The authors would like to thank the grants from the National Key Research and Development Program of China (No. 2022YFB3706503) and the Stable Support Plan Program of Shenzhen Natural Science Fund (No. 20220815133826001).

1. Material preparation
<ol>
	<li>Cut eight pieces of 300 mm x 300 mm woven glass fiber fabric with scissors. Tape the cut first to prevent the fiber filaments from falling off. 
	NOTE: Wear a mask and gloves to prevent finger pricking and filament inhalation when cutting the fabric. Not only the woven glass fiber fabric, but unidirectional fabric and other types of fiber, such as carbon fiber and aramid fiber, are also available.</li>
	<li>Weigh out 260 g of epoxy resin and 78 g of hardener according to the mass ratio of 10:3. 
	&#8203;NOTE: The ratio of fiber fabric and resin system is recommended to be 360 g of epoxy resin system per square meter of single layer fiber fabric.</li>
</ol>
2. Fabrication process
NOTE: Figure 1 shows the schematic of fabrication of composite laminate for the hand lay-up process, which is shown in section 2.
<ol>
	<li>WLVB
	<ol>
		<li>Put the fabric in an oven at 60 &#176;C for 8 h.</li>
		<li>Paste isolation film on the acrylic sheet to prevent the resin from bonding.</li>
		<li>Place the mold on the laying area.</li>
		<li>Mix the resin and hardener slowly for 5 min, and then put it into a vacuum chamber to draw out the air bubbles inside.</li>
		<li>Lay the non-porous release film on the mold and fix it with tape around it.</li>
		<li>Lay one peel ply on the non-porous release film.</li>
		<li>Pour in the epoxy resin and use a scraper to distribute the resin evenly throughout the film.</li>
		<li>Ply the first fiber fabric, roll with a naked roller to make sure the resin fully infiltrates the fabric and the bubbles are extruded, and then pour the resin, using a scraper to scrape the resin evenly.</li>
		<li>Repeat steps 2.1.7 and 2.1.8 until all the fabric has been used.</li>
		<li>Lay one peel ply on the fabric and squeeze out the air bubbles manually.</li>
		<li>Lay one perforated release film and one breather fabric successively.</li>
		<li>Place the suction channel and breathable pad on one side.</li>
		<li>Stick a circle of heat-resistant tape with an acrylic sheet outside the mold and attach the vacuum bag around with the tape to form a closed space.</li>
		<li>Turn on the vacuum pump to press 1 bar of pressure for 10 h at room temperature. Then, close the vacuum pump and maintain quiescence for 14 h.</li>
		<li>Put the laminates into the oven at 80 &#176;C for 16 h to cure completely.</li>
		<li>Measure the fiber volume fraction using equations (1-3)38,39. 
		<img alt="Equation 1" src="/files/ftp_upload/65376/65376eq01.jpg" style="margin: auto;" />&#160; &#160; (1) 
		<img alt="Equation 2" src="/files/ftp_upload/65376/65376eq02.jpg" style="margin: auto;" />&#160; &#160; (2) 
		<img alt="Equation 3" src="/files/ftp_upload/65376/65376eq03.jpg" style="margin: auto;" />&#160; &#160; (3) 
		n &#8203;is the number of layers of the laminate,&#160;&#961;fiber is the areal density of the fiber fabric from the manufacturer, Afiber is the area of the laminate, mfiber is the mass of fiber fabric, mtotal is the mass of the laminate, &#961;epoxy&#160;is the density of the epoxy, vepoxy and vtotal&#160;are the volumes of epoxy and laminate, respectively, and is the fiber volume fraction.</li>
	</ol>
	</li>
	<li>WL
	<ol>
		<li>Put the fabric in an oven at 60 &#176;C for 8 h.</li>
		<li>Mix the resin and hardener slowly for 5 min and then put it into a vacuum chamber to draw out the air bubbles inside.</li>
		<li>Lay the non-porous release film on the mold and fix it with tape around it.</li>
		<li>Lay one peel ply on the non-porous release film.</li>
		<li>Pour in the epoxy resin and use a scraper to distribute the resin evenly throughout the film.</li>
		<li>Ply the first fiber fabric, roll with a naked roller to make sure the resin fully infiltrates the fabric and the bubbles are extruded, and then pour the resin, using a scraper to scrape the resin evenly.</li>
		<li>Repeat steps 2.2.5 and 2.2.6 until all the fabric has been used.</li>
		<li>Lay one peel ply on the fabric and squeeze out the air bubbles manually.</li>
		<li>Lay one perforated release film, one breather fabric, and one non-porous release film successively.</li>
		<li>Place one aluminum plate with the same size as the fiber fabric on top.</li>
		<li>Maintain quiescence at room temperature for 14 h.</li>
		<li>Put the laminates into the oven at 80 &#176;C for 16 h to cure completely.</li>
	</ol>
	</li>
</ol>
3. Characterization of impact properties
NOTE: There are many methods for impact testing of composite laminates. Under low-velocity impact conditions, the commonly used method is the drop-weight impact test, while under high-velocity or ultra high-velocity impact conditions, the frequently used method is the bullet impact method. In this study, the drop-weight impact test was applied. The equipment is shown in Figure 2.
<ol>
	<li>Cut a set of 150 mm x 100 mm samples from GFRP for an impact test, according to ASTM D7136, using a high-precision cutting machine.</li>
	<li>Measure the weight and size of each sample.</li>
	<li>Fix the positions of the samples using positioning nails in the centers of the samples that the impactor can contact for every test.</li>
	<li>Fix the sample on the impact support fixture with four rubber tips.</li>
	<li>Conduct the impact test using a drop-weight impact tower at the 10 J energy level. Turn on the drop hammer testing machine and click Connect to connect the controller with the dropdown, then click Home&#160;| Before test. Set the impact energy to 10 J and the additional mass to 2 kg. Input the measurement thickness, 2.1 mm for the WLVB samples and 2.5 mm for the WL samples, to determine the height of the impactor, and click Start to start the experiment.</li>
	<li>Record the impact response data, including force, deflection, and energy history.</li>
	<li>Take out the sample. Record the morphology of the sample after impact.</li>
	<li>Repeat the impact test five times to ensure the repeatability of results.</li>
	<li>Calculate and compare the data of samples.</li>
</ol>
4. Characterization of tensile properties
<ol>
	<li>Cut a set of 250 mm x 25 mm samples from the laminates for a tensile test, according to ASTM D3039, using a high-precision cutting machine with a diamond cutter.</li>
	<li>Measure the size of each sample with a vernier caliper.</li>
	<li>Use epoxy adhesive to bond four 50 mm x 25 mm x 2 mm aluminum tabs on both ends of the sample to avoid stress concentration.</li>
	<li>Spray a thin layer of white paint on the front of the sample, then spray black speckles.</li>
	<li>Place the sample in the center of the clamps of the tensile testing machine and set up the image acquisition system, as shown in Figure 3.</li>
	<li>To ensure the accuracy of the strain data, vary the position of the sample so that it is in the middle of the camera shooting area and in a vertical position. Additionally, adjust the camera focal length and exposure rate to ensure that the spots on the sample are clearly recorded.</li>
	<li>Perform the tensile test. Click CONFIGURE TEST. Set the test&#160;speed to 0.5 mm/min. Click Specimen data. Input the measurement width and thickness of the samples. Click Start, then click Accept current position. Record the load-time data.</li>
	<li>Take out the sample. Record the morphology of the sample after the tensile test.</li>
	<li>Repeat the tensile test five times to ensure the repeatability of results.</li>
	<li>Use digital image correlation (DIC) software to measure the nominal strain of the sample during the tensile test.</li>
	<li>Click Length Scale Image to calibrate the length of the pixels, click Reference Image, and choose the first image as the reference image. Click Deformed Image and choose the remaining images as the deformed images. Click Drawing Tools | Select rectangle to select the measurement area. Click Extensometer and set the length of the extensometer to 100 mm, then click Processing | Start Correlation.</li>
	<li>Divide the load by the cross-sectional area to get the nominal stress.</li>
	<li>Combine the nominal strain from the DIC measurement and the nominal stress from the tensile testing machine.</li>
	<li>Choose the slope of the linear segment of the strain-stress curve as the elastic modulus. Choose the peak value of the tensile force-time curve as the strength.</li>
	<li>Compare the elastic modulus and the strength of samples.</li>
</ol>

Fabrication and Mechanical Property Assessment of Fiber Composite Laminates

The authors do not have any conflicts of interest.

This paper focuses on the two different fabrication processes for the hand lay-up method with low cost. Therefore, two fabrication processes were selected to be carefully described in this paper, which are simpler, easier to master, lower in investment cost, and suitable for production with material modification in laboratories and small-scale factories. During the cure of laminates, high consolidation pressure plays an important role in manufacturing laminates with high quality. The adoption of the traditional WL process without enough external pressure can lead to a high resin volume fraction. High resin volume is one of the major factors that reduce the mechanical properties of laminates. In this work, a fabrication process based on the traditional WL process using a vacuum bag to remove air bubbles and provide pressure is described. In this fabrication process, it is important to control the proportion of materials and sequence of steps. The main factors that affect the mechanical properties of laminates are fiber volume fraction and voids; therefore, protocol steps to remove bubbles, as described in steps 2.1.4, 2.1.8, and 2.1.13, are critical.
To compare the mechanical properties of laminates manufactured by different fabrication processes, the tensile test and low-velocity impact tests are carried out. In this study, laminates manufactured by the WLVB process show better mechanical properties, including tensile strength, tensile modulus, and impact energy absorption. The results illustrate that laminates manufactured using the WLVB process have an increase of 18.3% in specific energy absorption, as well as an increase of 16.3% and 14.6% in tensile strength and modulus, respectively. 
Compared with the WL process, the WLVB process compensates for the insufficient molding pressure through a low-cost vacuum bag, absorbing excess resin from the system to increase the fiber volume fraction and reduce the internal pore content, thereby greatly improving the mechanical properties of the laminate. The quality of laminates manufactured by the WLVB process is better. Due to the pressure exerted by vacuum bag being more uniform, the thickness of the laminate manufactured by the WLVB process is also more uniform. The thickness of the laminate prepared by the WL process using only the weight to provide pressure is uneven, resulting in unstable quality of laminates. The testing results show that the error bars of the tensile and impact properties of the WLVB samples are smaller. It is crucial for the stability of laminate quality to apply uniform pressure during curing.
The WLVB process has important driving significance for the composite material production field with small capital investment. Compared with other preparation processes, the WLVB process has several advantages, including simple equipment requirements and uncomplicated process technology, and the products are not limited by size and shape. This process has a high degree of freedom and can be integrated with metal, wood, plastic, or foam. However, the WLVB process also has some limitations, such as its low efficiency and long cycle. Of note, because it is mainly suitable for small batch production, and laminate performances are closely related to the skill level of operators and construction conditions, it is necessary to design and optimize the manufacturing process quantitatively to achieve a high yield.

Fiber reinforced polymer composite (FRP) is a type of high-strength material manufactured by mixing fiber reinforcement and polymer matrixes1,2,3. It is widely used in the aerospace4,5,6, construction7,8, automotive9, and marine10,11 industries due to its low density, high specific stiffness and strength, fatigue properties, and excellent corrosion resistance. Common synthetic fibers include carbon fibers, glass fibers, and aramid fibers12. Glass fiber was chosen for investigation in this paper. Compared to traditional steel, glass fiber reinforcement composite laminates (GFRPs) are lighter, with less than one-third of the density, but can achieve a higher specific strength than steel.
The preparation process of FRP includes vacuum-assisted resin transfer molding (VARTM)13, filament winding (FW)14, and prepreg molding, in addition to many other advanced fabrication processes15,16,17,18. Compared to other preparation processes, the wet hand lay-up/vacuum bag (WLVB) process has several advantages, including simple equipment requirements and uncomplicated process technology, and the products are not limited by size and shape. This process has a high degree of freedom and can be integrated with metal, wood, plastic, or foam.
The principle of the WLVB process is to apply greater forming pressure through vacuum bags to enhance the mechanical properties of the prepared laminates; the production technology of this process is easy to master, making it an economical and simple composite material preparation process. This process is completely manual, and it is greatly influenced by the skills of preparation personnel. Therefore, the products are prone to defects such as voids and uneven thickness, leading to unstable qualities and mechanical properties of the laminate. Hence, it is necessary to describe the WLVB process in detail, finely control steps, and quantify material proportion, in order to obtain a high stability of mechanical properties of laminates.
Most researchers have studied the quasi-static19,20,21,22,23 and dynamic behavior24,25,26,27,28, as well as the property modification29,30 of composite materials. The volume fraction ratio of fiber to matrix plays a crucial role in mechanical properties of FRP laminate. In an appropriate range, a higher volume fraction of fiber can improve the strength and stiffness of FRP laminate. Andrew et al.31 investigated the effect of fiber volume fraction on the mechanical properties of specimens prepared by the fused deposition modeling (FDM) additive manufacturing process. The results showed that when the fiber volume fraction was 22.5%, the tensile strength efficiency reached its maximum, and a slight improvement in strength was observed as the fiber volume fraction reached 33%. Khalid et al.32 studied the mechanical properties of continuous carbon fiber (CF)-reinforced 3D-printed composites with diverse fiber volume fractions, and the results showed that both tensile strength and stiffness were improved with the rise in fiber content. Uzay et al.33 investigated the effects of three fabrication methods-hand lay-up, compression molding, and vacuum bagging-on the mechanical properties of carbon fiber-reinforced polymer (CFRP). The fiber volume fraction and void of the laminates were measured, tensile and bending tests were conducted. The experiments showed that the higher the fiber volume fraction, the better the mechanical properties.
Voids are one of the most common defects in FRP laminate. Voids reduce the mechanical properties of composite materials, such as strength, stiffness, and fatigue resistance34. The stress concentration generated around the voids promotes the propagation of micro-cracks and reduces the interface strength between reinforcement and matrix. Internal voids also accelerate the moisture absorption of FRP laminate, resulting in interface debonding and performance degradation. Therefore, the existence of internal voids affects the reliability of composite and restricts their wide application. Zhu et al.35 investigated the influence of void content on the static interlaminar shear strength properties of CFRP composite laminates, and found that a 1% increase in void content ranging from 0.4% to 4.6% led to a 2.4% deterioration in interlaminar shear strength. Scott et al.36 presented the effect of voids on damage mechanism in CFRP composite laminates under hydrostatic loading using computed tomography (CT), and found that the number of voids is 2.6-5 times the number of randomly distributed cracks.
High-quality and reliable FRP laminates can be manufactured by using an autoclave. Abraham et al.37 manufactured low-porosity, high-fiber content laminates by placing a WLVB assembly in an autoclave with a pressure of 1.2 MPa for curing. Nevertheless, the autoclave is a large and expensive piece of equipment, resulting in considerable manufacturing costs. Although the vacuum-assisted resin transfer process (VARTM) has been in use for a long time, it has a limit in terms of the time cost, a more complicated preparation process, and more disposable consumables such as diversion tubes and diversion media. Compared with the WL process, the WLVB process compensates for insufficient molding pressure through a low-cost vacuum bag, absorbing excess resin from the system to increase the fiber volume fraction and reduce the internal pore content, thereby greatly improving the mechanical properties of the laminate.
This study explores the differences between the WL process and the WLVB process, and details the meticulous process of the WLVB process. The fiber volume content of laminates was calculated by the formula method, and the results showed that the fiber volume content of WL laminates was 42.04%, while that of WLVB laminates was 57.82%, increasing by 15.78%. The mechanical properties of laminates were characterized by tensile and impact tests. The experimental results revealed that with the WLVB process, the strength and modulus of the laminates were enhanced by 17.4% and 16.35%, respectively, and the specific absorbed energy was increased by 19.48%.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>breather fabric</td>
			<td>Easy composites</td>
			<td>BR180</td>
			<td></td>
		</tr>
		<tr>
			<td>drop-weight impact testing machine</td>
			<td>Instron</td>
			<td>9340</td>
			<td></td>
		</tr>
		<tr>
			<td>Epoxy matrix</td>
			<td>Axson Technologies</td>
			<td>5015/5015</td>
			<td></td>
		</tr>
		<tr>
			<td>glass fiber</td>
			<td>Weihai Guangwei Composites</td>
			<td>W-9311</td>
			<td></td>
		</tr>
		<tr>
			<td>non-porous release film</td>
			<td>Easy composites</td>
			<td>R240</td>
			<td></td>
		</tr>
		<tr>
			<td>Peel ply&#160;</td>
			<td>Sino Composite</td>
			<td>CVP200</td>
			<td></td>
		</tr>
		<tr>
			<td>perforated released film</td>
			<td>Easy composites</td>
			<td>R120-P3</td>
			<td></td>
		</tr>
		<tr>
			<td>test machine</td>
			<td>ZwickRoell</td>
			<td>250kN</td>
			<td></td>
		</tr>
		<tr>
			<td>vacuum film</td>
			<td>Easy composites</td>
			<td>GVB200</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring the mechanical properties of glass fiber reinforcement polymer composite laminates obtained by different fabrication processes

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the forming pressure, the mass fraction of fiber is reduced and lots of air bubbles are trapped inside, resulting in low-quality laminates (low stiffness and strength). The wet hand lay-up/vacuum bag (WLVB) process for the fabrication of composite laminates is based on the traditional wet hand lay-up process, using a vacuum bag to remove air bubbles and provide pressure, and then carrying out the heating and curing process. 
Compared with the traditional hand lay-up process, laminates manufactured by the WLVB process show superior mechanical properties, including better strength and stiffness, higher fiber volume fraction, and lower void volume fraction, which are all benefits for composite laminates. This process is completely manual, and it is greatly influenced by the skills of the preparation personnel. Therefore, the products are prone to defects such as voids and uneven thickness, leading to unstable qualities and mechanical properties of the laminate. Hence, it is necessary to finely describe the WLVB process, finely control steps, and quantify material ratios, in order to ensure the mechanical properties of laminates. 
This paper describes the meticulous process of the WLVB process for preparing woven plain patterned glass fiber reinforcement composite laminates (GFRPs). The fiber volume content of laminates was calculated using the formula method, and the calculated results showed that the fiber volume content of WL laminates was 42.04%, while that of WLVB laminates was 57.82%, increasing by 15.78%. The mechanical properties of the laminates were characterized using tensile and impact tests. The experimental results revealed that with the WLVB process, the strength and modulus of the laminates were enhanced by 17.4% and 16.35%, respectively, and the specific absorbed energy was increased by 19.48%.

Watch this Scientific Journal Video about Enhancing Fiber Composite Laminate Quality with the Wet Hand Lay-Up/Vacuum Bag Process at JoVE.com

Author Spotlight: Enhancing Fiber Composite Laminate Quality with the Wet Hand Lay-Up/Vacuum Bag Process 

This paper describes a fabrication process for fiber-reinforced polymer matrix composite laminates obtained using the wet hand lay-up/vacuum bag method.

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the ...

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1.8K Views.  Southern University of Science and Technology. Ons onderzoek richt zich op het verbeteren van de taaiheid van de interface en de verminderde weerstand van vezelcomposieten. We proberen de verminderde weerstand van vezelcomposieten te verbeteren door nanodeeltjes op te nemen. Een van de meest voorkomende uitdagingen bij de fabricage van vezelcomposieten is het gebrek aan herhaalbaarheid.Door nauwkeurige controle van de fabricagediepte en kwantificering van materiaalverhoudingen, kunnen we laminaten verkrijgen met zeer stabiele mecha...

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A Testing Platform for Durability Studies of Polymers and Fiber-reinforced Polymer Composites under Concurrent Hygrothermo-mechanical Stimuli

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs and condition-based maintenance. These materials are adopted in a wide range of engineering applications, from aircraft and ship structures, to bridges, wind turbine blades, biomaterials and biomedical implants. Polymers are viscoelastic materials, and their response may be highly nonlinear and thus make it challenging to predict and monitor their in-service performance. The laboratory-scale testing platform presented herein assists the investigation of the influence of concurrent mechanical loadings and environmental conditions on these materials. The platform was designed to be low-cost and user-friendly. Its chemically resistant materials make the platform adaptable to studies of chemical degradation due to in-service exposure to fluids. An example of experiment was conducted at RT on closed-cell polyurethane foam samples loaded with a weight corresponding to ~50% of their ultimate static and dry load. Results show that the testing apparatus is appropriate for these studies. Results also highlight the larger vulnerability of the polymer under concurrent loading, based on the higher mid-point displacements and lower residual failure loads. Recommendations are made for additional improvements to the testing apparatus.

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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Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

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A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers.

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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.
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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.

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Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

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Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior

The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth&#39;s magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a uniform electromagnetic field to fresh mortar containing short steel fibers, whereby the short steel fibers were driven to rotate in alignment with the magnetic field. The degree of alignment of steel fibers in hardened ASFRC was assessed both by counting steel fibers in fractured cross-sections and by X-ray computed tomography analysis. The results from the two methods show that the steel fibers in ASFRC were highly aligned while the steel fibers in non-magnetically treated composites were randomly distributed. The aligned steel fibers had a much higher reinforcing efficiency, and the composites, therefore, exhibited significantly enhanced flexural strength and toughness. The ASFRC is thus superior to SFRC in that it can withstand greater tensile stress and more effectively resist cracking.

This protocol describes an approach for manufacturing aligned steel fiber reinforced cementitious composite by applying a uniform electromagnetic field. Aligned steel fiber reinforced cementitious composite exhibits superior mechanical properties to ordinary fiber reinforced concrete.

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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.

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

One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. Customized channel layout designs are necessary for specific functions and integrated performance of microfluidic devices in numerous biomedical and chemical applications (e.g., cell culture, biosensing, chemical synthesis, and liquid handling). Owing to the nature of molding approaches using silicon wafers with photoresist layers patterned by photolithography as master molds, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights. Typically, channels with multiple heights or different geometric sections are designed to possess particular functions and to perform in various microfluidic applications (e.g., hydrophoresis is used for sorting particles and in continuous flows for separating blood cells6,7,8,9). Therefore, a great deal of effort has been made in constructing channels with various sections through multiple-step approaches like photolithography using several photoresist layers and assembly of different PDMS thin sheets. Nevertheless, such multiple-step approaches usually involve tedious procedures and extensive instrumentation. Furthermore, the fabricated devices may not perform consistently and the resulted experimental data may be unpredictable. Here, a one-step approach is developed for the straightforward fabrication of microfluidic channels with different geometric cross sections through PDMS sequential wet etching processes, that introduces etchant into channels of planned single-layer layouts embedded in PDMS materials. Compared to the existing methods for manufacturing PDMS microfluidic channels with different geometries, the developed one-step approach can significantly simplify the process to fabricate channels with non-rectangular sections or various heights. Consequently, the technique is a way of constructing complex microfluidic channels, which provides a fabrication solution for the advancement of innovative microfluidic systems.

Several methods are available for the fabrication of channels of non-rectangular sections embedded in polydimethylsiloxane microfluidic devices. Most of them involve multistep manufacturing and extensive alignment. In this paper, a one-step approach is reported for fabricating microfluidic channels of different geometric cross sections by polydimethylsiloxane sequential wet etching.

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. ...

Design and Fabrication of an Optical Fiber Made of Water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with ...

A Random-displacement Measurement by Combining a Magnetic Scale and Two Fiber Bragg Gratings

Long-distance displacement measurements using optical fibers have always been a challenge in both basic research and industrial production. We developed and characterized a temperature-independent fiber Bragg grating (FBG)-based random-displacement sensor that adopts a magnetic scale as a novel transferring mechanism. By detecting shifts of two FBG center wavelengths, a full-range measurement can be obtained with a magnetic scale. For identification of the clockwise and counterclockwise rotation direction of the motor (in fact, the direction of movement of the object to be tested), there is a sinusoidal relationship between the displacement and the center wavelength shift of the FBG; as the anticlockwise rotation alternates, the center wavelength shift of the second FBG detector shows a leading phase difference of around 90&#176; (+90&#176;). As the clockwise rotation alternates, the center wavelength shift of the second FBG displays a lagging phase difference of around 90&#176; (-90&#176;). At the same time, the two FBG-based sensors are temperature independent. If there is some need for a remote monitor without any electromagnetic interference, this striking approach makes them a useful tool for determining the random displacement. This methodology is appropriate for industrial production. As the structure of the whole system is relatively simple, this displacement sensor can be used in commercial production. In addition to it being a displacement sensor, it can be used to measure other parameters, such as velocity and acceleration.

A protocol to create a full-range linear displacement sensor, combining two packaged fiber Bragg grating detectors with a magnetic scale, is presented.

Long-distance displacement measurements using optical fibers have always been a challenge in both basic research and industrial production. We developed ...

Measurement of Dynamic Force Acted on Water Strider Leg Jumping Upward by the PVDF Film Sensor

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, with its peak locomotion speed reaching 150 cm/s. First of all, we observed the microstructure and hierarchy of water strider legs using the scanning electron microscope. On the basis of the observed morphology of the legs, a theoretical model of the detachment from water surface was established, which explained water striders' capability to slide on water surface effortlessly in terms of energy reduction. Secondly, a dynamic force measurement system was devised using the PVDF film sensor with excellent sensitivity, which could detect the whole interaction process. Subsequently, a single leg in contact with water was pulled upward at different speeds, and the adhesion force was measured at the same time. The results of the departing experiment suggested a deep understanding of the fast jumping of water striders.

The protocol here is dedicated to investigating the free and quick maneuvering of water strider on water surface. The protocol includes observing the microstructure of legs and measuring the adhesion force when departing from water surface at different speeds.

This study aimed to make an explanation for the phenomenon in nature that water strider usually jumps or glides on the water surface easily but quickly, ...

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes

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