## 5 Conclusions
results obtained were almost equal to those of the ZT-CFRP samples molded with OOA-VBO and cured under a full vacuum (about 0.82 bar) applied inside a vacuum bag and under the same compaction pressure as that applied on the stack of prepregs. The former had an improvement of about 11.34% in the ILSS, which was only 1.46% less than the improvement of the latter, compared with the ILSS of the control case (i.e., the traditional CFRP molded through the OOA-VBO method). Furthermore, both the macroscopic failure-mode analysis and the microscopic morphology indicated that the CNF z-threads prevented the ZT-CFRP samples from undergoing the typical shear delamination encountered by traditional CFRP samples, regardless of whether they are printed or molded; instead, the ZT-CFRP samples failed due to fiber-tension failure before any shear delamination could occur. As the OOA-VBO process has the flow-distribution medium to remove excessive resin, it manufactured ZT-CFRP samples with slightly higher carbon-fiber-volume fractions than the ZT-CFRP samples printed by the MCFA-AM method; hence, the higher carbon-fiber volume proportionally increased the ILSS values of the ZT-CFRP samples, which were dominated by the fiber-tension failure mode. On the other hand, despite the slight differences in carbon-fiber-volume fraction between the traditional CFRP samples manufactured by the OOA-VBO molding process and those manufactured by the robotic MCFA-AM 3D-printing process, the traditional CFRP samples had almost the same ILSS mean values; this was due to the fact that the interlaminar- and intralaminar-shear failures, which typically occur in traditional CFRP laminates, are usually dominated by the resin's shear strength and void content, but not the carbon-fiber-volume fraction. Based on the measurements, fracture mechanism, morphology, and explanation, it is evident that the ILSS and shear-fracture performance of CFRPs can be significantly enhanced using CNF z-threads,. In future studies, a compaction pressure higher than 0.78 bar and the use of ZT-CFRP with a higher carbon-fiber-volume fraction or stronger carbon fibers could further enhance the ILSS values (evaluated by Short Beam Shear test method) of ZT-CFRP samples printed by MCFA-AM, beyond those that the current study was able to yield. The novel MCFA-AM 3D printing process, by using the magnetic compaction pressure of 0.78 bar, effectively reduced the void content to close to that of the OOA-VBO's void-control performance, and enhanced the laminate-production speed to 2.7 times that of the OOA-VBO molding process. The experimental results showed that by combining advanced nanomaterials technology, such as the ZT-CFRP, with the novel MCFA-AM free-form 3D-printing process, compared with traditional CFRPs manufactured by using the OOA-VBO molding process, it possible to achieve similar void contents, increase the ILSS by 11.34%, enhance the production speed by 2.7 times, generate cost savings in terms of molding tools and consumables, enjoy the convenience of 3D printing, and obtain composite laminate products for structural applications with repeatable and consistently high performance. This new approach could also provide a more sustainable and greener manufacturing approach due to its ability to save on consumables and materials usage and to build stronger composite parts. In the future, there is ample room for improvement in the robotic MCFA-AM printer's construction and control. The improved synchronization between the printing speed, dynamic magnetic compaction control, multi-stage curing control, automated prepreg filament feeder, automated anchor unit, and synchronized multiple printheads could allow the production of higher-quality laminates or functionally-graded composite structures. The current robotic MCFA-AM printer is still a prototype, and several accessory components and the control algorithm are yet to be incorporated into its design and construction.