DYNAMIC ROPS TEST FOR TRACTORS OVER 6,000 KILOGRAMS
Document Type Article
© 2018 American Society of Agricultural and Biological Engineers
OECD static tests (Codes 4, 6, 7, and 8) for agricultural rollover protective structures (ROPS) have become accepted standards for evaluating the ability of these structures to protect the operator during tractor rollover events. The strength properties of some materials typically used in ROPS change because of cold weather embrittlement at low temperatures. The static ROPS tests lack the ability to evaluate the strength of these structures during cold weather. The use of the dynamic ROPS test is well noted as a means for proving cold weather embrittlement resistance properties. Unfortunately, application of the OECD dynamic ROPS test (Code 3) is restricted to tractors with unballasted mass greater than 600 kg and generally less than 6,000 kg. The analyses presented in this technical note were undertaken to evaluate the extension of the OECD Code 3 dynamic ROPS test to tractors with unballasted mass of 6,000 kg or more. Tractor unballasted mass and wheelbase data from 47 wheeled tractors tested at the Nebraska Tractor Test Lab from 2014 to 2016 were used to explore the possibility of using a dynamic test method for evaluating the ability of ROPS on tractors with unballasted mass greater than 6,000 kg to meet the safety requirements of agricultural tractor ROPS. The data were graphed and analyzed to determine the required pendulum drop height and energy values to be applied to the ROPS by extending the existing equations to tractors over 6,000 kg. For tractors over 6,000 kg mass, it was determined that pendulum drop heights were too great for practical use. Three pendulum masses were proposed for the dynamic ROPS test: a 2,000 kg pendulum for tractors with mass less than 7,000 kg, a 4,000 kg pendulum for tractors with mass of 7,000 kg or more and less than 14,000 kg, and a 6,000 kg pendulum for tractors with mass of 14,000 kg or more and less than 23,000 kg. Alternate equations were developed for the drop height of each pendulum to meet the energy requirements that are expected to provide similar permanent deflections as those obtained when using the static ROPS test when considering the effect of strain rates on material properties. Tests should be conducted to determine how the results (permanent deflections) from the proposed dynamic ROPS test compare with results from the accepted static ROPS tests. It is further proposed that dynamic testing be conducted with the tractor rigidly restrained in a manner similar to the static test to better account for the wide variety of available tires and mountings for each tractor model.