NOIRS 1997 Abstracts of the National Occupational Injury Research Symposium 1997. Washington, DC: National Institute for Occupational Safety and Health, 1997 Oct; :46
The American Society of Agricultural Engineers (ASAE) is one professional society which has developed a standard for certification testing of rollover protective structures (ROPS) on agricultural tractors. Certification of a ROPS can be performed following static procedures in the current standard, ASAE S519. This research simulates rollovers about the rear axle and compares ROPS stress levels with stress levels found during simulated ASAE S519 static testing. The ROPS modeled in this simulation is representative of one that might be found on small tractors (~50 hp PTO) operated on a hillside. Modeling has been performed using finite element techniques. Variables describing the ROPS construction, such as part dimensions and materials, have been parameterized to allow rapid simulation of a variety of ROPS prototypes. Additional variables include the ground slope and the tractor's initial rotational velocity. For the current research, slope angles of 10, 30, and 60 degrees were examined. Initial rotational velocities included 1, 3, and 4 rad/sec. A slope angle of 60 degrees matches the slope recommended in ASAE S519 rear field upset tests. An initial rotational velocity of 4 rad/sec, when converted to a pure translation, is in excess of the speed recommended for the ASAE S519 rear field upset test. Initial analyses began the rear rollover model at 90 degrees to the ground plane since ROPS-ground contact occurs in the final 90 degrees of rollover. Furthermore, this initial position served to conserve computer time and storage space. For these simulations, it was observed that ground-impact induced stress levels recorded during rear rollovers were on average 19.4% lower than stress levels recorded during simulated static ASAE S519 testing. However, these simulations failed to identify slope angle as a major contributor to ROPS stress. The rear rollover model was modified to initiate the rollover at the point of no return, when the tractor center of gravity is vertically above the rear axle. Starting the simulation at this point will model the energy transfer during the overturn, from potential to kinetic, more accurately than the previous simulation. Preliminary examination of these data suggests the new simulation identifies a more pronounced slope angle effect on ROPS stress. Future work will include development of models for side rollovers based upon knowledge gained in rear rollover simulation work.