Comparison

5.3 – Chevrolet Silverado

Table 5.9: Chevrolet Silverado MPDB - intrusion measurements Direction or Intrusion

Position [mm]

Steering column

x -11

y -11.5

z -8.6

A pillar upper 0

lower 0

Firewall upper 33 - 81 passenger

lower 4 - 23 passenger

Door opening width - driver side upper 0

lower 0

Door opening width - passenger side upper 0

lower 0

Cross car beam - fixture point

x -4.1

y 2.3

z 3.1

Cross car beam - max deformation

x

-y

-z

Figure 5.57: Chevrolet Silverado - ODB vs MPDB energy content

acceleration, however, both show a value around 13g, as after the initial section in which the triggers work in a virtually identical way, the main rail is loaded much more quickly by the mobile barrier and the buckling of the mid section of the structure is restricted to around 15-20ms. This effect can be attributed mainly to the nature of the PDB, which is substantially stiffer and does not get penetrated as deeply as the ODB, inducing high enough loads earlier. Therefore, where the ODB causes a peak much higher, this effect is balanced in the average by a higher acceleration throughout the final 2/3 of the impact with the mobile barrier. Another substantial difference is represented by the time to zero velocity. The zero point is crossed after 113.2s in the current test, while it is not reached at all in the new procedure: the Silverado achieves a stable velocity of 2.1m/s after 101.5s and it does not decelerate further, accelerating the obstacle in reverse direction. The delta of velocity is therefore even lower than 13.8m/s.

The difference in energy and between the two procedures drives substantial disparity in the failure of the ladder chassis as in one test the rail fails heavily at the end of the crash underneath the cabin, while in the other it does not show any sign of damage in this area.

This, together with the loading on the engine, results in very different intrusion levels, as will be explained later in this section.

Table 5.10: Chevrolet Silverado - ODB vs MPDB dynamic data ODB MPDB Difference % Difference

Peak acc. [−g] 48.57 35.71 12.86 26.47

Mean acc. [−g] 13.39 12.92 0.47 3.51

Time to zero velocity [s] 113.20 (101.50) (11.70) (10.33)

5.3 – Chevrolet Silverado

Figure 5.58: Chevrolet Silverado - crash pulse comparison

Figure 5.59: Chevrolet Silverado - velocity trend comparison

(a) ODB

(b) MPDB

Figure 5.60: Chevrolet Silverado - main rail deformation comparison

5.3 – Chevrolet Silverado

Section forces

The comparison of section forces shown in Figure5.61supports what has been said above.

In fact, both the front part and mid part of the main rail show the same maximum level of force sustained before buckling, the main difference being the timeframe in which the loading and buckling occur. In addition, the mid part of the structure fails in three fast, consecutive instances when loaded by the mobile barrier, while in the ODB it loads slowly and fails once - the second time corresponds to the loading of the rear section. The real differences begin to show when looking at the just mentioned rear section and at the powertrain loading. The level of force sustained by the former part is considerably higher in ODB, with a difference of more than 110kN , which is more than enough to cause catastrophic failure. Similarly, a discrepancy of more than 160kN is registered for the powertrain loading, which justifies the completely different behaviour in terms of intrusion as the extra force is only counterbalanced by the cabin.

(a) Main Rail front (b) Main Rail mid

(c) Main Rail rear (d) Powertrain

Figure 5.61: Chevrolet Silverado - section forces comparison

Cabin deformation and intrusion

As anticipated above, the intrusion and cabin deformation levels show a large improvement in MPDB due to the reduced amount of energy carried by the engine block during the impact. In Figure 5.62 the difference is made evident by the extensive deformed area in the ODB, which affects not only the back of the central dashboard section but also the pedals, the footwell and the passenger footwell. The two figures could not be put on the same colour scale as the latter would result looking completely undeformed. It has to be remembered that, despite these results, the vehicle obtained a GOOD rating in IIHS moderate overlap test. The intrusion measurements reported in [56] match up with the model, hence proving that those are not overestimated. This means that the available space behind the instrument cluster is so large that the vehicle has been designed to absorb a large portion of the impact energy with the firewall itself. Clearly, this necessity will not be present if the Silverado will be tested in MPDB, if the front structures stiffness was to remain unchanged. In any case, the high deformation of the rails in the ODB test causes a number other issues, such as the deformation of the floor (overestimated) and the rotation of the A-pillar, which translates into a minor decrease in door opening width.

(a) OBD

(b) MPDB

Figure 5.62: Chevrolet Silverado - firewall intrusion comparison

5.3 – Chevrolet Silverado

In conclusion, it is clear that the reduced amount of energy of the test and the fact that the PDB, although being theoretically more difficult to load appropriately, allows the same level of axial buckling as the rigid wall behind the ODB create a more favourable situation for the occupant protection devices of the Silverado. This was in fact one of the expected results from the introduction of the mobile barrier test and will allow the manufacturers to modify the frontal structures in order to achieve the same or better -level of self protection achieved in ODB, while focusing more on the partner protection side of the matter. Partner protection is clearly the flip side of such optimal performance in occupant protection for this vehicle, as will be discussed in the next chapter.

Table 5.11: Chevrolet Silverado - intrusion measurement comparison

Direction or ODB MPDB Difference

Position [mm] [mm] [mm]

Steering column

x -6 -11 -5

y 24.3 -11.5 -35.8

z 7.6 -8.6 -16.2

A pillar upper -19 0 19

lower 33 0 -33

Firewall upper 100 - (193) 33 - (81) -77 - (-112)

lower 112 - (103) 4 - (23) -108 - (-80)

Door opening width - driver side upper 4 0 -4

lower 11 0 -11

Door opening width - pass. side upper -1 0 1

lower 1 0 -1

Cross car beam - fixture point

x -17 -4.1 -12.9

y - 2.3

-z - 3.1