Masters Theses

Date of Award

12-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Paul D. Ayers

Committee Members

Alvin Womac, William Hart

Abstract

The agricultural industry has one of the highest fatality rates of any industry in the U. S. This death rate is largely due to deaths caused by roll over accidents while on agricultural vehicles. The addition of a Rollover Protective Structure (ROPS) has aided in lowering these high fatality rates on full-size tractors. Studies have shown that death rates have been reduced by as much as 98% with the addition of rollover protective structures. However, a large number of older tractors still do not utilize a ROPS. This is due to the difficulty of designing and creating a mounting structure. To aid in elimination of this difficulty an evaluation engineering plastics to aid mounting structure fastening on older vehicles was conducted. The use of engineering plastics around axle housings may create a uniform mounting style, as well as, lower costs of aftermarket rollover protective structures for these vehicles.

Various strengths of plastics were examined through shear testing, scale model testing, compressive strength testing, and cost examinations. Materials examined were a steel-filled epoxy, a fast curing steel-filled polyurethane, and an iron oxide-filled epoxy. The iron oxide-filled epoxy was chosen based upon strength and cost. This material showed the highest shear strength, 28.6 MPa, and compressive stress resistance. Compression testing of this material showed that it had an ASTM D695 unconfined compressive strength of 82.1 MPa and a compressive index of 157.1 MPa/mm. This material was also the least expensive at $0.06 per cubic centimeter of epoxy.

After material selection, testing of the plastic's strength was conducted through axle housing torsional loading, static ROPS loading tests, and field ROPS loading upset testing. To fulfill these tests an axle housing and plastic filled box was needed. Allis Chalmers D-17 axle housings were chosen due to this tractor still having a high number of tractors in use, estimated to be over 41,000 in 1993. In addition, there currently are not any commercial rollover protective structures available for this tractor. And, previous studies have been conducted that show D-17 axles could withstand ROPS loading.

Plastic filled boxes were designed to be a two part box that fit around the axle housing and sealed shut. Box dimensions were 25.4 cm long by 15.2 cm wide by 21.6 cm tall. Tops of all boxes produced had two 2.54 cm holes that allowed for plastic materials to be poured into the boxes.

Torsional axle housing and plastic filled box tests revealed that the torsional strength of the ROPS mount and axle housing combination had higher strengths with less twisting than the axle housing alone. Peak compressive stress on the axle housing with box was 62 MPa at 12.3 degrees of angular rotation. Previous researchers testing of a D-17 without a plastic filled box showed a peak compressive stress of 57.8 MPa at a angular rotation 18.3 degrees.

Next, a mounting structure was tested through static ROPS longitudinal and lateral tests done in accordance with SAE Standard J2194. From these tests, it was found that mounting structure and ROPS withstood energy requirements at ROPS deflections of 22.3 cm longitudinally and 16.3 cm laterally at the ROPS top. These values are well below the 41.5 cm longitudinal and 40.0 cm lateral calculated maximum allowable deflections needed to keep the ROPS from intruding into the operator's zone or exposing the operator's zone to the ground.

The final test conducted was a longitudinal field upset test. This test placed a plastic mounting structure on to a remotely operated D-17 tractor ballasted to normal operating weight, 2,118 kg. This tractor was then tested in accordance to SAE J2194 field upset test requirements. Results from this test show a passing of the standards requirements since ROPS deflection was 8.2 cm. Again well below the maximum allow longitudinal deflection of 41.5 cm.

An engineering plastic ROPS mounting system did withstand the forces applied during the static longitudinal and lateral ROPS tests. Field upset testing revealed the mounting system could withstand impact loads seen during actual upsets without a failure of the mounting system. During both static testing and field upset testing no permanent twisting of the mounting system was found. Since the mounting structure using engineering plastic showed no failures or permanent deflections during any testing and fulfilled all standard testing requirements, this system could be a viable option for a universal mounting structure for older tractors lacking an aftermarket ROPS. However, this study did not evaluate any weathering or degradation of the plastic material. Studies on how engineering plastic materials change after being introduced into weathering influences such as temperature extremes and cycling, UV light exposure, vibrations, and agricultural chemicals is needed.


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