JEC COMPOSITES MAGAZINE - Issue #77 - December 2012 - 47

are limits on the process window, as the strength of this cycle is lower than the others. Apparently, the combination of only two layers of PPS with a consolidation pressure of 0.7 MPa leaves insufficient PPS in the bond to achieve a high strength. The fracture surfaces of some specimens were examined with scanning electron microscopy to try to determine a reason for the difference in failure strength and scatter between both welding processes. Figure 6 shows a few examples where the main difference can be clearly distinguished. For the one-sided welding process (Figure 6 (a)), cavities of various sizes such as those illustrated were always present on the surface, but they were not evenly distributed over the entire surface, possibly causing the larger scatter on the results. Such cavities were never found in the two-sided welding procedure, the entire fracture surfaces being similar to the images shown in Figure 6(b).

be allowed. Two-sided welding showed very reproducible results, both within a single welding cycle and when comparing different welding cycles. Furthermore, there seems to be little influence, within certain boundaries, of the amount of PPS added and the consolidation pressure, yielding a wider process window. The latter is interesting, of course, if this technique is to be implemented in a production environment. Infrared welding can be used to form joints between large and complex parts and can be made fully automated, resulting in fast and economical production runs. High reproducibility and quality of the welded bonds can be obtained at high welding temperatures that can be reached with infrared emitters, allowing welding of virtually all thermoplastic materials. n
More information: www.composites.ugent.be Contact: Klaas.Allaer@UGent.be Acknowledgements The authors are highly indebted to the Fund of Scientific Research – Flanders (F.W.O.) for sponsoring this research and to Ten Cate Advanced Composites for supplying the material. References [1] Yousefpour A., Hojjati M., Immarigeon J.P. Fusion bonding/welding of thermoplastic composites. Journal of Thermoplastic Composite Materials, 17 (4): pp 303-341 (2004). [2] Ten Cate – Aerospace Composites. http://www.tencate.com [3] De Baere I., Van Paepegem W. and Degrieck J. Feasibility study of fusion bonding for carbon fabric reinforced polyphenylene sulphide by hot-tool welding. Journal of Thermoplastic Composite Materials, 25 (2): pp 135-151 (2012). [4] Szekrenyes, A. Improved analysis of unidirectional composite delamination specimens. Mechanics of Materials, 39 (10), pp 953-974 (2007). [5] Mathews, Mary J. and Swanson, Stephen R. Characterization of the interlaminar fracture toughness of a laminated carbon/epoxy composite. Composites Science and Technology, 67 (7-8), pp 1489-1498 (2007). [6] De Baere I., Allaer K., Jacques S., Van Paepegem W. and Degrieck J. Interlaminar behavior of infrared welded joints of carbon fabric-reinforced polyphenylene sulfide. Polymer Composites, 33 (7): pp 1105-1113 (2012). [7] Brucato V., Piccarolo S., La Carrubba V. An experimental methodology to study polymer crystallization under processing conditions. The influence of high cooling rates. Chemical Engineering Science, 57: pp 4129-4143 (2002). [8] Liliana B. Nohara, Evandro L. Nohara, Mirabel C. Rezende. Study of cristallization behavior of poly(phenylene sulfide). Polymer Science and Technology, 16 (2) : pp 104-110 (2006).

b
Fig. 6: SEM observation of the fracture surfaces (a) One-sided welding, cavities present (b) Two-sided welding, no cavities present.

The research on infrared welded joints has already revealed interesting results, so the study on the properties of these bonds is being continued. The dynamic fatigue behaviour of infrared-welded joints is currently being investigated, as it plays an important role in reliability-based design of parts and structures.

Conclusions
Infrared welding is a fast, economical and safe method for joining plastics. It can be easily automated and processing conditions can be easily monitored. Because it is a noncontact heating method, it can be used for continuous joining. It was found that although high failure loads are possible, the one-sided welding method yields very irreproducible results, not only between separate welding cycles with the same settings, but also between the three specimens coming from one cycle, which of course cannot

No77 December 2012 /

jec composites magazine 47

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JEC COMPOSITES MAGAZINE - Issue #77 - December 2012

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