Theoretical Head Impact Velocity & Post Impact Head Deceleration

Theoretical Head Impact Velocity & Post Impact Head Deceleration

The theoretical head impact velocity concept has been developed for assessing occupant impact severity for vehicles involved in collisions with road vehicle restraint systems. The occupant inside the vehicle is considered to be a freely moving object that, as the vehicle changes its speed due to the contact with the restraint system, continues moving until it strikes the vehicle interior. The velocity magnitude at the time of impact with the vehicle interior is considered to be a measure of the vehicle to vehicle restraint system impact severity.

After impact the head is assumed to continue moving with the vehicle during the rest of the impact event. The post impact head deceleration (PHD) is calculated as the peak value using a 10ms moving average of the resultant vehicle acceleration after the THIV impact.

The THIV calculation requires the following inputs Horizontal Vehicle Acceleration Time History (Ax) Lateral Vehicle Acceleration Time History (Ay) Yaw Rate Time History Horizontal Distance from the occupants head to vehicle (Dx) Lateral Distance from the occupants head to vehicle (Dy) Initial X coordinate relative to CofG (X0) The units for these fields should be consistent with the units that the model is in. For example, If the accelerations are in m/s2 then values for Dx, Dy and X0 should be in metres. The Yaw Rate Time History curve is expected to be in radians/s

For more information on THIV and PHD see BS EN 1317-1.