## 4 Validation with Automotive Production Equipment: Jig Structure
### Reconstruction of Impact Load  
The strains measured by the impact load transducer during 11 consecutive impacts under two loading velocities were examined. The time-domain strain signal recorded by the transducer is shown in Figure 7a. Figure 7b shows a sequence of the time-domain strain signals. The important parameters that characterize the measured strain induced by impact are the peak strain, impact duration, and strain in steady state, which is a strain induced by self-weight after impact. In the impact experiment with vehicle chassis, one  
Figure 6: Illustration of impact experiment in Hyundai Motors production line. (**a**) Jig structures and vehicle chassis; (**b**) jig structure installed with impact load transducer and strain gauges; (**c**) impact load transducer mounted on impact point; (**d,e**) strain gauges attached to the stress concentration region for validating FE simulation.  
or two successive peak compressive strain data were obtained because of oscillation. The vibration of a slim and flat vehicle chassis after the first impact causes oscillation of the strain data. The determination method is applied as follows. The peak strain is defined as the first compressive peak strain caused by the impact of the vehicle chassis. The impact duration is defined as the time difference between the two local minimum compressive strain points, which are the points nearest to the first peak compressive strain point. The strain in the steady state is defined by the average strain caused by the vehicle chassis weight after impact. The peak strain, impact duration, and strain in the steady state for the 11 consecutive impacts with two loading velocities are listed in Table 3. The average values of the peak strain, impact duration, and strain in the steady state with the loading velocity of 246.8 mm/s are \(-155.90\)\(\mu\varepsilon\), \(0.05630\) s, and \(-73.66\)\(\mu\varepsilon\), respectively, and their standard deviations are \(1.89\)\(\mu\varepsilon\), \(0.00148\) s, and \(3.39\)\(\mu\varepsilon\), respectively. Similarly, the average peak strain, impact duration, and strain in the steady state for the experiment with the loading velocity of 287.4 mm/s are \(-215.43\)\(\mu\varepsilon\), \(0.04288\) s, and \(-82.66\)\(\mu\varepsilon\), respectively, and their standard deviations are \(6.87\)\(\mu\varepsilon\), \(0.00222\) s, and \(1.51\)\(\mu\varepsilon\), respectively. Thus, the measured values of peak strain, impact duration, and strain in the steady state in each set of experiments are consistent enough to demonstrate the reliability of the impact load transducer.  
From the experimental results, we observe that the increased loading velocity results in an increased compressive strain of the impact load transducer, whereas the impact duration is shortened. In addition, there is a difference in strain in the steady state of 9 \(\mu\varepsilon\) between the two loading velocities.  
Figure 7: Results of impact experiments. (**a**) Time-domain strain signal measured by impact load transducer during 11 consecutive impacts; (**b**) a sequence of time-domain strain signal.  
Load curves were reconstructed from the average strain data (the peak compressive strain, impact duration, and strain in the steady state) using our method. The reconstructed impact loads for different loading velocities are shown in Figure 8. According to the reconstructed load curves, the peak load, impact duration, and load in the steady state at the two loading velocities are \(1083.90\) N/\(0.05630\) s/\(522.95\) N and \(1489.95\) N/\(0.04288\) s/\(584.33\) N, respectively. The reconstructed impact loads were employed as external forces in the numerical simulations.