## 3 Results and Analysis  
### Short-Beam-Shear-Test Data and Sample Fracture Modes  
The amount of fiber in a fiber-reinforced composite directly corresponds to some of the mechanical properties of the composite. Theoretically, a higher fiber-volume fraction (_FVF_) yields almost linearly increased tensile and compressive strengths, but not necessarily increases in the ILSS of the composite. The ILSS is more dominated by the matrix, voids, and matrix-fiber interfacial bonding if no nanoparticle reinforcement is considered. From the perspective of controlling the _FVF_ of a FRP prepreg or laminate, the fiber-volume fraction can be calculated using Equation (2). \[FVF=\left(No.\ of\ pl\ \text{flies}\ of\ fabrics\ \times\ A_{\omega}\right)/ \left(\rho_{f}\ \times\ t_{lam}\right) \tag{2}\]  
where \(A_{w}\) = the areal weight of a ply of fabric in g/cm\({}^{2}\), \(t_{lam}\) = the thickness of the laminate in cm, and \(\rho_{f}\) = the density of the fiber in g/cm\({}^{3}\). Each layer of the prepreg's thickness can be determined as \(t_{lam}/No.\ of\ pl\ \text{flies}\ of\ fabrics\). The carbon fabric's areal weight and carbon-fiber density were provided by the manufacturer, and they were 0.019 g/cm\({}^{2}\) and 1.79 g/cm\({}^{3}\), respectively. Furthermore, the _FVF_ of a single prepreg used in the MCFA-AM method was maintained in such a way that they all retained 53% _FVF_. To achieve this, a gage-controlled conduit was used to slide the fully impregnated prepregs through to remove the excessive resin and control the final prepreg thickness. The sample sizes were kept the same for all the laminate types, with a specimen thickness of 2.5 mm, a specimen width of 5.0 mm, and a specimen length of 15.00 mm. The measurement error was \(\pm\)3% for the individual samples. Figures 10 and 11 display the force vs. crosshead-position plots for all the different laminate types during the SBS test. The detailed data values, with the types of failure, are presented in Appendix A.  
Figure 10: Load vs. Crosshead position plots of (**a**) control CFRP/OOA-VBO, (**b**) ZT-CFRP/OOOA-VBO, (**c**) no-pressure 3D CFRP, (**d**) CFRP/MCFA-AM-laminate samples. Many curves can be observed on the plots, reaching peak values almost in a linear manner and then continuously dropping, with slight oscillations, before stopping. This type of curve trend can be explained as a process in which a thick, short beam was gradually delaminated into multiple thinner short beams. Some of the samples also monotonically reduced in strength after the initial failure. A few of the curves had a sudden drop to more than 30% of the loading drop-off value after peaking, possibly indicating different fracture modes, other than pure delamination, which would have caused the short beam to suddenly lose its mechanical function almost completely. For the ZT-CFRP/OOA-VBO samples, the CNF z-threads formed an interlocking network between carbon fibers and tended to intervene by preventing or redirecting the propagation of resin cracks, resulting in an almost consistent maximum loading until multiple small fractures ultimately led to complete fiber breakage. The MCFA-AM-printed ZT-CFRP/MCFA-AM sample's curves showed similar behavior, with slight fluctuations after reaching the maximum loading (Figure 11). The different failure modes for all the laminate types are shown in Figures 12 and 13. Figure 11: Load vs. crosshead position of ZT-CFRP/MCFA-AM-laminate samples. Figure 12: Failure modes of the SBS-tested samples. (**a**) Control CFRP/OOA-VBO sample: interlayer-shear-failure mode. (**b**) ZT-CFRP/OOA-VBO sample: tension-failure mode. (**c**) No-pressure 3D CFRP sample: mixed-interlayer-shear-failure mode and tension-failure mode. (**d**) CFRP/MCFA-AM sample: interlayer-shear-failure mode. Figure 13: The SBS test of a ZT-CFRP/MCFA-AM sample showed the fiber-tensile-failure mode on the lower half section of the laminate instead of the expected standard delamination-failure mode.