Simulation and experimental validation of tractor overturning and impact behaviour

Roll-Over Protective Structures (ROPS, safety cabs or frames) are required by law on agricultural tractors in the UK and many other countries to prevent drivers being crushed in overturning accidents. The research reported was aimed to help in the development of ROPS design and strength test criteria through a better understanding of the dynamics of overturning and estimation of the energy absorbed in the ROPS. A survey of overturning accidents showed the types likely to result in the greatest ROPS damage: (i) an overturn down a steep bank more than 2m high; and (ii) a multiple roll accident. A mathematical model of sideways overturning was developed. Equations describing the relationships between the forces and deflections at each point of contact between the tractor and the ground allowed the same model to cover tyre behaviour during overturning, and ROPS, wheel and soil behaviour during impact. A computer program based on the model was able to simulate both bank and multiple roll overturns. [Continues.]