Measuring soil compaction and soil behavior under the tractor tire using strain transducer

Soil compaction can occur due to machine traffic and is an indicator of soil physical structure degradation. For this study 3 strain transducers with a maximum displacement of 5 cm were used to measure soil compaction under the rear tire of MF285 tractor. In first series of experiments, the effect of tractor traffic was investigated using displacement transducers and cylindrical cores. For the second series, only strain transducers were used to evaluate the effect of moisture levels of 11%, 16% and 22%, tractor velocities of 1, 3 and 5 km/h, and three depths of 20, 30 and 40 cm on soil compaction, and soil behavior during the compaction process was investigated. Results showed that no significant difference was found between the two methods of measuring the bulk density. The three main factors were significant on soil compaction at a probability level of 1%. The mutual binary effect of moisture and depth was significant at 1%, and the interaction of moisture, velocity, and depth were significant at 5%. The soil was compressed in the vertical direction and elongated in the lateral direction. In the longitudinal direction, the soil was initially compressed by the approaching tractor, then elongated, and ultimately compressed again.     

Soil compaction management: Reduce soil compaction using a chain-track tractor

Modern agricultural production requires research for new design and layout plans of the track-chained mover, providing a reduction in soil compaction. One of many ways to improve the efficiency of machine-tractor aggregate (MTA) use is to improve the geometry of the support part of the chain-track tractor. Flat geometry of the support part of a chain-track tractor with a semi-rigid suspension creates maximum pressure on soil with the first and last track rollers, which causes increased soil compaction. Research objective is to ensure the uniform pressure on soil from the tractor with a semi-rigid suspension by justifying the geometry of the supporting part of the track-chained mover.Based on experimental and theoretical studies a model of pressure distribution along the length of the support part was developed. Thus, the geometry of the support part of a track-chained tractor with a semi-rigid suspension was substantiated. Pressure decrease on soil and compaction reduction are achieved by changing the geometry of the support part and rational location of the tractor mass center. To achieve the elliptical geometry of the support part of a track-chained tractor with a semi-rigid suspension lower track rollers were placed at different heights.To test the formulas and to study the influence of the support part geometry, of the hitch height and the force on the hook of a track-chained tractor on soil compaction, experiments were conducted. As a model for experiment, the tractor actively used in agriculture was modernized; chain-track tractor T-170M1.03-55 with flat and elliptical caterpillar bypasses. The pressure was measured directly by pressure sensors that were placed into the ground. Soil density in the track left by a track-chained tractor mainly depends on mover pressure and the number of impacts per pass. Track-chained mover makes two impacts on soil with the flat support part. If the support part geometry is changed, the number of impacts on soil is reduced to one. To create typical working conditions for T-170M1.03-55 track-chained tractor the third and fourth support rollers should be lowered by 9.5 ± 1.5 mm, the second and fifth-by 4.5 ± 0.5 mm relatively, which leads to a decrease in the maximum pressure on soil and reduces its compaction in the track left by the mover by 15–25%.     

Soil vehicle relationship: The peripheral force

During the past decades the author has continually worked on and perfected his conception of the interaction between the soil and the wheel. First, this work is summarized in this paper. The author then describes his conception of the mechanical interaction between them and clarifies the connection between the kinematic and dynamic processes that take place when a tractor is exerting pull. He shows by means of his kinematic model how the peripheral force is developed. Finally, he derives the appropriate equations for the computation of the peripheral force and the drawbar pull for both two-wheel-drive and four-wheel-drive tractors. Practical experience has proven that the concept is correct and the method is practical.     

A physico-mechanical approach to modeling of metal forming processes—part I: theoretical framework

A combined physico-mechanical approach to research and modeling of forming processes for metals with predictable properties is developed. The constitutive equations describing large plastic deformations under complex loading are based on both plastic flow theory and continuum damage mechanics. The model which is developed in order to study strongly plastically deformed materials represents their mechanical behavior by taking micro-structural damage induced by strain micro-defects into account. The symmetric second-rank order tensor of damage is applied for the estimation of the material damage connected with volume, shape, and orientation of micro-defects. The definition offered for this tensor is physically motivated since its hydrostatic and deviatoric parts describe the evolution of damage connected with a change in volume and shape of micro-defects, respectively. Such a representation of damage kinetics allows us to use two integral measures for the calculation of damage in deformed materials. The first measure determines plastic dilatation related to an increase in void volume. A critical amount of plastic dilatation enables a quantitative assessment of the risk of fracture of the deformed metal. By means of an experimental analysis we can determine the function of plastic dilatation which depends on the strain accumulated by material particles under various stress and temperature-rate conditions of forming. The second measure accounts for the deviatoric strain of voids which is connected with a change in their shape. The critical deformation of ellipsoidal voids corresponds to their intense coalescence and to formation of large cavernous defects. These two damage measures are important for the prediction of the meso-structure quality of metalware produced by metal forming techniques. Experimental results of various previous investigations are used during modeling of the damage process.      

A physico-mechanical approach to modeling of metal forming processes—Part II: damage analysis in processes with plastic flow of metals

A damage analysis is presented for the extrusion of a case-shaped cylindrical part by using a physico-mechanical approach for modeling metal forming processes. Two integral measures related to the hydrostatic and deviatoric parts of the damage tensor are used for the calculation of strain damage. The combined use of two damage measures in contrast to only one allows us to assess not only a risk of macro-fracture of the deformed material but also the stage of formation of large cavernous defects due to coalescence of ellipsoidal voids. Such a refined prediction of the actual quality of the material’s micro-structure is important when producing metalware that is supposed to operate under intense loading and thermal conditions. In case study of this paper the kinetic equations of damage are solved by using mutually consistent fields of stresses, flow velocities, and strains. It is shown that the predicted damage is less than its permissible value since a high hydrostatic pressure in the plastic zone heals the micro-defects, prevents their growth, and, thereby, increases the processing ductility of deformed metals during extrusion.