# Assessment of Crash Performance of an Automotive Component Made through Additive Manufacturing
## 3 Methods
### Rating Test  
The subsystem test allowed the preliminary analysis of the performance of the box during a knee impact, but this was not sufficient to represent what occurs in an automobile accident. To obtain more realistic biomechanical parameters, a complete and more complex model must be used. The objective was to fall within the range established by the Euro NCAP; therefore, the behavior of the additive box was considered acceptable, since it had the same biomechanical score as the box currently in production. The specific test considered was the frontal impact against a deformable barrier, officially named by the Euro NCAP as the Mobile Progressive Deformable Barrier (MPDB) [20]. The test simulated a  
Figure 6: Results of subsystem test. collision between two cars of the same weight traveling at a speed of 50 km/h. The protocol prescribed the use in each front seat of a Hybrid III 50 th Percentile Male Dummy (which has a size and weight greater than 50% of the American population) [21; 22], and two child dummies placed in the restraint systems in the rear seats. Our goal was to evaluate the biomechanical parameters of the lower limbs. Consequently, only the dashboard body and a passenger-side dummy were used instead of a full-scale model. The sled test [23], a biomechanical test of a subsystem that reproduces the same stresses on the dummies as a full-scale impact [24], was then carried out. The impact phenomenon was reproduced by subjecting the constrained elements of the sled (floor, seat, and dashboard) to a rigid movement of translation in the opposite direction of the vehicle's advancement. In this way, the dummy, due to inertial effects, was subjected to forward acceleration relative to the elements of the passenger compartment, and was consequently subjected to a loading condition similar to that of a full-scale impact. The LS-DYNA card *BOUNDARY_PRESCRIBED_MOTION_RIGID [15] was used to impose motion. The realistic law of motion used was derived from MPDB [20] experimental tests carried out on the same vehicle. The total number of elements was nearly \(1.30\times 10^{6}\). The calculation times were significantly longer (nearly 6 h using 56 parallel processors) due to the complex geometry (Figure 7). The Euro NCAP standard required, in this case, the evaluation of four parameters: compression of the femur and of the tibia, and sliding of the knee and of the tibia (obtained using the combination of moments and forces measured by the tibia load cells, Mx, My, and Fz respectively). In our specific case, femur compression and knee sliding were evaluated. In Figure 8, four distinct areas are noted with regard to the left femur:  
* t < 50 ms: The impact has not yet occurred, and there is a purely traction load. The peak at 40 ms was due to the foot's interaction with the floor. As a result of the floor, which was simulated as rigid, there was an overestimation of the loads coming from the feet;
* 50 ms < t < 60 ms: The impact has occurred, and the load increases until it changes sign and provides compression;
* t = 60 ms: The femur sinks completely inside the box and reaches the maximum compression load;
* t > 60 ms: The load decreases due to the removal of the dashboard. Figure 7: FEM of dummy-dashboard system. These four areas were less noticeable for the right femur (Figure 9), because the impact between the right femur and the dashboard occurred 5 ms later than it did for the left femur, due to the geometric characteristics of the dashboard. We observed that between 55 and 65 ms, the load tended to grow, but would never switch to compression. This is because the acceleration began to decrease between 55 and 60 ms, meaning the stress on the dummy also decreased. At about 70 ms, the set speed curve assumed a horizontal slope, thus exhausting the inertial thrust action on the dummy. The right femur did not reach the maximum sinking during this time interval; consequently, the load did not switch to compression, but remained constant.