*2.4. Ultrasonic Welding Procedure*

GF/PP adherends were welded in a single lap configuration with an overlap area of 25.4 mm × 12.7 mm. A Dynamic 3000 ultrasonic welder (Rinco Ultrasonics, Danbury, CT, USA) with a maximum power of 3000 W and a constant operating frequency of 20 kHz was used with a 40 mm diameter titanium sonotrode. The booster and sonotrode gains were 1:1.5 and 1:3.85, respectively. Both adherends were clamped with aluminum bars and M8 socket head screws on a baseplate, as shown in Figure 2a,b. A nanocomposite film was placed between the adherends to act as the energy director. Films containing 15 wt.%, 20 wt.%, and 25 wt.% MWCNT with a thickness of 0.50 mm were used. Even though thermo-electrical characterization was performed on three different thicknesses, the thickest films were selected for welding and disassembly because they led to the highest bond line thickness, as will be discussed in Section 4.1.1.

**Figure 2.** Schematic of ultrasonic welding fixture used in this study for GF/PP adherends and MWCNT/PP energy director films: (**a**) side view and (**b**) top view. Dimensions are not to scale.

For all welds, during the vibration phase, a force of 1000 N and an amplitude of 38.1 µm were applied. The duration of the vibration phase was controlled through the vertical displacement of the sonotrode (also called "travel") until it reached a value equal to 60% of the initial films' thickness. After reaching the prescribed travel value, a consolidation force of 1000 N, for a duration of 4 s, was applied. Those welding parameters were chosen based on previous research [36,37]. The power and travel curves with respect to welding time were acquired for each weld.
