*2.2. Drop Weight Test and Simulation*

2.2.1. Geometry Modeling, Mesh, and Weld Constraints for FE Simulation

An FE simulation for the drop weight test was performed using ABAQUS/explicit software. Figure 2 shows the geometry modeling and welding constraints between the HPF center pillar and PW. The fine mesh was defined in the impact region, and the rough mesh was defined in other regions to reduce computation time. The element types of the center pillar and weld nodes were S4 and CNN3D2, respectively. The PW was welded to the HPF center pillar with 1200 × <sup>440</sup> × 51.5 mm<sup>3</sup> dimension. As shown in Figure 2b, the master weld node was defined on the element of center pillar, and the slave weld node was defined on the element of the PW. The master and slave weld nodes were bonded, and the attachment method used for the welding connector was point to point. The damage criterion and damage evolution of weld constraints were not applied because a fracture did not occur at the weld point. The detailed weld conditions for the FE simulation are listed in Table 2.

**Figure 2.** Center pillar and PW: (**a**) geometry and mesh; (**b**) weld constraints.

**Table 2.** Spot weld conditions for FE simulation.


2.2.2. Boundary Conditions for Drop Weight Test

Figure 3 shows the simulation and experimental apparatus for the drop weight test. The center pillar was fixed by clamp, as shown in Figure 3a. The drop height from the center pillar was 610 mm, and the load cell was attached to an impactor with a weight of 160 kg. A drop weight simulation was also performed for comparison with the experimental data. The impactor velocity was 3.450 m/s before collision. The 6 degrees of freedom of the center pillar were fixed in the zig region by a clamp. The friction coefficient between the center pillar and impactor was 0.1. The collision time was 0.18 s. The detailed boundary conditions for the drop weight test are listed in Table 3.

**Figure 3.** Boundary conditions for the drop weight test: (**a**) experiment; (**b**) simulation.


