The authors would like to acknowledge the support of Ten Cate Advanced Materials in the form of free material supply to the work described in this paper.

1. Specimen Cutting and Preparation for Ultrasonic Welding
<ol>
	<li>Cut rectangular samples measuring 25.4 mm x 101.6 mm from a larger thermoplastic composite laminate using a cutting technique that prevents delamination of the edges of the samples (e.g., diamond-saw or water-jet cutting). 
	Note: The dimensions of the samples are based on ASTM D 1002 standard.
	<ol>
		<li>Since strength of the welded joints depends on the fiber orientation on the surfaces to be welded10, take care to cut all the samples in the same orientation.</li>
	</ol>
	</li>
	<li>After cutting, dry samples in an oven as per the manufacturer&#39;s recommendations in case the thermoplastic resin tends to absorb moisture (e.g., 6 hr at 135 &#176;C for six-layer carbon fiber reinforced polyetherimide, CF/PEI, samples).</li>
	<li>Cut flat energy directors made out of neat thermoplastic film (same resin as the matrix in the composite) to size (approximately 26 mm x 26 mm) with a thickness of at least 0.25 mm. If necessary, dry the energy director following manufacturer&#39;s recommendations (e.g., 1 hr at 135 &#176;C for PEI energy director).</li>
	<li>Before welding, inspect specimens one by one for delaminated corners and discard if necessary. Clean them using a degreaser and a cotton cloth. Clean the flat energy directors following the same procedure.</li>
</ol>
2. Ultrasonic Welding of Single Lap Shear Coupons
Note: A micro-processor controlled ultrasonic welder able to weld at constant amplitude is used in this step. The welder outputs process data, such as dissipated power and displacement of the sonotrode versus time to data acquisition software in a computer. A custom-built jig designed and manufactured to accurately position and clamp single lap shear samples during ultrasonic welding is used in this step (see Figure 1).
<img alt="Figure 1" src="/files/ftp_upload/53592/53592fig1.jpg" /> 
Figure 1. Ultrasonic welder and custom-built welding setup used in this study. 1: sonotrode, 2: sliding platform, 3: clamp for the upper specimen (attached to 2), and 4: clamp for the lower specimen (Reprinted from reference 4 with permission from Elsevier.) <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol>
	<li>Fill out a logbook sheet before each welding experiment.
	<ol>
		<li>Take note of the following parameters: RT and humidity, welding setup reference, sonotrode type, sample number and materials, width and thickness of top and bottom samples, and thickness of the energy director.</li>
	</ol>
	</li>
	<li>Turn on the ultrasonic welder and computer. Start the data acquisition software and open a new session.</li>
	<li>If not already in place, change the sonotrode to a cylindrical sonotrode with a diameter of 40 mm so that its bottom surface completely covers the welding area. 
	Note: A different shape of sonotrode can be used, but its bottom surface should not be smaller than the welding area.</li>
	<li>Position and fixate specimens and energy director into the welding jig (see Figure 1).
	<ol>
		<li>Attach a flat energy director to the bottom specimen with adhesive tape so that it covers a slightly larger area than the area to be welded (12.7 mm x 25.4 mm).</li>
		<li>Place the bottom sample into the jig and clamp it by tightening the top screw.</li>
		<li>Tape the other end of the energy director to the base of the setup so that it stays in place during the process.</li>
		<li>Place the upper sample into the clamp, align it and tighten the top screw.</li>
		<li>Position the clamp for the top sample into the sliding platform and tighten both screws.</li>
		<li>Before proceeding further, tighten all four screws once more.</li>
	</ol>
	</li>
	<li>Determine the optimum duration of the vibration phase based on the displacement of the sonotrode to achieve the highest weld strength, as described in steps 2.5.1 to 2.5.8. 
	Note: An optimum duration of the vibration phase is determined for each desired combination of welding force and vibration amplitude.
	<ol>
		<li>Set the ultrasonic welder to differential displacement-control mode.</li>
		<li>Input welding force and vibration amplitude into the ultrasonic welder (for example, 300 N and 86.2 &#956;m). 
		Note: For this ultrasonic welder, 86.2 &#956;m corresponds to the peak-to-peak vibration amplitude. In the machine settings, it is expressed as half this value, 43.1 &#956;m.</li>
		<li>Input the sonotrode displacement, or travel, at the end of the vibration phase as a value equal to the initial thickness of the energy director (for example, 0.25 mm).</li>
		<li>Input solidification force and time into the ultrasonic welder (for example, 1,000 N and 4,000 msec).</li>
		<li>When ready, put on soundproof headphones and start the ultrasonic welding process.</li>
		<li>After the completion of the process, take note of the following output parameters: welding distance, maximum power, vibration time and energy. Remove the coupon from the welding setup and write its identification number on both ends with a paint marker.</li>
		<li>Export the welding data (power and displacement of the sonotrode) to a spreadsheet and plot the power and displacement versus time curves during the vibration phase of the process. 
		Note: The displacement curve should plot the downward displacement of the sonotrode relative to its position at the onset of the vibration phase.</li>
		<li>Identify the displacement in the middle of the power plateau (stage 4) as shown on Figure 2 (in this case, 0.10 mm). 
		Note: This particular displacement value is the optimum travel that controls the duration of the vibration phase and will be used in every subsequent weld for the same welding force and amplitude.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 2" src="/files/ftp_upload/53592/53592fig2.jpg" /> 
Figure 2. Power (black) and displacement (grey) curves for the ultrasonic welding process indicating optimum travel value. The vibration phase of the ultrasonic welding can be divided in 5 stages. Optimum travel value is located within stage 4. Study case: carbon fiber reinforced polyetherimide -PEI substrates, 0.25 mm-thick flat PEI energy director, 300 N welding force, 86.2 &#181;m vibration amplitude, 0.25 mm travel. (Reprinted from reference 4 with permission from Elsevier.) <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="6">
	<li>Weld coupons at the optimum travel value for the given welding force and amplitude combination.
	<ol>
		<li>Repeat steps 2.1 to 2.5.6 for each weld. In step 2.5.3, use the optimum travel determined in step 2.5.8 for the corresponding welding force and amplitude combination. 
		Note: All LSS tests are carried out following ASTM D 1002 on a universal testing machine with a crosshead speed of 1.3 mm/min.</li>
	</ol>
	</li>
</ol>
3. Single Lap Shear Strength (LSS) Testing of Welded Coupons
<ol>
	<li>Measure and take note of the width of the overlap for each welded coupon.</li>
	<li>Turn on the universal testing machine and open the testing procedure for LSS on the computer.</li>
	<li>In the testing interface, enter the sample number and dimensions of the overlap. Set the force to 0 and the grip-to-grip separation to its initial position (for example, 60 mm).</li>
	<li>Position the sample in the grips of the testing machine as shown on Figure 3.</li>
</ol>
<img alt="Figure 3" src="/files/ftp_upload/53592/53592fig3.jpg" /> 
Figure 3. Schematic view of the clamping in the Zwick/Roell 250 kN universal testing machine (not to scale). The offset displacement between the top and lower grips allows aligning the load direction with the center weld line to minimize bending during the lap shear strength test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="5">
	<li>Start the testing procedure from the computer by clicking the &#34;Start&#34; button.</li>
	<li>After the sample breaks, remove it from the grips and secure both parts together with tape.</li>
	<li>Repeat steps 3.3 to 3.6 for all other samples.</li>
	<li>When the tests are completed, export the data to a spreadsheet and calculate the average LSS value, according to the procedure described in the standard, for each welding force and amplitude combination.</li>
</ol>

<ol><li>Yousefpour, A., Hojjati, M., Immarigeon, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fusion+bonding%2Fwelding+of+thermoplastic+composites%5BTitle%5D)+AND+%22J+Thermoplast+Compos%22%5BJournal%5D)">Fusion bonding/welding of thermoplastic composites.</a> J Thermoplast Compos. 17, 303-341 (2004).</li>
<li>Villegas, I. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((In+situ+monitoring+of+ultrasonic+welding+of+thermoplastic+composites+through+power+and+displacement+data%5BTitle%5D)+AND+%22J+Thermoplast+Compos%22%5BJournal%5D)">In situ monitoring of ultrasonic welding of thermoplastic composites through power and displacement data.</a> J Thermoplast Compos. 28 (1), 66-85 (2015).</li>
<li>Benatar, A., Gutowski, T. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrasonic+welding+of+PEEK+Graphite+APC-2+composites%5BTitle%5D)+AND+%22Polym+Eng+Sci%22%5BJournal%5D)">Ultrasonic welding of PEEK Graphite APC-2 composites.</a> Polym Eng Sci. 29 (23), 1705-1721 (1989).</li>
<li>Villegas, I. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Strength+development+versus+process+data+in+ultrasonic+welding+of+thermoplastic+composites+with+flat+energy+directors+and+its+application+to+the+definition+of+optimum+processing+parameters%5BTitle%5D)+AND+%22Compos+Part+A-Appl+S%22%5BJournal%5D)">Strength development versus process data in ultrasonic welding of thermoplastic composites with flat energy directors and its application to the definition of optimum processing parameters.</a> Compos Part A-Appl S. 65, 27-37 (2014).</li>
<li>Lu, H. M., Benatar, A., He, F. G. Sequential ultrasonic welding of PEEK/graphite composite plates. Proceedings of the ANTEC'91 Conference. , 2523-2526 (1991).</li>
<li>Potente, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrasonic+welding+-+principles+%26+theory%5BTitle%5D)+AND+%22Mater+Design%22%5BJournal%5D)">Ultrasonic welding - principles & theory.</a> Mater Design. 5, 228-234 (1984).</li>
<li>Stavrov, D., Bersee, H. E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Resistance+welding+of+thermoplastic+composites+-+an+overview%5BTitle%5D)+AND+%22Compos+Part+A-Appl+S%22%5BJournal%5D)">Resistance welding of thermoplastic composites - an overview.</a> Compos Part A-Appl S. 36, 39-54 (2005).</li>
<li>Villegas, I. F., Valle-Grande, B., Bersee, H. E. N., Benedictus, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+comparative+evaluation+between+flat+and+traditional+energy+directors+for+ultrasonic+welding+of+CF%2FPPS+thermoplastic+composites%5BTitle%5D)+AND+%22Compos+Interface%22%5BJournal%5D)">A comparative evaluation between flat and traditional energy directors for ultrasonic welding of CF/PPS thermoplastic composites.</a> Compos Interface. , (2015).</li>
<li>Levy, A., Le Corre, S., Villegas, I. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Modelling+the+heating+phenomena+in+ultrasonic+welding+of+thermoplastic+composites+with+flat+energy+directors%5BTitle%5D)+AND+%22J+Mater+Process+Tech%22%5BJournal%5D)">Modelling the heating phenomena in ultrasonic welding of thermoplastic composites with flat energy directors.</a> J Mater Process Tech. , 1361-1371 (2014).</li>
<li>Shi, H., Villegas, I. F., Bersee, H. E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Strength+and+failure+modes+in+resistance+welded+thermoplastic+composite+joints%3A+effect+of+fibre-matrix+adhesion+and+fibre+orientation%5BTitle%5D)+AND+%22Compos+Part+A-Appl+S%22%5BJournal%5D)">Strength and failure modes in resistance welded thermoplastic composite joints: effect of fibre-matrix adhesion and fibre orientation.</a> Compos Part A-Appl S. 55, 1-10 (2013).</li>
<li>Villegas, I. F., Bersee, H. E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrasonic+welding+of+advanced+thermoplastic+composites.+An+investigation+on+energy-directing+surfaces%5BTitle%5D)+AND+%22Adv+Polym+Tech%22%5BJournal%5D)">Ultrasonic welding of advanced thermoplastic composites. An investigation on energy-directing surfaces.</a> Adv Polym Tech. 29 (2), 113-121 (2010).</li>
<li>Harras, B. K., Cole, C., Vu-Khanh, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Optimization+of+the+ultrasonic+welding+of+PEEK-carbon+composites%5BTitle%5D)+AND+%22J+Reinf+Plast+Comp%22%5BJournal%5D)">Optimization of the ultrasonic welding of PEEK-carbon composites.</a> J Reinf Plast Comp. 15 (2), 174-182 (1996).</li>
</ol>

The authors declare that they have no competing financial interest.

The results presented in the previous section indicate the appropriateness of the straightforward method proposed in this paper for ultrasonic welding of thermoplastic composite single lap coupons for the purpose of mechanical testing. The following paragraphs discuss how the results validate the three main pillars of the method, i.e., use of flat loose energy directors, use of process feedback to define optimum duration of the vibration and use of displacement control, as well as the applicability and limitations of the technique.
With regards to the first pillar, flat energy directors are shown to allow successful welding of the TPC coupons. In ultrasonic welding of unreinforced plastics, energy directors in the form of resin protrusions with a smaller cross-sectional area than that of the joining overlap are required to generate higher cyclic strains and hence, preferential viscoelastic heat generation at the welding interface6. However, in ultrasonic welding of TPCs, flat energy directors with the same cross-sectional area as the welding overlap do successfully result in preferential viscoelastic heating at the welding interface owing to the lower compressive stiffness of the flat energy director and thus higher cyclic strains during the welding process. The heat generated at the interface melts the energy director and is transferred to the substrates. Under the effect of the welding force, the molten energy director is squeezed out of the welding overlap until the prescribed travel is reached. Optimum travel values result in fully welded overlaps and cross sections that resemble a thicker laminate since the thickness of the weld line is similar to that of the resin-rich areas in the substrates (see Figure 5). It should be noted that, when using flat energy directors, optimization of the energy director is not needed in order to achieve fully welded overlaps8, as opposed to more traditional energy director solutions, in which the size, shape and spacing between energy directors need to be optimized to achieve full coverage of the intended welding area10,11. Likewise, as compared to solutions such as triangular energy directors traditionally used for ultrasonic welding of TPCs3, flat energy directors have been shown to result in similar weld strength values while not having a significant negative impact on other important output of the process such as maximum power, energy or welding time8.
With regards to the second pillar, for a certain combination of welding force and amplitude, it is possible to define optimum travel values, i.e., travel values that lead to maximum strength, based on the power and displacement curves provided by the ultrasonic welder. Essentially, the different events in the power and displacement curves during the vibration phase of the welding process can be related to the physical changes occurring in the energy director and the TPC substrates during heating2. Accordingly, and as shown in Figure 2, the vibration phase of the welding process can be divided into the following 5 stages2:
Stage 1, characterized by continuous increase of the dissipated power until a maximum is reached and small retraction of the sonotrode to accommodate the vibration. In stage 1 heating of the energy director without any observable physical changes at the welding interface occurs. Stage 2, characterized by power decrease and no significant displacement of the sonotrode. In stage 2 the flat energy director starts to locally melt as a hot-spot nucleation and growth process. Stage 3, characterized by power increase and downward displacement of the sonotrode. In stage 3 the complete energy director is molten and starts to flow under the effect of the welding force. Stage 4, characterized by a power plateau and downward displacement of the sonotrode. In stage 4 the matrix in the uppermost layers of the composite substrates starts to locally melt along with the squeeze flow of the energy director. Stage 5, characterized by declining power and downward displacement of the sonotrode. In stage 5 melting of the matrix in the substrates is predominant.
The highest weld strength occurs during stage 4 since melting of the matrix in the uppermost layers of the composite substrates enables diffusion of polymer chains across the welding interface and hence molecular entanglement between the two substrates. This molecular entanglement develops a strong connection which results in fiber tearing during single lap testing, as seen in Figure 5. Beyond this optimum stage, excessive melting of the matrix in the composite substrates results in significant fiber distortion at the welding interface, which is believed to cause a drop in the weld strength4. The results presented in Figure 6, which correspond to a specific combination of welding force and amplitude of vibration, support this discussion. It must be noted that different force/amplitude combination would result in different output from the welding process in terms of maximum power and energy consumed as well as duration of the vibration phase2. Nevertheless, the method for determining the optimum travel value is independent of the chosen force/amplitude combination4.
With regards to the third pillar, displacement-controlled welding resulted in relatively low scatter in the apparent lap shear strength of joints welded in the optimum conditions. This is believed to result from the fact that all the samples were consistently welded in the same stage (i.e., stage 4) within the vibration phase of the process) as shown in Figure 4. Figure 7 indicates that if time had been used as the controlling parameter for the welding process, a higher scatter in the strength values could have been expected due to the significant overlapping in the vibration times for different travel values. According to Figure 8 and to results presented in literature12, energy is a better option than time as the controlling parameter. However, the welding energy is highly dependent on thickness of the substrates and nature of the welding jig and therefore the optimum energy value changes significantly when any of those two variables change4. Contrarily, displacement of the sonotrode is directly related to the squeeze flow of the energy director and matrix at the welding interface and thus can be expected to be less sensitive to changes in any of the above-mentioned variables4.
The novel method described in this paper allows straightforward near-field ultrasonic welding of thermoplastic composite coupons for single lap shear testing. The results presented refer to welding of CF/PEI composites but the same method has been successfully applied to other reinforced thermoplastic composites such as CF/polyphenyplene sulfide (PPS)8. As described in the paper, the method is directly applicable to the welding of a very specific geometry, however, in the case a different welding geometry is considered, there are three critical points that need to be taken into account. Firstly, increasing of the contact area between the parts to be welded has a direct impact on the maximum power dissipated during the welding process. Consequently, the maximum area that can be welded in one shot is limited by the maximum power delivered by the ultrasonic welder. Secondly, the method described in this paper considers unrestricted flow of the molten energy director out of the four edges of the welding overlap. A different welding configuration might, however restrict the polymer flow. This can be expected to have an impact on the evolution of the displacement of the sonotrode during the welding process and to probably impose limitations to displacement-controlled welding. Thirdly, if the thickness of the parts is such that the distance from the sonotrode to the welding interface is higher than 6 mm, specific considerations of far-field ultrasonic welding should be accounted for. Nevertheless, the method presented in this paper can be considered as a basis for the development of ultrasonic welding procedures for the assembling of actual thermoplastic composite structures. The main novelties and advantages of this method are simplified processing due to the usage of loose flat energy directors and the usage of the data provided by the welder to quickly define the optimum duration of the vibration for different combinations of force and amplitude. As compared to current trial-and-error procedures, the definition of process parameters based on process data has the potential to offer significant savings in the effort and time needed to develop welding processes for specific applications.

Thermoplastic composites (TPC) have the ability to be welded, which contributes to their cost-effective manufacturing. Welding requires local heating under pressure to soften or melt the thermoplastic resin of the joining surfaces and to allow for intimate contact and subsequent inter-diffusion of thermoplastic polymer chains across the welding interface. Once molecular inter-diffusion is achieved, cooling down under pressure consolidates the welded joint. Several welding techniques are applicable to thermoplastic composites which differ mainly in the source of heat1, however, the main &#34;adhesion&#34; mechanism, i.e., molecular entanglement, remains unchanged. Ultrasonic welding offers very short welding times (in the order of a few seconds), easy automation and it is virtually independent of the type of reinforcement in the thermoplastic composite substrates. Moreover, it offers the possibility for in situ monitoring2,3, which can be used for in line quality assurance or for fast definition of processing windows4. Ultrasonic welding of thermoplastic composites is mostly a spot welding process, however successful welding of longer seams through sequential ultrasonic welding has been reported in literature5. As opposed to resistance or induction welding, ultrasonic welding has not been industrially applied for structural joints between thermoplastic composite parts so far. Nevertheless, significant effort is currently being devoted to further development of structural ultrasonic welding of thermoplastic composites for aircraft applications.
In ultrasonic welding, the parts to be joined are subjected to a combination of static force and high-frequency low-amplitude mechanical vibrations transverse to the welding interface, which results in heat generation through surface and viscoelastic heating. Preferential heating at the welding interface is promoted through the use of resin protrusions on the surfaces to be welded which undergo higher cyclic strain, and thus higher viscoelastic heating, than the substrates6. Force and vibration are exerted onto the parts to be welded through a sonotrode connected to a press and to an ultrasonic train consisting of piezo electric converter and booster. Depending on the distance between the point where the sonotrode contacts the part to be joined and the welding interface, a distinction can be made between near-field and far-field ultrasonic welding. Near-field welding (less than 6 mm between sonotrode and welding interface) is applicable to a wider range of materials whilst the applicability of far-field welding to a specific thermoplastic material is highly dependent on the ability of the material to conduct sound waves6.
The ultrasonic welding process can be divided into three main phases. Firstly, a force build-up phase, during which the sonotrode gradually increases the force on the parts to be welded until a certain trigger force is reached. No vibration is applied during this phase. Secondly, a vibration phase, which starts once the trigger force is reached. In this phase the sonotrode vibrates at the prescribed amplitude for a certain amount of time generating the heat needed for the welding process. Microprocessor controlled ultrasonic welders provide several options to control the duration of the vibration phase, among them time (i.e., direct control), displacement or energy (indirect control). The force applied during this phase, i.e., welding force, can be kept constant and equal to the trigger force or can be gradually varied during application of the vibration. Thirdly, a solidification phase, during which the welded parts are allowed to cool down under a certain solidification force for a certain amount of time. No vibration is applied during this last stage.
Welding force, vibration amplitude, vibration frequency and duration of the vibration phase (either directly or indirectly controlled through energy or displacement) are the welding parameters that control heat generation. Force, amplitude and duration are user-defined parameters, while frequency is fixed for each ultrasonic welder. Solidification force and solidification time, also welding parameters, do not intervene in the heating process but affect the consolidation and, together with the rest of parameters, the final quality of the welded joints.
This paper presents a novel straightforward method for near-field ultrasonic welding of individual TPC coupons in a single lap configuration for subsequent mechanical, single lap shear (LSS), testing following ASTM (American Society for Testing and Materials) D 1002 standard. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints7. The welding method described in this paper is based on three main pillars. Firstly, loose flat energy directors are used for preferential heat generation at the joining interface8,9 during the welding process. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum duration of the vibration phase for a specific force/amplitude combination 2,4. Thirdly, the duration of the vibration phase is indirectly controlled through the displacement of the sonotrode in order to ensure consistent quality of the welded joints4. This welding method offers the following main novelties and advantages with regards to state-of-the-art welding procedures for thermoplastic composites: (a) simplified sample preparation enabled by the use of loose flat energy directors instead of traditional moulded energy directors3, and (b) fast and cost-efficient definition of processing parameters based on in-situ process monitoring as opposed to common trial and error approaches. Although the method described in this paper is geared towards obtaining a very specific and simple welding geometry it can serve as a basis to define a procedure for the welding of actual parts. A main difference in that case results from constrained flow of the energy director as opposed to unrestricted flow at the four edges of the overlap in single lap coupons.

<table><tbody><tr><td>&lt;strong&gt;Material/Reagent&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Cetex carbon fiber / polyetherimide (CF/PEI) 5 harness satin prepreg</td><td>TenCate Advanced Composites (www.tencate.com)</td><td>Contact vendor</td><td>Material used in this study for the specimens.</td></tr><tr><td>PFQD solvent degreaser</td><td>PT Technologies Europe (now Socomore - www.socomore.com)</td><td>Contact vendor</td><td>Solvent degreaser for cleaning the specimens and energy directors.</td></tr><tr><td>Cotton cloths</td><td></td><td></td><td>For general cleaning purposes. No specific vendor was used.</td></tr><tr><td>0.25 mm PEI film</td><td>TenCate Advanced Composites (www.tencate.com)</td><td>Contact vendor</td><td>Thin film used as energy director.</td></tr><tr><td>Adhesive tape</td><td>Airtech Advanced Materials Group (www.airtechintl.com)</td><td>1&quot; x 72 yds MFG # 327402 Contact vendor for catalog number</td><td>Used to attach energy director to bottom sample for ultrasonic welding.</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>V&amp;ouml;tsch oven</td><td>V&amp;ouml;tsch Industrietechnik (www.voetsch-ovens.com)</td><td>VTU 60/60 - Contact vendor for specific catalog number</td><td>Oven used to dry PEI film (energy directors) and PEI specimens before welding.</td></tr><tr><td>Rinco Dynamic 3000 ultrasonic welder</td><td>Aeson BV (www.aeson.nl/en/)</td><td>Contact vendor</td><td>20 kHz ultrasonic welding machine used for the welding experiments. Several sonotrode sizes available. Contact vendor for details. ACUCapture software included.</td></tr><tr><td>Zwick/Roell universal testing machine</td><td>Zwick (www.zwick.com)</td><td>Z250 - Contact vendor for specific catalog number</td><td>Universal testing machine with maximum load of 250 kN used for single lap shear strength measurements.</td></tr></tbody></table>

ultrasonic welding of thermoplastic composite coupons for mechanical characterization of welded joints through single lap shear testing

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ultrasonic welding process described in this paper is based on three main pillars. Firstly, flat energy directors are used for preferential heat generation at the joining interface during the welding process. A flat energy director is a neat thermoplastic resin film that is placed between the parts to be joined prior to the welding process and heats up preferentially owing to its lower compressive stiffness relative to the composite substrates. Consequently, flat energy directors provide a simple solution that does not require molding of resin protrusions on the surfaces of the composite substrates, as opposed to ultrasonic welding of unreinforced plastics. Secondly, the process data provided by the ultrasonic welder is used to rapidly define the optimum welding parameters for any thermoplastic composite material combination. Thirdly, displacement control is used in the welding process to ensure consistent quality of the welded joints. According to this method, thermoplastic-composite flat coupons are individually welded in a single lap configuration. Mechanical testing of the welded coupons allows determining the apparent lap shear strength of the joints, which is one of the properties most commonly used to quantify the strength of thermoplastic composite welded joints.

Carbon fiber reinforced polyetherimide (CF/PEI) samples were welded following the method described in this paper. The samples were obtained from a composite laminate made out of five-harness satin fabric CF/PEI, with (0/90)3S stacking sequence and 1.92 mm nominal thickness. Samples were cut from this laminate so that the main apparent orientation of the fibers was parallel to their longest side. Flat PEI energy directors with 0.25 mm thickness were used. Both the composite samples and the energy directors were dried in an oven at 135 &#176;C for 6 and 1 hr, respectively, as indicated by the manufacturer. Using power and displacement curves obtained for 0.25 mm travel, an optimum travel value around 0.10 mm, i.e., 40% of the initial thickness of the energy director, was obtained for the CF/PEI samples welded under 300 N welding force and 86.2 &#181;m peak-to-peak vibration amplitude (see Figure 2). Samples welded under these welding parameters (300 N welding force, 86.2 &#181;m amplitude and 0.10 mm travel) and solidification force and time of 1,000 N and 4 sec, respectively, yielded 37.3&#177;1.6 MPa (average &#177; standard deviation of five samples) apparent lap shear strength. Power curves obtained for each one of these samples as well as a representative cross-section micrograph and fracture surface are shown in Figures 4 and 5, respectively.
<img alt="Figure 4" src="/files/ftp_upload/53592/53592fig4.jpg" /> 
Figure 4. Power curves for CF/PEI coupons welded under optimum travel. The power curves (shifted vertically for clarity) show consistent ending of the welding process at stage 4. Vertical lines indicate the onset of stage 3. Study case: CF/PEI substrates, 0.25 mm-thick flat PEI energy director, 300 N welding force, 86.2 &#181;m vibration amplitude, 0.10 mm travel. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5 Left" src="/files/ftp_upload/53592/53592fig5left.jpg" /> 
<img alt="Figure 5 Right" src="/files/ftp_upload/53592/53592fig5right.jpg" /> 
Figure 5. Typical cross-section micrograph (top) and fracture surface (bottom) for CF/PEI coupon welded under optimum travel. Welded joints resemble a thicker composite laminate with no visible differences between the weld line (indicated by arrow) and the substrates. After lap shear testing, fracture surfaces show significant fiber tearing. Study case: CF/PEI substrates, 0.25 mm-thick flat PEI energy director, 300 N welding force, 86.2 &#181;m vibration amplitude, 0.10 mm travel. (Reprinted from reference 4 with permission from Elsevier.) <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
In order to check the validity of the approach presented in this paper to determine the optimum travel for a certain force/amplitude combination, samples were welded at different travel values, below and above the optimum travel, and subsequently tested. The rest of the welding parameters used for the welding of these samples were, as in the previous case, 300 N welding force, 86.2 &#181;m amplitude, 1,000 N solidification force and 4 sec solidification time. Figure 6 shows the apparent lap shear strength as a function of the travel (represented as a percentage of the initial thickness of the energy director).
<img alt="Figure 6" src="/files/ftp_upload/53592/53592fig6.jpg" /> 
Figure 6. Apparent lap shear strength of CF/PEI coupons welded under different travel values. Travel is represented here relative to the thickness of the energy director. Study case: CF/PEI substrates, 0.25 mm-thick flat PEI energy director, 300 N welding force, 86.2 &#181;m vibration amplitude, variable travel. (Reprinted from reference 4 with permission from Elsevier.) <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Finally, displacement-controlled welding was compared to other possibilities offered by the ultrasonic welder such as time- or energy-controlled welding. With this purpose, the lap shear strength values depicted in Figure 4 were plotted as a function of the vibration time (Figure 7) and of the welding energy (Figure 8). Vibration time and energy values for all the samples welded in this study were provided by the ultrasonic welder as an output of the welding process.
<img alt="Figure 7" src="/files/ftp_upload/53592/53592fig7.jpg" /> 
Figure 7. Apparent lap shear strength of CF/PEI coupons versus vibration time. Obtained by using vibration times of samples used to plot Figure 6. Study case: CF/PEI substrates, 0.25 mm-thick flat PEI energy director, 300 N welding force, 86.2 &#181;m vibration amplitude, variable travel. (Adapted from reference 4 with permission from Elsevier.) <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/53592/53592fig8.jpg" /> 
Figure 8. Apparent lap shear strength of CF/PEI coupons versus welding energy. Obtained by using welding energy values of samples used to plot Figure 6. Study case: CF/PEI substrates, 0.25 mm-thick flat PEI energy director, 300 N welding force, 86.2 &#181;m vibration amplitude, variable travel. (Adapted from reference 4 with permission from Elsevier.) <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53592/53592fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing at JoVE.com

Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

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

This paper presents a novel straightforward method for ultrasonic welding of thermoplastic-composite coupons in optimum processing conditions. The ...

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11.6K Views.  Delft University of Technology. A straightforward procedure for ultrasonic welding of thermoplastic composite coupons for basic mechanical testing is described. Key characteristics of this ultrasonic welding process are the use of flat energy directors for simplified process preparation and the use of process data for the fast definition of optimum processing conditions.

Video: Ultrasonic Welding of Thermoplastic Composite Coupons for Mechanical Characterization of Welded Joints through Single Lap Shear Testing

Manufacturing of Three-dimensionally Microstructured Nanocomposites through Microfluidic Infiltration

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite in&#64257;ltration of 3D interconnected microfluidic networks. The manufacturing of the reinforced beams begins with the fabrication of microfluidic networks, which involves layer-by-layer deposition of fugitive ink filaments using a dispensing robot, filling the empty space between filaments using a low viscosity resin, curing the resin and finally removing the ink.&#160;Self-supported 3D structures with other geometries and many layers (e.g.&#160;a few hundreds layers) could be built using this method. The resulting tubular micro&#64258;uidic networks are then infiltrated with thermosetting nanocomposite suspensions containing nanofillers (e.g.&#160;single-walled carbon nanotubes), and subsequently cured. The infiltration is done by applying a pressure gradient between two ends of the empty network (either by applying a vacuum or vacuum-assisted microinjection). Prior to the infiltration, the nanocomposite suspensions are prepared by dispersing nanofillers into polymer matrices using ultrasonication and three-roll mixing methods. The nanocomposites (i.e.&#160;materials infiltrated) are then solidified under UV exposure/heat cure, resulting in a 3D-reinforced composite structure. The technique presented here enables the design of functional nanocomposite macroscopic products for microengineering applications such as actuators and sensors.

Three-dimensional (3D) microstructured composite beams are fabricated through the directed and localized infiltration of nanocomposites into 3D porous microfluidic networks. The flexibility of this manufacturing method enables the utilization of different thermosetting materials and nanofillers in order to achieve a variety of functional 3D reinforced nanocomposite macroscopic products.

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite ...

Chemistry

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 ...

Experiments on Ultrasonic Lubrication Using a Piezoelectrically-assisted Tribometer and Optical Profilometer

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at a frequency above the acoustic range (20 kHz). As a solid-state technology, ultrasonic lubrication can be used where conventional lubricants are unfeasible or undesirable. Further, ultrasonic lubrication allows for electrical modulation of the effective friction coefficient between two sliding surfaces. This property enables adaptive systems that modify their frictional state and associated dynamic response as the operating conditions change. Surface wear can also be reduced through ultrasonic lubrication. We developed a protocol to investigate the dependence of friction force reduction and wear reduction on the linear sliding velocity between ultrasonically lubricated surfaces. A pin-on-disc tribometer was built which differs from commercial units in that a piezoelectric stack is used to vibrate the pin at 22 kHz normal to the rotating disc surface. Friction and wear metrics including effective friction force, volume loss, and surface roughness are measured without and with ultrasonic vibrations at a constant pressure of 1 to 4 MPa and three different sliding velocities: 20.3, 40.6, and 87 mm/sec. An optical profilometer is utilized to characterize the wear surfaces. The effective friction force is reduced by 62% at 20.3 mm/sec. Consistently with existing theories for ultrasonic lubrication, the percent reduction in friction force diminishes with increasing speed, down to 29% friction force reduction at 87 mm/sec. Wear reduction remains essentially constant (49%) at the three speeds considered.

We present a protocol for using a piezoelectrically-assisted tribometer and optical profilometer to investigate the dependence of ultrasonic wear and friction reduction on linear velocity, contact pressure, and surface properties.

Friction and wear are detrimental to engineered systems. Ultrasonic lubrication is achieved when the interface between two sliding surfaces is vibrated at ...

Fabrication of the Thermoplastic Microfluidic Channels

In our lab, we have successfully isolated nucleic acids directly from microliter and submicroliter volumes of human blood, urine and stool using polymer/nanoparticle composite microscale lysis and solid phase extraction columns. The recovered samples are concentrated, small volume samples that are PCRable, without any additional cleanup. Here, we demonstrate how to fabricate thermoplastic microfluidic chips using hot embossing and heat sealing. Then, we demonstrate how to use in situ light directed surface grafting and polymerization through the sealed chip to form the composite solid phase columns. We demonstrate grafting and polymerization of a carbon nanotube/polymer composite column for bacterial cell lysis. We then show the lysis process followed by solid phase extraction of nucleic acids from the sample on chip using a silica/polymer composite column. The attached protocols contain detailed instructions on how to make both lysis and solid phase extraction columns.

Here we demonstrate how to fabricate thermoplastic microfluidic chips using hot embossing and heat sealing. Then we demonstrate how to use in situ light directed surface grafting and polymerization through the sealed chip to form the composite solid phase columns.

In our lab, we have successfully isolated nucleic acids directly from microliter and submicroliter volumes of human blood, urine and stool using ...

Biology

Ultrasonic Fatigue Testing in the Tension-Compression Mode

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on exposing the specimen to longitudinal vibrations on its resonance frequency close to 20 kHz. With use of this method, it is possible to significantly decrease the time required for the test, when compared to conventional testing devices usually working at frequencies under 200 Hz. It is also used to simulate loading of material during operation in high speed conditions, such as those experienced by components of jet engines or car turbo pumps. It is necessary to operate only in the high and ultra-high cycle region, due to the possibility of extremely high deformation rates, which can have a significant influence on the test results. Specimen shape and dimensions have to be carefully selected and calculated to fulfill the resonance condition of the ultrasonic system; thus, it is not possible to test the full components or specimens of arbitrary shape. Before each test, it is necessary to harmonize the specimen with the frequency of the ultrasonic system to compensate for deviations of the real shape from the ideal one. It is not possible to run a test until a total fracture of the specimen, since the test is automatically terminated after initiation and propagation of the crack to a certain length, when the stiffness of the system changes enough to shift the system out of the resonance frequency. This manuscript describes the process of evaluation of materials' fatigue properties at high-frequency ultrasonic fatigue loading with use of mechanical resonance at a frequency close to 20 kHz. The protocol includes a detailed description of all steps required for a correct test, including specimen design, stress calculation, harmonizing with the resonance frequency, performing the test, and final static fracture.

A protocol for ultrasonic fatigue testing in the high and ultra-high cycle region in axial tension-compression loading mode.

Ultrasonic fatigue testing is one of a few methods which allow investigating fatigue properties in the ultra-high cycle region. The method is based on ...

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 ...

Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel

Friction stir spot welding (FSSW), a derivative of friction stir welding (FSW), is a solid-state welding technique that was developed in 1991. An industry application was found in the automotive industry in 2003 for the aluminum alloy that was used in the rear doors of automobiles. Friction stir spot welding is mostly used in Al alloys to create lap joints. The benefits of friction stir spot welding include a nearly 80% melting temperature that lowers the thermal deformation welds without splashing compared to resistance spot welding. Friction stir spot welding includes 3 steps: plunging, stirring, and retraction. In the present study, other materials including high strength steel are also used in the friction stir welding method to create joints. DP780, whose traditional welding process involves the use of resistance spot welding, is one of several high strength steel materials used in the automotive industry. In this paper, DP780 was used for friction stir spot welding, and its microstructure and microhardness were measured. The microstructure data showed that there was a fusion zone with fine grain and a heat effect zone with island martensite. The microhardness results indicated that the center zone exhibited a greater degree of hardness compared with the base metal. All data indicated that the friction stir spot welding used in dual phase steel 780 can create a good lap joint. In the future, friction stir spot welding can be used in high-strength steel welding applied in industrial manufacturing processes.

Here, we present a friction stir spot welding (FSSW) protocol on dual phase 780 steel. A tool pin with high-speed rotation generates heat from friction to soften the material, and then, the pin plunges into 2 sheet joints to create the lap joint.

Friction stir spot welding (FSSW), a derivative of friction stir welding (FSW), is a solid-state welding technique that was developed in 1991. An industry ...

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, ...

Crack Monitoring in Resonance Fatigue Testing of Welded Specimens Using Digital Image Correlation

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It is intended as a practical and reproducible procedure to identify macroscopic cracks at an early stage and monitor crack propagation during fatigue tests. It consists of strain field measurements at the weld using DIC. Images are taken at fixed load cycle intervals. Cracks become visible in the computed strain field as elevated strains. This way, the whole width of a small-scale specimen can be monitored to detect where and when a crack initiates. Subsequently, it is possible to monitor the development of the crack length. Because the resulting images are saved, the results are verifiable and comparable. The procedure is limited to cracks initiating at the surface and is intended for fatigue tests under laboratory conditions. By visualizing the crack, the presented procedure allows direct observation of macrocracks from their formation until rupture of the specimen.

Digital image correlation is used in fatigue tests on a resonance testing machine to detect macroscopic cracks and monitor crack propagation in welded specimens. Cracks on the specimen surface become visible as increased strains.

A procedure using digital image correlation (DIC) to detect cracks on welded specimens during fatigue tests on resonance testing machines is presented. It ...

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 ...