ODB test

Front structures behaviour

The frontal part of the Accord, as expected, works very differently compared to the Yaris, sharing the impact on multiple load paths thanks to the ACE layout. During the first 15ms, the cross beam deforms and starts pushing on the crash box; at the same time, a level of controlled deformation is visible on the fixture point of the main rails on the firewall, hence the whole frontal section moves backwards without getting damaged. A portion of load is transmitted by the cross beam to the rhs main rail, as it is initially loaded and fails at the attachment point with the firewall. After this initial phenomenon, the crash box is loaded axially to its maximum strength and buckles almost perfectly. Consequently, the main rail is loaded again and shows the first failure: due to its variable cross section, the weakest point corresponds to the thinnest section, located slightly in front of the firewall.

At the same time, the upper load path starts bending inwards. The following 20ms see the consequent collapse of the main rail in two other points, further towards the front of the vehicle, as the initial collapse does not make the structure bend, maintaining it straight and forward facing. The points of failure are again corresponding to the changes in cross section. The engine cradle is now reached by the barrier and its mountings fail, sliding the cradle backwards without damaging the floor of the cabin. When the room for motion has ran out, due to the engine hitting the firewall, the front part of the support is loaded as well and bends upwards.

At 60ms, after further pushing on the barrier, the several failure points of the main rail make it bend out of shape completely - partly downwards and outwards, partly inwards;

the upper structures fail bending downwards and the whole frontal part is at this point a flat and compact metal shield pushing on the remaining branches of box section.

Figure 5.30: Honda Accord ODB - simulation snapshot

5.2 – Honda Accord

In the final stages of the crash, the shortening of the engine compartment causes the engine to push with more energy on the firewall, causing it to deform slightly in its top part. However, at this point the amount of energy left is not enough to cause major failures.

Finally, the wheel, which has been pushed outwards during the event by the deformation of the upright mounting points, is squeezed between the barrier and the sill and the whole structure of the cabin lifts by a few tens of mm. One important factor to be noted is that the vehicle never punctures the barrier, but makes use of two thirds of the honeycomb’s width compacting it evenly. The vehicle bumper, main structures and the bumper element of the barrier remain in line for most of the impact, pushing one on the other. Furthermore, at the end of the crash the upper structures still have a branch which has not been crushed, while the space in the engine compartment is reasonable. These two final consideration show that, overall, the ACE system seems to work properly both for occupant and for partner protection. This will be further emphasized by the level of intrusions explained in the next subsection and by the partner protection analysis in Chapter6.

Figure 5.31: Honda Accord ODB - structural collapse detail

Intrusion measurements

With regards to intrusion levels, the Accord performs well as the deformations occurring do not substantially diminish the survival space inside the cabin. The only two measurements of intrusion which seem to be worth discussing are the deformation of the firewall and the movement of the steering wheel. Starting from the latter, it is noted that during the impact the lower joint of the steering column, placed in correspondence with the exit through the firewall towards the steering rack, fails due to the deformation of the rack itself. This stops the steering wheel being pushed towards the driver, but allows a certain degree of movement of the whole column in other directions. Therefore, under the acceleration of the impact, the column pivots around the cross car beam, changing by a few centimetres the positioning of the airbag.

The most relevant deformation, however, affects the firewall. The highest levels of intrusion are found in the top half of the metal sheet, where the main rail is supported and connected to its underfloor continuation. As highlighted in the previous section, the initial and unsubstantial denting occurs quite early in the event. The pushing continues for the entire duration of the crash, hence there’s a slow and progressive deformation.

Although the maximum reached is around 100mm, this does not compromise the space available for the driver or the movement of the cross car beam, hence it is supposed that the dashboard would not move substantially as well. The design of the cabin makes it so that the space between the beam and the firewall is generous, allowing the firewall’s central parts to deform without pushing directly on other components. In addition, the point of attachment of the pedals does not correspond with the restricted area undergoing heavy deformation, therefore their movement is virtually null. Nonetheless, the behaviour here described should be verified by conducting a simulation on a model containing all the interior components to verify that what is here hypothesized occurs effectively. Considering the lower part of the firewall, corresponding to the footrest area, the intrusion level is very low, with the area of maximum being deformed by 10-12mm. Moreover, it has to be noted that the passenger side of the firewall is also deformed due to the impact with the engine:

the intrusion is located in the area behind the dashboard and reaches values of 50mm.

The last aspect to point out regards the windshield, which gets shattered by the impact with the bonnet. The sheet metal is pushed from the front backwards and the deformation achieved does not stop the latches from lifting and pushing it into the glass, causing an unwanted effect and some intrusion as well. It has to be noted that the dynamics of deformation of the latches appeared to be different from reality in the correlation study, hence this could be an issue caused by the model.

Figure 5.32: Honda Accord ODB - firewall deformation

5.2 – Honda Accord

Table 5.5: Honda Accord ODB - intrusion measurements Direction or Intrusion

Position [mm]

Steering column

x -3

y 13.3

z 31.6

A pillar upper 1

lower 5

Firewall upper 101

lower 12

Door opening width - driver side upper 4

lower 3

Door opening width - passenger side upper 1

lower 0

Cross car beam - fixture point

x 1

y 3

z -5.6

Cross car beam - max deformation

x 2

y 2.7

z 0.8