accelerometer system mounted on the left side of the beam (Fig. 37.4). The accelerometer data was obtained using a data acquisition system. Once the two trigger tapes touched each other (Figs. 37.1 and 37.2b) the data acquisition system (i.e. with a pre-trigger value) captured the accelerometer data. All data was filtered and sampled according to SAE J211 [10]. Histories of displacement and velocity were obtained from the accelerometer and video tracking data. Newton’s second law was employed to obtain total force-time history of the impactor-sled. Following completion of each test, the bumper and crush-cans were photographed to document any resulting damage. Additional close-up photographs of visible damage were also taken. 37.3 Results and Discussion A number of tests were conducted in order to optimize the impact speed. The basic principle for determining the speed was to minimize any bottoming-out force between the front beam (Fig. 37.1) and the bottom can of an FBCC structure (Fig. 37.2b). Several tests were performed (i.e. only five are presented here) based on the optimized speed. The speed of each test was measured based on the two distinct methods mentioned earlier. Figure 37.5 illustrates the velocity-time histories of the impactor-sled obtained from these two methods. Based on the results, excellent correlation exists between the two measurement approaches. The total mass of the impactor-sled was 708.43 lb (321.34 kg). The impactor-sled struck the lower part of an FBCC structure (Fig. 37.6) with an average speed of 20.31 mph (9.1 m/s). The impact speed for each test is given in Table 37.1. Accelerations in the y and z direction (i.e. off-axis accelerations) are compared to the axial deceleration (i.e. along the xdirection) in Fig. 37.7. These data were obtained from the triaxial accelerometer system mounted on the left side of the beam (Fig. 37.4). Similar deceleration profile was seen for all five tests. However, it should be noted that a secondary peak was not observed for FBCC #45. It is also evident that the z-acceleration was negligible, whereas the y-acceleration was relatively small when compared to the x-deceleration pulse. The y-acceleration was due to the lateral motion of the bumper beam as the bottom can was folding and bending. The average force-time history and average force-displacement curves for the five FBCC structures are shown in Fig. 37.8. All five tests were in excellent agreement with respect to each other. As mentioned before, FBCC #45 did not show a secondary peak. This was due to the fact that the bottom can did not completely crush. This is illustrated in Fig. 37.9. The area under force-time history and force-displacement curves were calculated for each test and the results are described in Table 37.1. The coefficient of variation in both impulse and the absorbed energy was very small indicating excellent repeatability. Based on Fig. 37.8 and Table 37.1, impact responses of FBCC samples closely match each other. 37.4 Conclusions This study has presented a novel component-level experimental investigation on impact response of generic steel FBCC structures subjected to a 30 front-angular impact. Excellent agreement was obtained for measuring the Impactor-sled speed based on high-speed camera and accelerometer data. The off-axis acceleration in the z-direction was negligible and the acceleration in the y-direction was due to the folding and bending of the bottom can. Crash pulse, force-time history, forcedisplacement and impact characteristics from various FBCC tests were all consistent. The energy absorbed in each test was within a tight band of 12.60–13.16 kJ with an average value of 12.78 kJ. The tests were repetitive and the variation in the results was insignificant. 252 A. Seyed Yaghoubi et al.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==