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 proces...

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><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&amp;nbsp;</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%.

Table 1 shows the fiber volume fraction, average thickness, and fabrication process of the samples. The G8-WLVB and G8-WL represent the laminates consisting of 8-ply glass fabric manufactured by wet hand lay-up with and without the vacuum bag process, respectively. Obviously, with the vacuum bag assistance, laminates have an increase of 15.78% in fiber volume fraction, as well as an reduction of 16.27% in average thickness.
Strain-stress curves obtained by the tensile test of ...

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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1.9K Views.  Southern University of Science and Technology. This paper describes a fabrication process for fiber-reinforced polymer matrix composite laminates obtained using the wet hand lay-up/vacuum bag method.

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

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.

The durability of polymers and fiber-reinforced polymer composites under service condition is a critical aspect to be addressed for their robust designs ...

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).

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

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step ...

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 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 ...

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 ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

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.

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 ...

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 ...

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to diversify the fiber choices in the United States body armor market, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and the more conventional PPTA were introduced. Little is known regarding the long-term stability of these fibers, but as condensation polymers, they are expected to have potential sensitivity to moisture and humidity. Therefore, characterizing the strength of the materials and understanding their vulnerability to environmental conditions is important for evaluating their use lifetime in safety applications. Ballistic resistance and other critical structural properties of these fibers are predicated on their strength. To accurately determine the strength of the individual fibers, it is necessary to disentangle them from the yarn without introducing any damage. Three aramid-based copolymer fibers were selected for the study. The fibers were washed with acetone followed by methanol to remove an organic coating that held the individual fibers in each yarn bundle together. This coating makes it difficult to separate single fibers from the yarn bundle for mechanical testing without damaging the fibers and affecting their strength. After washing, fourier transform infrared (FTIR) spectroscopy was performed on both washed and unwashed samples and the results were compared. This experiment has shown that there are no significant variations in the spectra of poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide) (PBIA-co-PPTA1) and PBIA-co-PPTA3 after washing, and only a small variation in intensity for PBIA. This indicates that the acetone and methanol rinses are not adversely affecting the fibers and causing chemical degradation. Additionally, single fiber tensile testing was performed on the washed fibers to characterize their initial tensile strength and strain to failure, and compare those to other reported values. Iterative procedural development was necessary to find a successful method for performing tensile testing on these fibers.

The primary goal of the study is to develop a protocol to prepare consistent specimens for accurate mechanical testing of high strength copolymer aramid fibers, by removing a coating and disentangling the individual fiber strands without introducing significant chemical or physical degradation.

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to ...

Chemistry

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, ...

Tension Test of Fiber-Reinforced Polymeric Materials

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Fiber-reinforced polymeric materials (FRP) are composite materials that are formed by longitudinal fibers embedded in a polymeric resin, thereby creating a polymer matrix with aligned fibers along one or more directions. In its simplest form, the fibers in FRP materials are aligned in an orderly, parallel fashion, thus imparting orthotropic material characteristics, meaning that the material will behave differently in the two directions. Parallel to the fibers, the material will be very strong and/or stiff, whereas perpendicular to the fibers will be very weak, as the strength can only be attributed to the resin instead of the whole matrix.
An example of this unidirectional configuration is the commercially available FRP reinforcing bars, which mimic the conventional steel bars used in reinforced concrete construction. FRP materials are used both as stand-alone structures such as pedestrian bridges and staircases, and also as materials to strengthen and repair existing structures. The thin, long plates are often epoxied to existing concrete structures to add strength. In this case, the FRP bars act as external reinforcement. The FRP bars and plates are lighter and more corrosion resistant, so they are finding applications in bridge decks and parking garages, where de-icing slats lead to rapid deterioration of conventional bars.
In this laboratory exercise, the tensile behavior of a unidirectional specimen will be studied, with emphasis on its ultimate strength and deformation capacity. The behavior of the specimen is expected to be elastic until failure, which is expected to occur in a sudden and explosive manner. This behavior should be contrasted with those of ductile steels, which exhibit extensive deformation capacity and strain hardening before failure.

Uniaxial Tension Test of Fiber-Reinforced Polymeric Materials

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
Fiber-reinforced polymeric materials (FRP) are ...