First impact point

The first step to observe the behaviour of the dashboard is to consider the frame of the head impact simulation every 5 ms up to 20 ms. In figure 5.77, 5.78, 5.79, 5.80 and 5.81 it is shown the simulation with the modified front frame while in figure 5.82, 5.83, 5.84, 5.85 and 5.86 the one with the modified rear cover.

In each figure is visible a full view of the entire dashboard and a left side section, located in the middle plane of the head impactor.

Figure 5.77 – Full view and left side section of the head impact with modified front frame (time 0 ms)

Figure 5.78 – Full view and left side section of the head impact with modified front frame (time 5 ms)

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Figure 5.79 – Full view and left side section of the head impact with modified front frame (time 10 ms)

Figure 5.80 – Full view and left side section of the head impact with modified front frame (time 15 ms)

Figure 5.81 – Full view and left side section of the head impact with modified front frame (time 20 ms)

Figure 5.82 - Full view and left side section of the head impact with modified rear cover (time 0 ms)

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Figure 5.85 - Full view and left side section of the head impact with modified rear cover (time 15 ms)

Figure 5.86 - Full view and left side section of the head impact with modified rear cover (time 20 ms) Figure 5.84 - Full view and left side section of the head impact with modified rear cover (time 5 ms)

Figure 5.83 - Full view and left side section of the head impact with modified rear cover (time 10 ms)

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Finally, in figures 5.87,5.88 and 5.89 it is shown a focus on the front frame of the monitor (yellow component) while in figures 5.90, 5.91 and 5.92 it is shown a focus on the rear cover (green component).

Figure 5.87 – Transparent bottom view of the monitor with only front frame visible in yellow at time 0 and 5 ms

Figure 5.88 – Transparent bottom view of the monitor with only front frame visible in yellow at time 10 and 15 ms

Figure 5.89 – Transparent bottom view of the monitor with only front frame visible in yellow at time 20 and 25 ms

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Figure 5.92 – Transparent bottom view of the monitor with only rear cover visible in green at time 20 and 25 ms Figure 5.91 – Transparent bottom view of the monitor with only rear cover visible in green at time 0 and 5 ms

Figure 5.90 – Transparent bottom view of the monitor with only rear cover visible in green at time 10 and 15 ms

78 5.5.2.1.1 Energy balance

Looking at figure 5.93, it is possible to observe that the black curves, where the dashboard presents the modified front frame of the monitor made of PP TD20, are almost superimposed and so the change of the material of the front frame of the monitor is negligible from the point of view of the energy balance. This is due to the fact that the mechanical properties of the original front frame made of PC+ABS and the ones of the front frame made of PP TD20 are very similar and in addition, this is not the first component to get in contact with the head impactor but, since it is located in the bottom part of the monitor, it affects the general behavior of the entire dashboard. There is not the shift of the point where the internal energy is equal to the kinetic one and this shift is not present also in the change of the material of the rear cover from magnesium alloy to aluminum one and so the effect of the change of material can be considered negligible

in this case.

Even if the stiffness of the rear cover made of aluminum alloy is higher than the one made of magnesium, the slope of the green curve of the internal energy is almost superimposed to the original one. The only visible effect on the plot is that the dashboard with the modified rear cover is able to absorb more energy in the impact phase and after the impact, when the head impactor returns back to its initial position, it is able to release back to the head form higher energy and this is in accordance with higher stiffness of aluminum alloy.

Figure 5.93 – Energy balance comparison

79 5.5.2.1.2 Deceleration curve

Looking at the plot of the resultant acceleration in figure 5.94, the general requirement of FMVSS 201L regulations (limit = 80 g) and the target requested by the car manufacturer (limit* = 64 g) are fulfilled.

Focusing on the integral of 3 milliseconds (a_3ms), it is more visible the effect of the material of the structural elements of the monitor. In fact, the value of a_3ms curve with the modified front frame is higher than the original case, due to the slightly higher stiffness of PP TD20 with respect to PC+ABS and a similar consideration can be done with the modified rear cover, where the effect of higher stiffness of Al alloy with respect to Mg alloy is more evident and the highest value of the curve is reached.

5.5.2.1.3 Contact force between the impactor and the dashboard

Figure 5.94 – Deceleration curve comparison

Figure 5.95 – Comparison between curves of contact force between the impactor and dashboard

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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.