Name: preparation of aligned steel fiber reinforced cementitious composite and its flexural behavior
Uploaded: 2018-06-27T12:30:00.000+00:00
Duration: 11 min 7 s
Description: Watch this Scientific Journal Video about Preparation of Aligned Steel Fiber Reinforced Cementitious Composite and Its Flexural Behavior at JoVE.com

The authors gratefully acknowledge financial supports from the National Nature Science Foundation of China (Grant No. 51578208), Hebei Provincial Nature Science Foundation (Grant No. E2017202030 and E2014202178), and Key Project of University Science and Technology Research of Hebei Province (Grant No. ZD2015028).

1. Solenoid Magnetic Field Setup
NOTE: The magnetic field is generated by a solenoid with a hollow chamber. The setup is a polybutylene terephthalate (PBT) board solenoid skeleton coiled with 4-6 layers of enamel insulated copper wire and wrapped with a plastic insulating layer for protection (Figure 1). After connecting the coil to DC, the current in the coil creates a uniform electromagnetic field within the solenoid chamber with a fixed direction and constant magnetic induction intensity. Use the magnetic field to align steel fibers in fresh mortar and prepare the ASFRC specimens. In this study, we prepared 150&#215;150&#215;550 mm prism specimens using a solenoid with a chamber size of 250&#215;250&#215;750 mm.
<ol>
	<li>Correlate the magnetic induction intensity to the electrical current of the solenoid.
	<ol>
		<li>Connect the solenoid to DC and apply current from 0 to 10 A with a step length of 1 A. Measure and record the magnetic induction intensity in the solenoid chamber using a tesla meter.</li>
		<li>Plot the magnetic induction intensity-current curve (Figure 2), which will be used in later steps to determine the necessary current of the solenoid. 
		NOTE: Carefully follow electrical safety procedures when connecting the solenoid to the power source and in all other operation procedures relevant to electrical power.</li>
	</ol>
	</li>
</ol>
2. Workability of Fresh Mortar
<ol>
	<li>Prepare three mortar mixes with steel fiber volume fractions 0.8%, 1.2%, and 2.0%, respectively (Table 1). The three mixes have the same matrix composition with a water to cement to sand ratio of 0.42:1:2. According to the mix ratio, weigh 0.5 kg of cement, 1.0 kg of sand, and 0.21 kg of water for workability tests.</li>
	<li>Add water to the mortar mixer first. Then add the cement. Mix the water and cement for 30 s. Then mix for another 30 s, and during this 30 s of mixing, gradually add sand to the mixer. Then mix for another 60 s.</li>
	<li>Test the sinking depth of the mixture using a sinking depth meter following the Chinese standard for test method of performance on building mortar (JGJ/T70-2009)19.</li>
	<li>Repeat steps 2.2 and 2.3, adjusting the dosage of the superplasticizer until the sinking depth falls into the 50-100 mm range. Record the dosage of the superplasticizer that produces the desired workability and supplement it as part of the mix proportion in Table 1. Also test the specific density of the fresh mortar after the workability is achieved. The optimized dosage of a polycarboxylate superplasticizer from the aforementioned tests is 0.10% (mass ratio to cement), and the specific density of fresh mortar is 2186 kg/m3.</li>
	<li>Test the viscosity of the fresh mortar using a co-axial rotational mortar rheometer (Figure 3). The rheometer has a water bath that can maintain the temperature of the sample container at 20 &#176;C.
	<ol>
		<li>Put 300 mL of fresh mortar mixed within the previous 5 min into the sample container.</li>
		<li>Begin the viscosity test. The probe gradually drops into the fresh mortar in the container, and the container begins to rotate. As the fresh mortar moves within the rotating container, it applies a shear force on the probe. In the process, the rheometer records the shear stress and shear rate and plots the curve of shear stress to shear rate. The slope of the curve is the viscosity of the mortar20,21. In this investigation, the viscosity of the fresh mortar from tests is 0.82 Pas.</li>
	</ol>
	</li>
</ol>
3. Specimen Preparation
<ol>
	<li>Determine the magnetic induction intensity of the magnetic field and the current of the solenoid.
	<ol>
		<li>Using the viscosity of the cement mortar determined in step 2.5.2, calculate the magnetic induction intensity of the magnetic field required for aligning steel fibers in cement mortar using Equation (1):13 
		<img alt="Equation 1" src="/files/ftp_upload/56307/56307eq1v2.jpg" /> (1) 
		where B is magnetic induction intensity,&#160;&#951; is the viscosity of fresh mortar, lf is the length of steel fiber, m is the mass of an individual steel fiber, rf is the radius of steel fibers, &#956; is the permeability of steel fibers, &#956;0 is the permeability of the vacuum, &#916;t is time interval, and &#945;(t+&#916;t) is the angular acceleration at the next time interval. According to the viscosity and the parameters of the steel fiber used in the tests, the required magnetic induction intensity is 9.83 mT.</li>
		<li>Determine the electrical current of the solenoid required to create a sufficient magnetic induction intensity according to Figure 2 or Equation (2):14 
		<img alt="Equation 2" src="/files/ftp_upload/56307/56307eq2v2.jpg" /> (2) 
		where I is the required current, N is the number of solenoid turns, and L is the length of the solenoid. 
		Using Equation (2), the required current is 8.3 A, while from Figure 2 it is about 8.5 A.</li>
	</ol>
	</li>
	<li>Prepare ASFRC specimens
	<ol>
		<li>Use a 15 L mortar mixer to mix fresh mortar. For each batch, mix 7.5 L of mortar according to the mix proportions listed in Table 1. Table 1 denotes the ASFRC mixes as A-Vf, where A indicates that the steel fibers are aligned and Vf indicates the volume fraction of steel fiber. Accordingly, the SFRC mixes are denoted, for comparison, as R-Vf, where R indicates that the steel fibers are randomly distributed. The SFRC mixes are not listed in Table 1 but have the same proportions as ASFRC.</li>
		<li>Weigh the raw materials and mix the steel fiber reinforced cement mortar following routine procedures.</li>
		<li>Pour the fresh mortar into a plastic mold with clear size of 150&#215;150&#215;550 mm. Cast the specimens promptly after mixing to avoid losing workability. It takes around 25 min to cast one ASFRC prism from the contact between cement and water.</li>
		<li>Move the mold onto a compacting table, and switch on the compacting table for 30 s. Add more mortar as needed to ensure that that the mold is completely filled.</li>
		<li>Put the mold into the chamber of the solenoid.</li>
		<li>Switch on the solenoid and compacting table for 50 s. 
		NOTE: For ordinary concrete the reasonable compacting time is around 60-120 s. In this test, it is attempted to control the total compacting time within this range. Longer compacting time may improve the alignment of steel fibers; however, it may cause over compacting and consequently the segregation (the sinking of steel fibers and coarse aggregates if there are). Less compacting time may cause poor alignment of steel fiber and unconsolidated concrete.</li>
		<li>Switch off the compacting table.</li>
		<li>Switch off the solenoid after the compacting table has stopped completely.</li>
		<li>Gently take out the mold from the solenoid and smooth the top surface of the mortar with a trowel. Avoid disturbing the steel fibers near the top surface.</li>
	</ol>
	</li>
	<li>For each mix, prepare three electromagnetically treated specimens (following steps 3.2.2-3.2.9) and three non-electromagnetically treated specimens (following steps 3.2.2-3.2.4 and 3.2.9). In the preparation of non-electromagnetically treated specimens, the total compacting time was 80 s&#8212;the same as that in the preparation of electromagnetically treated specimens.</li>
	<li>Leave the specimens indoors and in their molds for 24 h. Then demold and cure the specimens in a fog room until they are used for mechanical tests.</li>
</ol>
4. Three-Point Bending Test
<ol>
	<li>After 28 days, take out the specimens from the curing room and mark the positions for loading (A), supports (B), mid-span deflection (C), and LVDT fixing points (D) (Figure 4).</li>
	<li>Place the specimen on the three-point bending test rig (Figure 4) of the MTS test machine and fix a LVDT to the mid-span using a LVDT holder on each side surface of the specimen (Figure 4).</li>
	<li>Connect the LVDT to a datalog. Then set the data acquisition frequency on the control PC of the test machine.</li>
	<li>Gradually raise the specimen by raising the bottom supports so that the upper loading cell of the test machine is very close to, but not touching, the top surface of the specimen.</li>
	<li>Zero the initial load, mid-span deflection (LVDT), and displacement (load cell) values.</li>
	<li>Start the test and apply a three-point bending load to the specimen with a displacement control at a speed of 0.2 mm/min. Record the full history of the loading and mid-span deflection of the specimen.</li>
	<li>Watch the load and deformation of the specimen. After peak value, when the displacement is greater than 30 mm, stop the test. Usually, the specimen is cracked and the load is less than 1.0 kN.</li>
	<li>Repeat steps 4.1-4.7 to test all specimens.</li>
</ol>
5. Steel Fiber Orientation Analysis
<ol>
	<li>Count the number of steel fibers on the fractured section.
	<ol>
		<li>Separate the specimens into two portions at the cracked section.</li>
		<li>Measure and record the orientation of the steel fibers on the fractured cross section of the cement mortar specimen. The orientation is the angle between a steel fiber and the axis of the specimen. Because manually measuring the orientations of steel fibers is difficult and can produce inaccurate measurements, orientations can be categorized as one of six angle ranges: 0 - 15 &#176;, 15 - 30 &#176;, 30 - 45 &#176;, 45 - 60 &#176;, 60 - 75 &#176; and 75 - 90 &#176;. Record the number of steel fibers in each group, and then calculate the average fiber orientation efficiency factor of the specimen using Equation (3): 
		<img alt="Equation 3" src="/files/ftp_upload/56307/56307eq3v2.jpg" /> (3) 
		where &#951;&#952; is the average orientation efficiency factor of the steel fibers, lf is the length of an individual steel fiber, n is the total number of steel fibers on the cracked section, and &#952;i is the angle between a steel fiber and direction of the magnetic field applied to the specimen (in the calculation, the middle value of the angle range is adopted for all steel fibers in each group).</li>
	</ol>
	</li>
	<li>Perform X-ray computed tomography analysis.
	<ol>
		<li>Cut a 75 mm cube from each mortar specimen.</li>
		<li>Perform the X-ray scanning of the cube using an X-ray computed tomography system. Place a specimen on the test platform and begin scanning. The specimen rotates 360 &#176; gradually and the machine records the attenuation of the X-rays caused by the specimen at each rotating step. The computed tomography system generates a three-dimensional digital structure of the cube.</li>
		<li>Identify the steel fibers in the digital cube structure by black and white binary processing. Then obtain the digital image describing the distribution of steel fibers.</li>
		<li>Determine the coordinates of all steel fibers by image analysis.</li>
		<li>Calculate the orientation of each steel fiber according to its coordinates.</li>
		<li>Calculate the orientation efficiency factor of the fibers using Equation (3).</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The electromagnetic solenoid developed in this study has a chamber measuring 250&#215;250&#215;750 mm and cannot accommodate the full size structural elements. Although the size of the chamber limits the application of the setup, the concept and protocol proposed in this paper will inspire the further development of a full size setup for manufacturing ASFRC elements, particularly precast elements.
Achieving an appropriate viscosity of fresh mortar is essential factor for controlling the qualit...

Incorporating steel fibers into concrete is an effective way to overcome the inherent weakness of brittleness and to improve the tensile strength of concrete1. During the past decades, steel fiber reinforced concrete has been extensively investigated and widely used in the field. Steel fiber reinforced concrete is superior to concrete in terms of cracking resistance, tensile strength, fracture toughness, fracture energy, etc.2 In steel fiber reinforced concrete, steel fibers are randomly dispersed, thereby uniformly dispersing the reinforcing efficiency of the fibers in every direction. However, under certain loading conditions, only some of the steel fibers in concrete contribute to the performance of the structural elements because the reinforcing efficiency of the fibers requires that they be aligned with the principle tensile stresses in the structure. For instance, when using steel fiber reinforced concrete containing randomly distributed steel fibers to prepare a beam, some of the steel fibers, especially those parallel to the direction of the principal tensile stress, will make major contribution to reinforcing efficiency, while those perpendicular to the direction of the principal tensile stress will make no contribution to reinforcing efficiency. Consequently, finding an approach to align the steel fibers with the direction of the principal tensile stress in concrete is necessary to achieve the highest reinforcing efficiency of the steel fibers.
The orientation efficiency factor, defined as the ratio of the projected length along the direction of the tensile stress to the actual length of fibers, is usually used to indicate the efficiency of the reinforcement of steel fibers3,4. According to this definition, the orientation efficiency factor of the fibers aligned with the direction of the tensile stress is 1.0; that of the fibers that are perpendicular to the tensile stress is 0. Inclined fibers have an orientation efficiency factor between 0 and 1.0. The analytical results show that the orientation efficiency factor of randomly distributed steel fibers in concrete is 0.4054, while that from tests of ordinary steel fiber reinforced concrete is in the range of 0.167 to 0.5005,6. Evidently, if all the short steel fibers in concrete are aligned and have the same orientation as the tensile stress, the steel fibers will have the highest reinforcing efficiency and the specimens will have the optimum tensile behavior.
Some successful attempts to prepare aligned steel fiber reinforced concrete have been conducted since 1980s. In 1984, Shen7 applied an electromagnetic field to the bottom layer of steel fiber reinforced cementitious composite (SFRC) beams during casting, and X-ray detection analysis revealed that steel fibers were well aligned. In 1995, Bayer8 and Arman9 patented the approach for preparing aligned steel fiber reinforced concrete using a magnetic field. Yamamoto et al.10 considered the orientation of steel fibers in concrete to be mainly influenced by the casting approach and attempted to obtain aligned steel fiber reinforced concrete by keeping fresh concrete flowing into the formwork from a constant direction. Xu11 attempted to align steel fibers in shotcrete by spraying steel fibers from a constant direction. Rotondo and Wiener12 sought to make concrete poles with aligned long steel fibers by centrifugal casting. These experimental studies reveal that aligned steel fiber reinforced concrete has significant advantages over randomly distributed steel fiber reinforced concrete.
Recently, Michels et al.13 and Mu et al.14 have successfully developed a group of aligned steel fiber reinforced cementitious composites (ASFRCs) using electromagnetic fields. In these studies, various solenoids were made to provide a uniform magnetic field for aligning steel fibers in mortar specimens of different sizes. The solenoid has a hollow cuboid chamber, which can accommodate specimens of predefined sizes. When the solenoid is connected to direct current (DC), a uniform magnetic field is created in the chamber with a fixed orientation, which aligns with the axis of the solenoid. According to the principle of electromagnetics15, magnetic fields can drive ferromagnetic fibers to rotate and align in fresh mortar. Appropriate workability of the mortar is critical for allowing steel fibers to rotate in fresh mortar. A high viscosity may cause difficulty in the alignment of the steel fibers in the mortar, while low viscosity may lead to the segregation of fibers.
This paper describes the details of the preparation of ASFRC specimens and tests the flexural properties of ASFRC and SFRC. It is expected that ASFRC has a higher flexural strength and toughness than SFRC. Thus, ASFRC potentially has advantages over SFRC in withstanding tensile stress and resisting cracking if used as cover concrete, pavement, etc.
Using the fractured specimens after flexural tests, the orientation of the steel fibers in the specimens is investigated by observing the fractured cross sections and utilizing X-ray scanning computed tomography analysis16,17,18. The mechanical properties of ASFRCs, including their flexural strength and toughness, are reported and compared with those of non-electromagnetically treated SFRCs.

<table><tbody><tr><td>Cement</td><td>Tangshan Jidong Cement Co., Ltd.</td><td>P&amp;times;O 42.5</td><td>Oridnary Portland Cement</td></tr><tr><td>Sand</td><td></td><td>River sand</td><td>Fineness modulus is 2.4</td></tr><tr><td>Superplasticizer</td><td>Subote New Materials Co., Ltd.</td><td>PCA-III</td><td>Polycarboxylated type, water reducing ratio is 35%</td></tr><tr><td>Steel fiber</td><td>Tianjin Hengfeng Xuxiang New Metal Materials Co., Ltd.</td><td>Round straight</td><td>Diameter 0.5mm, length 25mm</td></tr></tbody></table>

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.

The flexural strengths of ASFRCs and SFRCs determined from three-point bending tests are shown in Figure 5. The flexural strengths of ASFRCs are higher than those of SFRCs for all fiber dosages. The flexural strengths of ASFRCs were 88%, 71%, and 57% higher than those of SFRCs at the fiber volume fractions of 0.8%, 1.2%, and 2.0%, respectively. These results imply&#160;that the aligned steel fiber reinforces the cementitious matrix more effectively than rando...

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

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 ...

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11.0K Views.  Hebei University of Technology. 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.

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

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 ...

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they can delay or even prevent debonding failure. However, a major concern faced by designers is the premature failure of the anchors due to stress concentration. Poor installation quality and preparation of the clearance holes can result in stress concentration that provokes this premature failure. This paper deals with an installation method that aims to reduce the impact of the stress concentration and to provide a proper quality control of the preparation of the drill hole. The method involves three parts: the drilling and cleaning of the holes, the smoothing of the hole edges with a customized drill bit, and the installation of the anchor itself, including the impregnation of the anchor dowel and its insertion. Anchor fans (the free length of the spikes) are then bonded to the external FRP reinforcement. For the end anchorage, and in the case of reinforcements with multiple plies, it is recommended that the anchor fan be inserted between two plies to assist the stress-transfer mechanism. 
The proposed procedure is complemented with a design approach for spike anchors, based on an extensive database. It is proposed that the design follow a number of steps, namely: selection of the anchor diameter and subsequent tensile strength of the connector (that is to say, the anchor before fanning out the free end), evaluation of the reduction in the tensile strength due to bending, provision of enough embedment to prevent slippage failure, and consideration of the number and spacing of anchors for a given reinforcement. In this sense, it should be noted that further research is needed in order to obtain a general expression for the contribution of spike anchors to overall bond strength of FRP reinforcements.

This manuscript presents a method for controlling the quality of installation for spike anchors designed to delay delamination of externally bonded fiber reinforced polymers. The protocol includes the preparation of the drill hole and the insertion process. The most influential parameters on the efficiency of the anchors are discussed.

Fiber reinforced polymer (FRP) anchors are a promising way to enhance the performance of externally-bonded FRPs applied to existing structures, as they ...

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, ...

Determination of the Mechanical Properties of Flexible Connectors for Use in Insulated Concrete Wall Panels

This document contains recommendations for performing a non-standard, double-shear test suitable for both continuous and discrete insulated concrete sandwich wall panels (ICSWPs). Such a standardized test does not exist, but several iterations of this and similar tests have been performed in the literature to varying degrees of success. Further, the tests in the literature are rarely-if ever-described in detail or discussed at length with respect to the testing, data analysis, or safety procedures. A test specimen configuration is recommended herein, and variations are discussed. Important mechanical properties are identified from the load versus displacement data, and their extraction is detailed. The use of test data for design, such as for determining the stiffness of the connectors, is briefly demonstrated to show how ICSWP deflection and cracking behavior may be calculated. The strength behavior of panels may be determined using the full load versus displacement curve or only the maximum connector strength. Shortcomings and unknowns are acknowledged, and significant future work is delineated.

We propose a testing protocol that can be combined with widely available analytical methods to assess the mechanical properties of shear connectors for use in the design of insulated concrete wall panels to predict full-scale insulated panel behavior.

This document contains recommendations for performing a non-standard, double-shear test suitable for both continuous and discrete insulated concrete ...

Fabrication and Mechanical Property Assessment of Fiber Composite Laminates

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%.

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.

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

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 ...

JoVE Science Education

Structural Engineering

Ceramic-matrix Composite Materials and Their Bending Properties

Source: Sina Shahbazmohamadi and <a href="https://www.jove.com/author/Peiman_Shahbeigi-Roodposhti">Peiman Shahbeigi-Roodposhti-Roodposhti</a>, School of Engineering, University of Connecticut, Storrs, CT
Bones are composites, made of a ceramic matrix and polymer fiber reinforcements. The ceramic contributes compressive strength, and the polymer provides tensile and flexural strength. By combining ceramic and polymer materials in different amounts, the body can create unique materials tailored for a specific application. As biomedical engineers, having the ability to replace and replicate bone due to disease or traumatic injury is a vital facet of medical science.
In this experiment we will create three different ceramic-matrix composites with plaster of Paris (which is a calcium sulfate compound), and allow them to undergo three-point bending test in order to determine which preparation is the strongest. The three composites are as follows: one comprised only of plaster of Paris, one with chopped glass shards mixed in a plaster matrix and lastly a plaster matrix with a fiberglass network embedded within it.

Bending Strength and 3-Point Bending Test of Ceramic Materials

Source: Sina Shahbazmohamadi and Peiman Shahbeigi-Roodposhti-Roodposhti, School of Engineering, University of Connecticut, Storrs, CT
Bones are ...

Materials Engineering

Tests of Hardened Concrete in Tension

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
In a previous laboratory focused on concrete in compression, we observed that concrete can withstand very large stresses under uniaxial compressive forces. However, the failures observed were not compressive failures but failures along shear planes where maximum tensile forces occur. Thus, it is important to understand the behavior of concrete in tension and particularly its maximum strength as that will govern both its ultimate and service behavior. From the ultimate standpoint, combinations of tension and shear stresses will lead to cracking and immediate and catastrophic failure. For that reason, concrete is seldom if ever used in an unreinforced condition in structural applications; most concrete members will be reinforced with steel so that these cracks can be stopped and the crack widths limited. The latter is important from the serviceability standpoint because controlling crack widths and distribution is the key to durability, as this will impede deicing salts and similar chemicals from penetrating and corroding the reinforcing steel.
The objectives of this experiment are threefold: (1) to conduct tensile split cylinder tests to determine concrete tensile strength, (2) to conduct beam tests to determine concrete tensile strength, and (3) to demonstrate the influence of steel reinforcement on behavior by comparing the behavior of lightly reinforced beam with an unreinforced one.

Split Tension Test and Beam Tension Test for Hardened Concrete

Source:&#160;Roberto Leon, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA
In a previous laboratory focused on concrete ...

Strength of Cement

Strength tests for cement are not performed directly on neat cement paste due to difficulty in obtaining consistent, reliable specimens. Instead, cement is typically tested in the form of cement-sand mortar.
For compressive strength tests, ASTM C 109-05 standards prescribe a cement-sand mix ratio of 1:2.75 and a water/cement ratio of 0.485 for making 2-inch cubes. These cubes are mixed, cast, and cured in saturated lime water at 23&#176;C until testing. Flexural strength testing, outlined in ASTM C 348-02, uses prisms measuring 1.5 x 1.57 x 6.3 inches that are simply supported and loaded at mid-span. Another method to determine the compressive strength of cement is the modified cube test, detailed in ASTM C 349-02. This test uses sections of failed flexural prisms to test compression.
ASTM C150 specifies minimum compressive strength values for various types of cement at different stages of aging. The British Standard BS EN 196-1: 2005 categorizes cement into strength classes, such as N for normal and R for rapid hardening properties.

Wytrzymałość cementu

The ability of cement to resist compressive forces is known as its compressive strength, while its ability to endure bending forces is referred to as its ...

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

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

Installation Method to Enhance Quality Control for Fiber Reinforced Polymer Spike Anchors

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

Determination of the Mechanical Properties of Flexible Connectors for Use in Insulated Concrete Wall Panels

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

Tension Test of Fiber-Reinforced Polymeric Materials

Ceramic-matrix Composite Materials and Their Bending Properties

Tests of Hardened Concrete in Tension

Wytrzymałość cementu

Wytrzymałość cementu