Name: ultrasonic welding of thermoplastic composite coupons for mechanical characterization of welded joints through single lap shear testing
Uploaded: 2016-02-11T14:00:00
Description: 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

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 ...

<ol>
	<li>Yousefpour, A., Hojjati, M., Immarigeon, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fusion+bonding/welding+of+thermoplastic+composites.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+monitoring+of+ultrasonic+welding+of+thermoplastic+composites+through+power+and+displacement+data.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonic+welding+of+PEEK+Graphite+APC-2+composites.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&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.">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. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequential+ultrasonic+welding+of+PEEK/graphite+composite+plates.">Sequential ultrasonic welding of PEEK/graphite composite plates.</a> Proceedings of the ANTEC'91 Conference. , 2523-2526 (1991).</li><li>Potente, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonic+welding+-+principles+&amp;+theory.">Ultrasonic welding - principles &amp; 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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resistance+welding+of+thermoplastic+composites+-+an+overview.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparative+evaluation+between+flat+and+traditional+energy+directors+for+ultrasonic+welding+of+CF/PPS+thermoplastic+composites.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modelling+the+heating+phenomena+in+ultrasonic+welding+of+thermoplastic+composites+with+flat+energy+directors.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strength+and+failure+modes+in+resistance+welded+thermoplastic+composite+joints:+effect+of+fibre-matrix+adhesion+and+fibre+orientation.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasonic+welding+of+advanced+thermoplastic+composites.+An+investigation+on+energy-directing+surfaces.">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/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+the+ultrasonic+welding+of+PEEK-carbon+composites.">Optimization of the ultrasonic welding of PEEK-carbon composites.</a> J Reinf Plast Comp. 15 (2), 174-182 (1996).</li></ol>

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 limitatio...

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 border="0" cellpadding="0" cellspacing="0" width="1179">
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		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Material/Reagent</td>
			<td style="width:308px;"></td>
			<td style="width:199px;"></td>
			<td style="width:363px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">Cetex&#174; carbon fiber / polyetherimide (CF/PEI) 5 harness satin prepreg</td>
			<td style="width:308px;">TenCate Advanced Composites (www.tencate.com)</td>
			<td style="width:199px;">Contact vendor</td>
			<td style="width:363px;">Material used in this study for the specimens.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">PFQD solvent degreaser</td>
			<td style="width:308px;">PT Technologies Europe (now Socomore - www.socomore.com)</td>
			<td style="width:199px;">Contact vendor</td>
			<td style="width:363px;">Solvent degreaser for cleaning the specimens and energy directors.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">Cotton cloths</td>
			<td style="width:308px;">-</td>
			<td style="width:199px;">-</td>
			<td style="width:363px;">For general cleaning purposes. No specific vendor was used.</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:311px;">0.25 mm PEI film</td>
			<td style="width:308px;">TenCate Advanced Composites (www.tencate.com)</td>
			<td style="width:199px;">Contact vendor</td>
			<td style="width:363px;">Thin film used as energy director.</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:311px;">Adhesive tape</td>
			<td style="width:308px;">Airtech Advanced Materials Group (www.airtechintl.com)</td>
			<td style="width:199px;">1&#34; x 72 yds MFG # 327402 Contact vendor for catalog number</td>
			<td style="width:363px;">Used to attach energy director to bottom sample for ultrasonic welding.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Name</td>
			<td style="width:308px;">Company</td>
			<td style="width:199px;">Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:311px;">Equipment</td>
			<td style="width:308px;"></td>
			<td style="width:199px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">V&#246;tsch oven</td>
			<td style="width:308px;">V&#246;tsch Industrietechnik (www.voetsch-ovens.com)</td>
			<td style="width:199px;">VTU 60/60 - Contact vendor for specific catalog number</td>
			<td style="width:363px;">Oven used to dry PEI film (energy directors) and PEI specimens before welding.</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:311px;">Rinco Dynamic 3000 ultrasonic welder</td>
			<td style="width:308px;">Aeson BV (www.aeson.nl/en/)</td>
			<td style="width:199px;">Contact vendor</td>
			<td style="width:363px;">20 kHz ultrasonic welding machine used for the welding experiments. Several sonotrode sizes available. Contact vendor for details. ACUCapture software included.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:311px;">Zwick/Roell universal testing machine</td>
			<td style="width:308px;">Zwick (www.zwick.com)</td>
			<td style="width:199px;">Z250 - Contact vendor for specific catalog number</td>
			<td style="width:363px;">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 samp...

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 ...

The overall goal of this procedure is to produce thermoplastic composite joints for basic mechanical testing using simplified energy directors, rapidly defined optimal welding parameters, and displacement control for consistent weld quality. This method helps answer key questions in the area of joining of composites such as what is the strength that can be expected from a welded joint and from a plastic composite. The main advantage of this technique is that it produces consistent high-quality welded coupons after fast definition of optimum welding parameters.For this procedure, have a microprocessor controlled ultrasonic welder that can operate at a constant amplitude. The welder must output process data such as dissipated power and displacement of the sonotrode versus time to a computer. This demonstration uses a custom-built jig designed to accurately position and clamp single-lap sheer samples.Turn on the ultrasonic welder and log into the computer. Before each experiment, log the following parameters:room temperature and humidity, the welding setup reference, the sonotrode type, the sample number and material, the width and thickness of the top and bottom samples, and the thickness of the energy director. Start the data acquisition software and open a new session.This demonstration uses a 40-millimeter diameter cylindrical sonotrode. The next steps are to add the samples and the energy director. First, clean the samples and the energy director.Then, tape the flat energy director to the bottom sample. It should cover an area slightly larger than the area to be welded. Then, place and align the bottom sample into the jig.And, clamp it down by tightening the top screw. Next, secure the other end of the energy director to the base of the setup using tape. Then, place the upper sample into the clamp, and align it.Now, tighten the top screw. Then, position the clamp for the top sample into the sliding platform and tighten both screws. Before proceeding with the weld, tighten all four screws once more.To achieve the highest weld strength, you have to determine the optimum duration of the vibration phase based on the displacement of the sonotrode. This duration must be determined for each combination of welding force and vibration amplitude. Begin by setting the control mode of the ultrasonic welder to the differential displacement.Next, input the welding force and the vibration amplitude. Please note that in this machine's setting, the amplitude is expressed as half the peak-to-peak amplitude value. Now, input the sonotrode's displacement or travel at the end of the vibration phase.Use a value equal to the initial thickness of the energy director, which in this case is zero point two five millimeters. Then, input the solidification force and the solidification time. In this example, these values are 1, 000 Newton and 4, 000 milliseconds.After inputting these settings, the system is ready to make ultrasonic welds. Put on protective eyewear, soundproof headphones, and start the process. After completing a weld, take note of the following output parameters:vibration energy, maximum power, and welding distance.Then, remove the coupon from the welding setup, and label it on both ends with an identification number, using a paint marker. Now, export the welding data to a spreadsheet, and plot the power and displacement versus time during the vibration phase of the process. Please note that this curve plots the downward displacement of the sonotrode relative to its position at the onset of the vibration phase.From the curves, identify the displacement in the middle of the power plateau. This displacement value is the optimum travel that controls the duration of the vibration phase for high-strength welds. Use this optimum travel value in every subsequent weld for the same welding force and amplitude.After completing all the welds, test their single lap sheer strength by following the ASTM D1002 Test Standard or a similar standard, and use a universal testing machine. Composite samples made out of carbon fiber reinforced polyetherimide with a nominal thickness of one point nine two millimeters were welded using the described method. Flat polyetherimide energy directors with zero point two five millimeter thickness were used.The optimum travel value for a 300 Newton welding force and 86.2 microns peak-to-peak amplitude was calculated as 40%of the initial thickness of the energy director. To validate the calculated optimum travel, samples were welded at different travel values and subsequently tested. Five welds were made for each value.The apparent lap sheer strength peaked at 40%of the initial thickness of the energy director, which was, indeed, the calculated optimum travel value. Fracture surfaces of the tested samples showed complete welded areas, which demonstrates the flat energy director's ability to weld the intended welding area. Finally, displacement controlled welding resulted in highly consistent weld quality, as shown by the low dispersion in strength value.A different strategy, such as time-controlled welding is expected to result in high scatter, as suggested by the significant overlapping of vibration times for different travel values, and, hence, different strength levels. After watching this video, you should know how to make ultrasonic welded joints in thermoplastic composites with optimum quality. This method is intended for basic mechanical testing, with simplified energy directors and simplified process parameter definition.Once mastered, the definition of optimum welding parameters and the welding of a batch of samples can be done in less than two hours if performed properly. Following this procedure, other methods, such as cross-section microscopy can be performed in order to answer additional questions, like thickness of the weld line, or, extension of heat affected zones.

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