Second impact point

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The graphs in figure 5.95 are in accordance with the considerations made for the deceleration curve. On the plot that shows the contact force over the simulation, it is possible to observe that the trend of the black curve with the modified front frame is almost superimposed to the original one and the peak contact force is slightly higher than the original one, but the difference can be considered negligible. In this case, the requirement of the suggested upper limit of the contact force is satisfied while focusing on the green curve, it is possible to see that in the dashboard with the modified rear cover there are some points that are above the suggested limit, and this is due to higher stiffness of the aluminum alloy. As previously described, this condition is still acceptable in terms of virtual validation, but it is necessary to check if possible problems may

arise when physical tests are carried out.

Focusing instead on the plot that shows the contact forces as a function of the displacement, the green curve with the modified rear cover made of Al alloy, as expected, shows a more elastic behavior because, from the maximum displacement, the interface force decreases more rapidly with respect to the original case. This is caused by a higher release of energy from the dashboard to the head form after the impact phase and consequently less presence of plastic permanent deformations.

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Figure 5.99 – Full view and left side section of the head impact with modified front frame (time 10 ms)

Figure 5.98 – Full view and left side section of the head impact with modified front frame (time 15 ms)

Figure 5.100 – Full view and left side section of the head impact with modified front frame (time 20 ms)

Figure 5.101 – Full view and left side section of the head impact with modified rear cover (time 0 ms)

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Figure 5.102 – Full view and left side section of the head impact with modified rear cover (time 5 ms)

Figure 5.103 – Full view and left side section of the head impact with modified rear cover (time 10 ms)

Figure 5.104 – Full view and left side section of the head impact with modified rear cover (time 15 ms)

Figure 5.105 – Full view and left side section of the head impact with modified rear cover (time 20 ms)

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Finally, in figures 5.106, 5.107 and 5.108 it is shown a focus on the front frame of the monitor (yellow component) while in figures 5.109, 5.110 and 5.111 it is shown a focus on the rear cover (green component).

Figure 5.106 – Transparent bottom view of the monitor with only front frame visible in green at time 0 and 5 ms

Figure 5.107 – Transparent bottom view of the monitor with only front frame visible in green at time 10 and 15 ms

Figure 5.108 – Transparent bottom view of the monitor with only front frame visible in green at time 20 and 25 ms

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Figure 5.109 – Transparent bottom view of the monitor with only rear cover visible in green at time 0 and 5 ms

Figure 5.110 – Transparent bottom view of the monitor with only rear cover visible in green at time 10 and 15 ms

Figure 5.111 – Transparent bottom view of the monitor with only rear cover visible in green at time 20 and 25 ms

85 5.5.2.2.1 Energy balance

Looking at figure 5.112, it is possible to observe that the black and green modified curves are almost superimposed to the original case and so the change of the material respectively of the front frame and the rear cover of the monitor is negligible from the point of view of the energy balance. There is no shift, as expected and described before for the first point of impact with the change of material of the structural components of the monitor, of the point where the internal energy is equal to the kinetic one. The only small difference is highlighted in the red circle in the graph and is related to the breakage of the same threaded connection described in the original second point of impact. The breakage occurs slightly later in the case of the modified front frame made of PP TD20 with respect to the original case, as it is also shown in figure 5.113,

where at 9.8 ms there is not still breakage in the case of the modified front frame.

The second point of impact is located in the left end side of the monitor and since the structure of the front frame is prevalently on its end sides, the influence of the change of the material is more relevant. In this case, therefore, the delay of the breakage is caused by slightly higher stiffness of the front frame made of PP TD20.

Figure 5.112 – Energy balance comparison

Figure 5.113 – Frame of the threaded connection at 9.8 ms in the case of modified front frame (left) and original one (right)

86 5.5.2.2.2 Deceleration curve

Looking at the plot of the resultant acceleration in figure 5.114, the general requirement of FMVSS 201L regulations (limit = 80 g) and also the target requested by the car manufacturer (limit* = 64 g) are fulfilled.

Focusing on the integral of 3 milliseconds, the value of a_3ms curve with the modified front frame is, as expected, higher than the original case and similarly with the modified rear cover, where the highest value of the curve is reached due to the higher stiffness of the aluminum alloy.

5.5.2.2.3 Contact force between the impactor and the dashboard

Figure 5.114 – Deceleration curve comparison

Figure 5.115 – Comparison between curves of contact force between the impactor and dashboard

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Even in the graphs of the contact force in figure 5.115 it is possible to see that the curves are almost superimposed and so the influence of the change of the material of the structural components of the monitor is negligible from the point of view of head impact. The presence of two peaks in the plot of the contact force over the entire duration of the simulation, also with the modifications, is caused by the same phenomena that were described before in the original case of the second point of impact.