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.