Forensic Engineering Analysis of a Failed ROPS

Abstract

Agricultural, commercial, and some lawn and garden tractors have been known to tip and roll over. Roll-over protective structures (ROPS) are designed to assure seat-belted occupants can survive in a zone of clearance within the structure, during and following a roll-over event. Within the laboratory testing parameters established in the current standards, energy absorption is based on tractor mass alone, apart from any other forces that may be acting on the tractor. Current standards allow tractor manufacturers to determine the “reference mass” used for ROPS testing. Most manufacturers fail to include the mass of any attached implements. When implements remain attached to the tractor throughout the roll-over event, ROPS should still be designed to protect operators. In the past, tractors were mainly employed in soil-engaging or surface-grooming exercises. The center of gravity (CG) of these attached implements was relatively low. Today, however, tractors may tow larger, taller, and heavier implements with high CG on multiple axles, such as large liquid manure tank spreaders. The purpose of this paper is to investigate the physical issues associated with tractors towing high CG implements, such as geometrically tall, articulated steerable axle spreaders operating in sloped terrain that cause an ROPS to fail.