After frontal impact, lateral and oblique side impact collisions are the
second most common cause of serious motor vehicle accidents. Side impact
collisions differ from frontal impacts in that there is direct
interaction of the occupant with the vehicle structure. It is not
uncommon for the door of a car to be pushed more than two feet (0.5 m)
into the vehicle interior.
With the adoption of side impact protection standards in both the United States
and Europe, vehicle side structures have been beefed
up quite a bit compared to previous generation vehicles. To further
cushion the blow of a side impact collision more and more car makers are
introducing side impact airbags. These deploy inbetween the occupant and
the vehicle structure to increase the duration of the contact and lower
the peak forces acting on the occupants.
||The industry makes extensive use of computer analysis during the
development of a new vehicle for both structural improvements as well as
for the development of side airbags. These models range from coarse
beam models in the early stages of development to detailed Finite Element
models in the latter stages. The coarser model allows analysis of the
overall kinematics of the impact as well as the relative velocities of
the door and the occupant.
|This gives design guidelines for the structure of the vehicle and
padding needed to protect the occupant. This then helps to build
the model for the more detailed study. Finite element models of
both the dummy and the door structure are used to study the interaction.
These analyses are of a complex nature as they involve large plastic
deformations as well as foam paddings that have complex non-linear
The effects of the various changes are studied by looking at the resulting
dummy injury measures. Rib acceleration, thoracic viscous injury level,
and pelvis acceleration are all indicators of the risk of serious injury.
If the car maker is not satisfied with the injury mitigation level that can
be achieved with structural improvements alone, he may decide to add a side
airbag to the list of standard equipment.
||The development of the side airbag starts on the computer as well and then
propagates to sub system testing on a sled. Different types of side airbags
can be analyzed for their protective characteristics. Some provide only cushioning
in the area of the vulnerable ribs, others include head protection as well.
To reduce the risk that the deploying side airbag induces injuries to the
occupant, the deployment is in general aimed away from the normal seating position.
Side airbags are not nearly as large and as powerful as the frontal airbags.
Nevertheless, extensive testing with out-of-position adult and child dummies
is necessary to ensure minimal risk of induced injuries.