## 3 Experimental Results and Discussion  
### SEM Images of the Welding Joints  
The welding joint images of the front of the eight patterns (No. 1-No. 8) are shown in Figure 6. As can be seen in this figure, the welding joints look sound without incomplete weld seams or deviation of the welding profile in comparison to the designed horn profiles. The profile of the welding bead is similar to the profile of the horn head. In order to examine the quality of the welding joints, only No. 1 was considered in detail. Magnification images of the front side, backside, and cross-section were captured by SEM. The results can be seen in Figures 7-10. Figure 7 shows the images of the front side and the backside, where the center zone is the welding seam. Because the roller with its specific pattern rotated on the fabric, the front side of the ultrasonic welding joints was compressed, as indicated in Figure 7a. Meanwhile, the fabric slid on the flat surface of the horn, and thus, the backside of the ultrasonic welding joints was flat (Figure 7b). It is well known that a mechanical vibration of ultrasonic frequency, with specific amplitude and mechanical force, from the roller can create heat at the interface of two fabrics. The heat is increased rapidly in the case that either the force increases or the welding speed decreases. As a result, the fabrics at the interface melt and solidify quickly. In order to investigate the welding quality, SEM images were taken at the boundary between the welding area and the base metal (i.e., fabric fibers) of the welding joints, both of the front side (Figure 8) and of the backside (Figure 9). Figure 8a shows the entire welding joint of the one-line engraving taken from the front view. The boundary between the welding area and the base fabric is relatively clear. The fibers in the welding area are compressed lower than the fabric surface. Welding defects can be found in the welding zone, since the base fabric is not of a homogenous material. Some fabric fibers are totally melted, but others still exist (as incompletely melted). This can be explained by the fact  
Figure 8: Scanning electron microscopy (SEM) images of the ultrasonic welding joints taken from the front with magnification of (**a**) \(\times\)30, (**b**) \(\times\)200, and (**c**) \(\times\)500. Figure 10: SEM images of the ultrasonic welding joints taken at a cross-section with magnification of (**a**) \(\times\)100, (**b**) \(\times\)200, and (**c**) \(\times\)500. Figure 9: SEM images of the ultrasonic welding joints taken from the backside with magnification of (**a**) \(\times\)30, (**b**) \(\times\)200, and (**c**) \(\times\)500.  
that the thickness of the fabrics is not uniform, and heat is not generated equally over the welding area. Figure 8b,c presents the structure at the edge of the welding boundary, where half of it is the welding area and the other half is the base metal (i.e., PP nonwoven fabric). A smaller size illustrates the structure of the base metal fiber, while a larger size expresses the welding region. The shapes of the welded fibers are changed due to the compression force and the ultrasonic heat. However, the fibers are not broken or cracked, and remain as continuous media. As a result, these structures can support the creation of the high strength required for welding joints. Figure 9 exhibits the entire welding joint of the one-line engraving taken from the backside view. As implied in Figure 9a, the rectangular shape is formed by the ultrasonic welding after using one-line engraving pattern. However, the four diamond shapes are generated by the heat roller during the fabric formation process. The edges of the rectangular shape between the welding area and the base fabric are very blurry. This can be explained by the fact that the backside of the base fabric directly contacted the fixed ultrasonic horn instead of the roller pattern. Inside the welding zone, some fibers are melted, while others are not; however, the region of the melted fibers is larger.