Friction Induced Rollover from Lift-Off to Launch

A friction induced rollover event generally comprises successive stages of control loss, lift-off, transition from lift-off to launch, and roll to rest. This transition is, of course, not instantaneous due to vehicle inertia. It is analyzed by numerical integration of the equations of motion to determine roll angle and time to launch, plus roll velocity at launch, as well as intermediate values of roll angle, roll velocity and surface force versus time. Representative curves and launch values are presented. The time to launch, which is several times greater than typical vehicle collision contact time, is seen to be dependent on the magnitude of surface friction; while roll angle from over-center at launch and roll velocity at launch do not vary substantially with changes in vehicle and surface conditions. It is also seen that the surface force initially rises above static weight, producing lateral force greater than the friction coefficient times vehicle weight as rotation progresses. Models are presented for both hard surface and furrowing friction, with transition computation programs appended. Visually observed lift-off in dynamic roll stability testing is actually a point of rotation within the transition from lift-off to launch, typically involving an impulse with transient acceleration exceeding the rollover threshold. The transition analysis enables proper correlation between such test data and vehicle roll stability. An exemplar vehicle is analyzed; and a dynamic roll test acceleration trace for that vehicle is compared with the analysis to illustrate the method and accuracy of correlation.