## 2 Materials and Methods
### Methods for Manufacturing and Testing Samples
#### 2.2.4 Mcrea-Am Process  
Both the CFRP and ZT-CFRP laminates were printed using an in-house-developed Mcrea-AM 3D-printing head prototype. Note this Mcrea-AM printing-head design can also work on thermoplastic CFRP tapes, in addition to the thermoset CFRP tapes used in this study. Figure 5 depicts a schematic of the novel Mcrea-AM printing head (i.e., printhead) proposed in the patent publication [9] and a block diagram showcasing the main components. A printhead designed based on the novel Mcrea-AM method was mounted on a six-degrees-of-freedom robotic arm (Motoman GP 7 Robot Arm form Yaskawa America, Inc., Waukegan, IL, USA), which was programed to move the Mcrea-AM printhead along a predetermined straight-line path (for this experiment, the Mcrea-AM printhead was operated at a constant height and the clamping anchor was adjusted after stacking each prepreg layer) to produce the straight/flat laminate samples. After making the prepregs, it took approximately 45 min to use the robotic Mcrea-AM-printer prototype to print the stack of prepregs onto a CFRP or ZT-CFRP laminate and perform post-cleaning. A magnetic compaction force of 13.72 N was measured against a pressing area of 17.56 mm\({}^{2}\), which yielded a compaction pressure of 0.78 bar (average), which in turn was utilized to compress and stack the prepregs at a printhead speed of 2.82 mm/s. The steps followed are described below:  
Figure 4: OOA-VBO layup scheme used for the preparation of laminates. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Time** & **Temperature (°C)** & **Vacuum-Pump Status** \\ \hline
20 min & 30 °C & On \\ \hline
1 h & 140 °C & On \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Curing cycle for OOA-VBO method. Step 1: one end of a ply of ZT-CFRP prepreg tape is anchored; the MCFA-AM print-head, with the magnetic field emitter switched on to a desired field strength to attract the backing article, smoothly driven from one end to the other by the robot arm, is used to position, compact, and cure (solidify) the ZT-CFRP-prepreg tape into a lamina in free space (air) (see Figure 6). 2. Step 2: reduce the magnetic field to release the backing article (it was collected by hand for this current underdevelopment prototype, but it will have an automatic collecting unit in the future, fully developed MCFA-AM printer); load a new layer of prepreg on top of the previous cured layer, and increase the magnetic field to a desired field strength to attract the backing article to clamp the new layer against the previously cured layer. 3. Step 3: the MCFA-AM printhead, with the magnetic field emitter switched on to a desired field strength to attract the backing article, smoothly driven from one end to the other by the robot arm, is then used to lay down, compact, and cure a new layer of ZT-CFRP-prepreg tape on top of the aforementioned cured ZT-CFRP layer. 4. Step 4: repeat Step (2) and Step (3) until the desired layers of CFRP prepreg are compacted and cured into a CFRP-laminate part. 5. Step 5: reduce the magnetic field and release the backing article; detach the cured/solidified ZT-CFRP laminate part from the anchoring fixture. A 250-watt (120 V) heat lamp was used to induce the desired curing temperature, 140 \({}^{\circ}\)C on the fast-curing ZT-CFRP prepreg tape, and it was set in place pointing to the compaction spot, where the magnetic compaction force was exerted on the prepreg. Similar to the OOA-VBO cured samples, before the ILSS tests were performed on the samples, all the laminates were further subjected to 4 h of post-curing to ensure full curing of the resin and to yield a fair experimental comparison among all samples. Figure 6 shows the robot-arm-driven MCFA-AM printer (under development), to which a tape-like feedstock or filament (e.g., CFRP prepreg or ZT-CFRP prepreg) was clamped/anchored on one end, while the other end was fed by hand, and the tape was held in place and compressed by a backing article (metallic rod) attracted by a magnetic field emitter (sheathed with aluminum foil).