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Ultrasonic welding of thermoplastic composites has become an important process in industry because of its relatively low cost and resultant high quality joints. An experimental study, based on the Taguchi orthogonal array design, is reported on the effect of different processing factors on the joint strength of ultrasonically welded composites, including weld time, weld pressure, amplitude of vibration, hold time, hold pressure, and geometry of energy director. Three materials were used in the study: virgin polypropylene, and 1 0 9 4 0 and 30% glass-fiber filled polypropylene composites. Experiments were carried out on a 2000-Watt ultrasonic welding unit. After welding, the joint strength of the composites was determined by a tensile tester. For the factors selected in the main experiments, weld time, geometry of energy director and amplitude of vibration were found to be the principal factors affecting the joint properly of ultrasonically welded thermoplastic composites. Glassfiber fdled polymers required less energy for successful welding than the non-filled polymer. The joint strength of welded parts increased with the fiber content in the composites. In addition, a triangular energy director was found to weld parts of the highest strength for virgin polypropylene and 10% glass-fiber filled polypropylene composites, while a semi-circular energy director was found to weld the highest strength parts for 30% glass-fiber filled composites.T o whom correspondence should be addressed energy director, which has the smallest cross section and therefore the highest strain, heats, melts, and flows to fill the interface with molten polymer and to fusion bond the parts (3).Up to the present, some research work has been done in the ultrasonic welding of thermoplastics. Benatar et d. (4, 5) completed research in both near-field and far-field welding of different thermoplastics, including polystyrene, ABS, polyethylene and polypropylene. They proposed a lumped parameter model to predict the heating rates and energy dissipation of the ultrasonic welding. Michaeli and Korte (61 used a statistic regression method to analyze experimentally the welding process of thermoplastics. Gerdes et al. (7) completed a finite element analysis of plastic part failure during ultrasonic welding. He and Benatar (8) studied the effects of amplitude and pressure control 132

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Ultrasonic welding of thermoplastic composites has become an important process in industry because of its relatively low cost and high quality resultant joints. However, the optimization of this technique has been essentially based on a trial-and-error process. In this report, an L18 orthogonal array design based on the Taguchi method was conducted to optimize the joint strength of ultrasonically welded thermoplastic composites. The materials used were 15 and 35% glass-fiber filled nylon-6 composites. Specimens for ultrasonic welding were welded on a 2000-watt welder and their joint strengths were determined by a tensile tester. The experimental result suggests that the amplitude of vibration, hold time and geometry of the energy directorsare the principal factorsaffecting the joint property of ultrasonically welded nylon composites. Semicircular energy directors were found to weld products of the highest strength. In addition, the joint strength of the parts increases with the fiber content in the composites, but decreases with the moisture of the materials.

To achieve dramatic improvements in the performance of natural rubber (NR), the graphite oxide nanosheets (GON)-reinforced NR nanocomposites have been prepared through solution mixing on the basis of pretreatment of graphite. The mechanical and thermal properties of GON/NR nanocomposites were characterized in contrast to the carbon black (CB)/NR nanocomposite. The mechanical properties of the GON-reinforced NR showed a considerable increase compared to the neat NR and traditional CB/NR nanocomposite. The initial modulus of pure NR was increased for up to 53.6% when 7 wt% GON is incorporated. The modulus and strength of NR with GON appear to be superior to those of CB with the same filler content. The dispersion state of the nanofillers into NR was investigated by scanning electron microscopy and X-ray diffraction, and the results indicated that nanofillers have been dispersed homogeneously in the NR matrix. Fourier transform infrared spectra showed possible interfacial interactions between fillers and NR matrix. Differential scanning calorimetry and thermogravimetric analysis showed that the T g and thermal decomposition temperature of NR slightly increased with the addition of the fillers, especially for that of GON/NR nanocomposites. According to this study, application of the physical and mechanical properties of GON to NR can result in rubber products which have improved mechanical, physical, and thermal properties, compared with existing NR products reinforced with CB.