">Capillary wicking in flax fabrics - effects of swelling in water.</a> Colloids Surf A: Physicochem Eng Aspects. 498, 176-184 (2016).</li><li>Nguyen, V. H., Lagard&#232;re, M., Park, C. H., Panier, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Permeability+of+natural+fiber+reinforcement+for+liquid+composite+molding+processes.">Permeability of natural fiber reinforcement for liquid composite molding processes.</a> J Mater Sci. 49 (18), 6449-6458 (2014).</li><li>Stuart, T., McCall, R., Sharma, H., Lyons, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modelling+of+wicking+and+moisture+interactions+of+flax+and+viscose+fibres.">Modelling of wicking and moisture interactions of flax and viscose fibres.</a> Carbohydr Polym. 123, 359-368 (2015).</li></ol>

The authors have nothing to disclose.

The critical steps in the protocol relate to the preparation of the samples. Firstly, the rolled sampled have to be tight in order to make the assumption of a homogeneous fiber volume ratio. If there is a tightness gradient in the sample, the Washburn equation5,6 cannot be used to fit the wicking curves. In addition, the boundary conditions between the fabric and the sample holder are difficult to control. Thus, the filter paper (1.1.3) must also be carefully inserted into the sample holders8.
Some modifications of the technique can be made to analyze other directions of wicking in order to evaluate orthotropic effects in capillary pressure8. For instance, one can cut strips along the direction of fibers, in order to test the wicking in the direction perpendicular to the fibers (in the reinforcement plane); or one can cut discs of reinforcements of the cylindrical sample holder radius and stack them in order to test wicking in the transverse direction.
However, the procedure is limited by the Washburn hypothesis5. In addition, the method is limited in terms of sample size, as neither longer nor larger samples can be processed currently. This must be addressed for certain types of weaving, such as larger tows.
This method is currently the only one that allows the determination of capillary pressure during spontaneous impregnation. This parameter is of primary importance for the simulation of composite manufacturing and void formation in industrial composite parts manufactured by liquid composite molding processes.
Critical steps may have to be improved for further applications. Modifications of the sample holder will be made in order to move all of the actual boundaries. Another future application is to use the procedure to determine the capillary pressure with resin, which is the final purpose of the LCM processes.

During impregnation of fibrous reinforcements in liquid composite molding (LSM) processes, the resin flow is driven by a pressure gradient. Capillary effects have an additional effect that can compete with the pressure gradient, depending on the process parameters. Their influence on the process thus has to be evaluated1,2. This can be done by defining an apparent capillary pressure, Pcap, modifying the initial pressure gradient3. This parameter may subsequently be inserted into numerical models in order to simulate flows during processes and to accurately predict void formation4.
The spontaneous impregnation of a fabric by a liquid (wicking) can be described by the Washburn equation5. Originally, the Washburn equation described the capillary rise of a liquid in a tube. This equation was then extended for porous structures, such as fibrous reinforcements, that can be approximated to a capillary tube network. Considering a cylindrical sample holder with a radius, R, filled with a porous medium, the Washburn equation was modified in the form of squared mass gain (m&#178;(t)) over time, as follows6:
<img alt="Equation 1" src="/files/ftp_upload/55059/image001.jpg" />&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(1)
where c is a parameter that accounts for tortuosity, &#7773; is the mean pore radius, and &#949; = 1-Vf is the porosity (Vf being the fiber volume ratio). All parameters in the square brackets concern the morphology and configuration of the porous medium, and they can be consolidated into a constant, C, referred to as the &#34;geometric porous medium factor.&#34; The other parameters express the dependence of wicking on the interactions between the medium and the liquid (through &#961;, &#951;, and &#947;L, which are, respectively, the density, viscosity, and surface tension of the liquid, and through &#952;a, an apparent advancing contact angle).
In parallel, the flow through a porous medium is usually modelled with the well-known Darcy law7, which relates an equivalent fluid velocity, vD, to the pressure drop through the permeability of the medium, K, and the liquid viscosity, &#951;. This equation also allows for the expression of the mass gain over a square root of time and thus for the consideration of the equivalence between the two equations. From this equivalence between the Washburn equation and the Darcy law, the capillary pressure was then defined as follows8:
<img alt="Equation 2" src="/files/ftp_upload/55059/image002.jpg" />&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;(2)
Here, the main focus is to describe the experimental procedure to measure the geometric factors and the apparent advancing contact angles for unidirectional fabrics, with the aim of determining the capillary pressure. This method relies on using a tensiometer to perform wicking tests (Figure 1). A tensiometer is a microbalance with a resolution of 10 &#181;g that measures the liquid mass either forming a meniscus around a solid or ascending a fibrous medium. Wicking tests were carried out considering a one-dimensional characterization (direction along the fibers)8,9. Quasi-unidirectional fabrics used to validate the procedure were carbon uni-directional (UD) fabrics at a Vf = 40%. Once the method was validated, flax fabrics were submitted to a thermal treatment that modifies the wetting behavior of fibers6, and wicking tests were performed with different fiber volume ratios (from 30% to 40%) for both untreated and treated flax fabrics. To determine morphological and wetting parameters, at least two wicking tests are mandatory: the first one with a totally-wetting liquid, like n-hexane, to determine C (Equation 1), and the second one with the liquid of interest, to determine the apparent advancing contact angle once C is known. In the first approach, water was used to evaluate the procedure.
This method can be applied to different fabrics and liquids, allowing for the evaluation of the influence of material geometry (morphology of fabrics), porosity (different fiber volume ratios), and viscosity and surface tension of liquid on the capillary impregnation phenomena. It is obvious that the procedure according to the Washburn theory (Equation 1) can be adopted only if wicking curves (m&#178;(t)) recorded by the tensiometer have a linear trend. This means that the parameters in Equation 1 must remain constant during the entire wicking process. If this is not the case, as for flax reinforcements in water, because fibers undergo swelling10,11, the Washburn equation should be modified to include the effect of swelling in order to describe the tests properly9. Treated fabrics were found to be less sensitive to water sorption9. Geometric factors and wetting parameters can be measured from linear fits, allowing for the calculation of the capillary pressure, Pcap.

<table><tbody><tr><td>Carbon UD fabrics</td><td>Hexcel&amp;nbsp;</td><td>48580</td><td></td></tr><tr><td>Flax UD fabrics</td><td>Libeco</td><td>FLAXDRY UD 180</td><td></td></tr><tr><td>n-Hexane</td><td>Sigma Aldrich</td><td></td><td></td></tr><tr><td>Sulfochromic acid</td><td>home made</td><td></td><td>toxic and corrosive</td></tr><tr><td>Filter paper</td><td>Dataphysic</td><td>FP11</td><td></td></tr><tr><td>Tensiometer</td><td>Dataphysic</td><td>DCAT11</td><td></td></tr></tbody></table>

wicking tests for unidirectional fabrics: measurements of capillary parameters to evaluate capillary pressure in liquid composite molding processes

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure.

Curves of mass gain during wicking obtained with the tensiometer for carbon and untreated and treated flax fabrics are shown in Figures 2 and 3. All curves are shown after the subtraction of both weights of the external meniscus due to the sample holder and filter paper and are shifted to zero.
It is possible to observe from the plots in Figure 2 that, with both n-hexane and water, a linear fit of Equation 1 with experimental wicking is well-achieved if the fabrics are inserted properly in the sample holder. The use of a filter paper is mandatory to ensure the repeatability of measurements. This makes it possible to set the constant, C, and then to calculate an apparent advancing contact angle, &#952;a. Curves reach an asymptotic equilibrium that is given by the height of the sample itself, which is limited to 20 mm to ensure the capillary-driven flow. The equilibrium weight is due to the saturation of the porous medium by the test liquid. It is thus related to the fiber volume ratio and the sample holder inner volume (i.e., porosity, &#949;). With the derived constant, C, and the apparent advancing contact angle, &#952;a (Table 1), it is possible to determine the capillary pressure, Pcap, along the fiber direction for unidirectional carbon fabrics.
Like the carbon fabrics, wicking tests for untreated and treated flax reinforcements were carried out. Figure 3 (left) shows experimental curves obtained on five tests for n-hexane. A linear trend was observed for both treated and untreated flax fabrics, allowing for the determination of the geometric factors. Only a slight difference was observed between untreated and treated fabrics, indicating an eventual decrease of tortuosity with treatment, but not demonstrating a significant modification of morphology. A significant effect of treatment on flax reinforcement is shown on Figure 3 (right). It is obvious that a linear fit is possible on treated fabrics, while untreated ones clearly show a non-linear trend. Average results over five tests for the three types of reinforcements are presented in Table 1. It will thus be possible, after measurements of fabrics permeabilities, to calculate with Equation 2 an equivalent capillary pressure for only treated fabrics. Differences in wicking are due to the sensitivity to water that induce the swelling of flax fibers. Swelling of natural fibers during wicking causes an increase in the fiber volume ratio, which causes the equilibrium weight to be reached more slowly. It also induces a smaller equilibrium weight due to the diminution in porosity. The capillary rise was already found to be faster for chopped, treated flax yarns; this result is thus coherent6. Treatment makes fibers less sensitive to water sorption9, and this can thus explain the differences in wicking for untreated and treated fabrics. A modified Washburn equation that includes the effect of swelling is then used to fit the experimental data of wicking in flax fabrics, allowing for the determination of the capillary pressure, Pcap9.
<img alt="Figure 1" src="/files/ftp_upload/55059/55059fig1.jpg" /> 
Figure 1: Scheme of the tensiometer (left) and the cylindrical sample holder (right)8. This scheme represents the tensiometer setup (left) and depicts the moving vessel and the weighing apparatus, which records the sample weight over time. The sample holder is shown on the right part of the scheme. The piston and the drilled cap ensuring the compaction of the fabrics can be seen. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55059/55059fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55059/55059fig2.jpg" /> 
Figure 2: Washburn fit of two experimental tests in the x-direction, with n-Hexane (left) and water (right). The tests refer to carbon fabrics with Vf= 40%8. The aim of this figure is to show that the first part of the capillary wicking graph is linear, plotting the squared mass gain against time. It also shows that this is verified for each test liquid. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55059/55059fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55059/55059fig3.jpg" /> 
Figure 3: Wicking curves obtained with n-Hexane (left) and water (right) for untreated and treated flax fabrics at Vf= 40%9. These graphs clearly show that there is a large difference between untreated and treated flax fabrics. While a linear fit can be achieved with n-Hexane for both fabrics, it is impossible for untreated flax with water. This is due to the swelling of the flax fibers. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55059/55059fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Type of fabrics</td>
			<td>c&#7773; (&#181;m)</td>
			<td>&#952;a (&#176;)</td>
		</tr>
		<tr>
			<td>Carbon UD&#160;</td>
			<td>12.1 &#177; 1.5</td>
			<td>74.8 &#177; 2.3</td>
		</tr>
		<tr>
			<td>Untreated flax UD&#160;</td>
			<td>12.2 &#177; 1.4</td>
			<td>?</td>
		</tr>
		<tr>
			<td>Treated flax UD&#160;</td>
			<td>15.3 &#177; 1.3</td>
			<td>72.1 &#177; 1.8</td>
		</tr>
	</tbody>
</table>
Table 1: Average measured values of the geometric product and the apparent advancing contact angle on carbon and on untreated and treated flax fabrics. This table presents the average values over five tests for each fabric, derived from the linear fit of experimental graphs (m2(t)) with the Washburn equation.

Watch this Scientific Journal Video about Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes at JoVE.co

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

An experimental method to measure geometrical parameters and the apparent advancing contact angles describing capillary wicking in unidirectional synthetic and natural fabrics is proposed. These parameters are mandatory for the determination of the capillary pressures that must be taken into account for liquid composite molding (LCM) applications.

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify ...

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8.7K Views.  Mines Saint-Étienne.  Een experimentele methode om geometrische parameters en de schijnbare voortschrijdende contacthoeken beschrijven capillaire wicking in één richting synthetische en natuurlijke stoffen wordt voorgesteld te meten. Deze parameters zijn verplicht voor de bepaling van de capillaire druk die wordt gehouden voor vloeibare composietbedrijven (LCM) toepassingen worden genomen. 

Video: Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

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The durability of polymers and fiber-reinforced polymer composites in service is a critical aspect for their designs and condition-based maintenance. We present a novel low-cost laboratory testing platform for the investigation of the influence of concurrent mechanical and environmental loadings, and may help design more efficient yet safer composite structures.

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A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

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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.

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Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose and short sisal fibers are dispersed into a water suspension containing bacterial cellulose. The fiber and nanocellulose suspension is then filtered (using vacuum or gravity) and the wet filter cake pressed to squeeze out any excess water, followed by a drying step. This will result in the hornification of the bacterial cellulose network, holding the loose natural fibers together.
Our method is specially suited for the manufacturing of rigid and robust preforms of hydrophilic fibers. The porous and hydrophilic nature of such fibers results in significant water uptake, drawing in the bacterial cellulose dispersed in the suspension. The bacterial cellulose will then be filtered against the surface of these fibers, forming a bacterial cellulose coating. When the loose fiber-bacterial cellulose suspension is filtered and dried, the adjacent bacterial cellulose forms a network and hornified to hold the otherwise loose fibers together.
The introduction of bacterial cellulose into the preform resulted in a significant increase of the mechanical properties of the fiber preforms. This can be attributed to the high stiffness and strength of the bacterial cellulose network. With this preform, renewable high performance hierarchical composites can also be manufactured by using conventional composite production methods, such as resin film infusion (RFI) or resin transfer molding (RTM). Here, we also describe the manufacturing of renewable hierarchical composites using double bag vacuum assisted resin infusion.

We present a novel method of manufacturing rigid and robust short natural fiber preforms using a papermaking process. Bacterial cellulose acts simultaneously as the binder for the loose fibers and provides rigidity to the fiber preforms. These preforms can be infused with a resin to produce truly green hierarchical composites.

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose ...

Bioengineering

Deposition of Porous Sorbents on Fabric Supports

A microwave deposition technique for silanes, previously described for production of oleophobic fabrics, is adapted to provide a fabric support material that can be subsequently treated by dip coating. Dip coating with a sol preparation provides a supported porous layer on the fabric. In this case, the porous layer is a porphyrin functionalized sorbent system based on a powdered material that has been demonstrated previously for the capture and conversion of phosgene. A representative coating is applied to cotton fabric at a loading level of 10 mg/g. This coating has minimal impact on water vapor transport through the fabric (93% of the support fabric rate) while significantly reducing transport of 2-chloroethyl ethyl sulfide (CEES) through the material (7% of support fabric rate). The described approaches are suitable for use with other fabrics providing amine and hydroxyl groups for modification and can be used in combination with other sol preparations to produce varying functionality.

This report details a microwave-initiated approach for deposition of porphyrin functionalized porous organosilicate sorbents on a cotton fabric and demonstrates reduction in 2-chloroethyl ethyl sulfide (CEES) transport through the fabric resulting from this treatment.

A microwave deposition technique for silanes, previously described for production of oleophobic fabrics, is adapted to provide a fabric support material ...

Chemistry

Magnet Assisted Composite Manufacturing: A Flexible New Technique for Achieving High Consolidation Pressure in Vacuum Bag/Lay-Up Processes

This work demonstrates a protocol to improve the quality of composite laminates fabricated by wet lay-up vacuum bag processes using the recently developed magnet assisted composite manufacturing (MACM) technique. In this technique, permanent magnets are utilized to apply a sufficiently high consolidation pressure during the curing stage. To enhance the intensity of the magnetic field, and thus, to increase the magnetic compaction pressure, the magnets are placed on a magnetic top plate. First, the entire procedure of preparing the composite lay-up on a magnetic bottom steel plate using the conventional wet lay-up vacuum bag process is described. Second, placement of a set of Neodymium-Iron-Boron permanent magnets, arranged in alternating polarity, on the vacuum bag is illustrated. Next, the experimental procedures to measure the magnetic compaction pressure and volume fractions of the composite constituents are presented. Finally, methods used to characterize microstructure and mechanical properties of composite laminates are discussed in detail. The results prove the effectiveness of the MACM method in improving the quality of wet lay-up vacuum bag laminates. This method does not require large capital investment for tooling or equipment and can also be used to consolidate geometrically complex composite parts by placing the magnets on a matching top mold positioned on the vacuum bag.

A new technique for applying consolidation pressure on the vacuum bag lay-up to fabricate composite laminates is described. The goal of this protocol is to develop a simple, cost-effective technique to improve the quality of laminates fabricated by the wet lay-up vacuum bag method.

This work demonstrates a protocol to improve the quality of composite laminates fabricated by wet lay-up vacuum bag processes using the recently developed ...

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

Cutting Procedures, Tensile Testing, and Ageing of Flexible Unidirectional Composite Laminates

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, where the yarns in each layer are oriented parallel to each other and held in place using binder resins and thin polymer films. The armor is constructed by stacking the unidirectional layers in different orientations. To date, only very preliminary work has been performed to characterize the ageing of the binder resins used in unidirectional laminates and the effects on their performance. For example, during the development of the conditioning protocol used in the National Institute of Justice Standard-0101.06, UD laminates showed visual signs of delamination and reductions in V50, which is the velocity at which half of the projectiles are expected to perforate the armor, after ageing. A better understanding of the material property changes in UD laminates is necessary to comprehend the long-term performance of armors constructed from these materials. There are no current standards recommended for mechanically interrogating unidirectional (UD) laminate materials. This study explores methods and best practices for accurately testing the mechanical properties of these materials and proposes a new test methodology for these materials. Best practices for ageing these materials are also described.

The goal of the study was to develop protocols to prepare consistent specimens for accurate mechanical testing of high-strength aramid or ultra-high-molar-mass polyethylene-based flexible unidirectional composite laminate materials and to describe protocols for performing artificial ageing on these materials.

Many body armor designs incorporate unidirectional (UD) laminates. UD laminates are constructed of thin (&#60;0.05 mm) layers of high-performance yarns, ...

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

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