## 3 Results and Discussion
### Deep Drawing of the FML  
At RT, the drawing force of the FML under deep-drawing conditions decreased with the increasing die edge radius, and the slope of the force-displacement curve increased significantly with increasing core thickness. Basically, the higher slope refers to higher strengthening potential, as shown earlier through the uniaxial tensile test in Figure 1.  
Figure 13: Strain evolution along a cross-sectional line of: (**a**) MPM\({}^{02}\) with different core thicknesses at different drawing depths; (**b**) monolithic TS290; and (**c**) strain distribution of MPM\({}^{02}\)-PA1.0 at RT. However, the maximum drawing depth and the corresponding maximum drawing force decreased, as expected [41], as shown in Figure 14a. With a thicker core layer, the tensile stress applied to the outer steel sheet at the punch edge was greater, as was the cracking probability, as shown in the sample image. Adjusting the process parameters and the thickness ratio did not lead to a change in the maximum stroke of the FML, which was limited to less than 25 mm. Furthermore, the strain evolution of the FML differed from that of the monolithic steel sheet and the MPM in that the anisotropy of the core RG led to directional strain evolution along the warp and weft at the punch edge, as shown in Figure 14b. Because the fibres were less mobile in the warp and weft directions, the tensile stresses applied to the outer steel sheet in the 0\({}^{\circ}\) and 90\({}^{\circ}\) directions were greater in comparison to the 45\({}^{\circ}\) direction and, thus, more likely to cause cracks. The strain at the punch edge shifted to the \(\varepsilon_{2}=0\) direction after a transient evolution along the \(\varepsilon_{2}=0.5\varepsilon_{1}\) direction due to the stress concentration and necking of the cover steel sheet along the warp and weft directions of RG. Another difference is that the strain evolution in the flange area was also directional, with the strain evolution along the 45\({}^{\circ}\) direction being higher than that in the 0\({}^{\circ}\) and 90\({}^{\circ}\) directions, due to the fact that the core layer was prone to shear deformation in the 45\({}^{\circ}\) direction [28; 42]. Moreover, the strain evolution of the outer steel sheet of FML already exceeded its corresponding FLC level (solid red line in Figure 14b) at RT, indicating the cracking of the steel. The detailed strain evolution in each direction was analysed with the help of centreline cross-sections. Figure 15 shows the strain evolution of the FML for different material combinations. It can be observed that the final strain evolution in the flange area showed anisotropy for both isotropic (TS275) and anisotropic (TS290) cover sheets, with slightly higher strain values in the 45\({}^{\circ}\) direction. For the warm deep drawing of FML, at temperatures above the melting point of PA6 (220 \({}^{\circ}\)C), severe wrinkling on the inner cover sheet and an appearance of waviness on the outer side took place, as shown in Figure 16a. The reason for this was that the molten matrix in the core of the FML did not provide the cover with the ability to resist the circumferential compressive stress of the blank, as well as due to a larger gap size (3.3 mm) by \(r_{d}=15\) mm. A large gap-to-sheet thickness ratio often leads to waviness during the deep drawing of the sheet [43]. Thus, in subsequent tests, improvements in the deep-drawability of the FML can be achieved by increasing the holding force (100 kN); thickening the covers; reducing the die radius and gap size. This can be substantially improved by reducing the forming temperature to 200 \({}^{\circ}\)C. Figure 16b shows the results in terms of drawing force and depth. Figure 14: (**a**) Force–depth progress of FML02 with different core thicknesses and holding forces, and (**b**) strain evolution for two core thicknesses (0.5 and 1.0 mm). The increase in temperature allowed the FML to reach a stroke of 40 mm, and the punch was experimentally stopped at this displacement.