Tractor rollover protective structures (ROPS) have been found effective for protecting people from serious injury or death when tractors overturn. Extension agricultural engineers and safety specialists are promoting the retrofitting of ROPS on pre-ROPS tractors. ROPS, meeting to ASAE standards, are available for these older tractors. However, effective protection not only depends on the proper design of ROPS, but also on the structural adequacy of the rear axle housing on which ROPS are mounted, and on the means of attachment. Adequate information on the strength of pre-ROPS tractor axle housings 1s still lacking. A research project to develop a technique for determining the suitability of tractor axle housing when adding ROPS to pre-ROPS tractors was initiated by the Biological Systems Engineering Department at Virginia Tech in 1991. A finite element procedure was developed for the rear axle assembly of John Deere 720 tractor and models were built with a commercial software ANSYS Engineering Analysis Program. The models were employed to analyze the stress distributions under the static, crush, and dynamic ROPS tests recommended by ASAE. Laboratory tests were conducted to validate the models, and to assess the suitability of the shell element model and the general solid element model. Results of the analyses show that the rear axle housing assembly of John Deere 720 tractor has a safe margin for the static and crush tests under the condition of this study. Results also show that can support the dynamic test if the ROPS is mounted with a larger contact area with the axle assembly. The study concluded that the finite element procedure is effective to assess the strength adequacy of tractor axle housing and to determine the feasibility of retrofitting ROPS on pre-ROPS tractors. / Ph. D.

Agriculture consistently ranks as one of the most dangerous occupations based on an overall work death rate. Tractor overturns, by far the single largest cause of death on farms, account for approximately 19% of all on-farm deaths. The concept of a Roll-over Protective Structure (ROPS) came into existence in 1971 and is designed to form a protection zone for the operator. However, the only way that the operator will stay in the zone is by using a seatbelt or other restraint system. A survey on tractor seatbelt usage was undertaken. Results indicate that only 13% of operators wear seatbelts half or more of the time and 61% report never wearing one. The reasons for these practices are a combination of factors: too much inconvenience, time consuming, an old habit of not wearing one, and a feeling that there is no danger. However, even in the face of such negativity, the survey revealed that 65% of the operators were neutral or approved of the idea of an automatically closing seatbelt. An automatically closing restraint system prototype was designed and built. The system was found to be costly ($560.00) and the potential for mass retrofitting was found to be very limited. However, an automatically closing seatbelt seems to be a viable solution to the problem of operators being unwilling to use the seatbelts provided. / Master of Science