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 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 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">
	<tbody>
		<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 ...

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11.5K 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.