i think the real issue is the change in momentum and the duration of the
impulse (given by the integral of the force over time). for example if the
force were constant , it would be just the change in momentum over delta
time. now the real damage is dependent on the delta momentum and one over the
time duration. frangable bumpers etc. spread the energy disipation over time
resulting in less force, hence less damage to the rest of the system,
including the occupants.