Clarence E. Johnson

A Stress State Transducer for Soil

ABSTRACT Atransducer was developed that measured normal pressures in six predetermined directions to provide data for mathematically determining the complete stress state in soil. The stress state transducer was evaluated under hydrostatic loading in both a sand and a clay. All six sensing elements registered within 6% of the applied pressure.

A Soil Compaction Model for Cylindrical Stress States

ABSTRACT Asoil compaction model that includes soil behavior under compressive normal and shearing stresses great enough to attain maximum compaction was developed. The model was developed and verified with triaxial tests on several agricultural soils. This model predicts soil compaction under vehicle loads better than earlier models because the input stress state can more realistically represent field conditions.

Hydrostatic Compaction of Agricultural Soils

ABSTRACT A three-parameter multiplicative model for soil compaction was developed and evaluated using triaxial tests on two agricultural soils. The model satisfied the boundary conditions at low and high stress levels. The effects of moisture content on the three coefficients were investigated.

Soil Stress State Determination Under Wheel Loads

ABSTRACT TWO 6-directional stress state transducers were used to measure soil stresses beneath a moving tire in the soil bins at the National Soil Dynamics Laboratory. Principal stresses, stress invariants, and octahedral normal and shearing stresses were calculated from the measured stresses. The ratio of octahedral shearing to octahedral normal stress indicated high shearing action under the tire although the tire was developing no net traction.

A Force Dynamometer for Three-Point Hitches

ABSTRACT A three-point hitch accessory was designed and constructed to measure draft, vertical force, and torque simultaneously and independently in a vertical longitudinal plane caused by an implement. Special features of the force dynamometer are dual-loading range and fast-hitching capability. The force dynamometer is designed for tractors in the 75- to 100 kW power range with maximum draft capacity of 66,700 N in the dynamometers high-range and 36,000 N in the low-range.

A rationale for modeling soil compaction behavior: an engineering mechanics approach

ABSTRACT Modeling agricultural soil compaction is important as one input to a system of effective management of soil physical condition to improve crop production. The desired degree of compaction depends on the intended purpose; for example, the requirements for traction and mobility are quite different from those for infiltration and root propagation. Our goal is to develop a compaction model and related soil and soil-machine behavior models which can be used to design systems for effective management of soil physical condition. In this article we discuss our rationale in modeling soil compaction and related soil-machine systems. The status of the various modeling efforts is discussed, as are plans and needs for the future.

Energy in Clod-Size Reduction of Vibratory Tillage

The objective of mechanical manipulation of the soil (tillage) in production of agricultural crops is to produce soil conditions and environment favorable to crop growth by changing bulk density, soil-aggregate size distribution and other characteristics of the soil. Disciplines Agriculture | Bioresource and Agricultural Engineering Comments This article is from Transactions of the ASAE 12, no. 3 (1969): 371–374. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/abe_eng_pubs/220 Energy in Clod-Size Reduction of Vibratory Tillage C. E. Johnson and W. F . Buchele

Shear Measurement for Agricultural Soils — A Review

ABSTRACT SHEAR measurement methods and devices are reviewed and compared. Problems associated with shear measurement are identified and recommendations are given.

Soil Compaction by Continuous Deviatoric Stress

ABSTRACT Ahydrostatic compaction model for unsaturated soils was expanded to include continuously increasing deviatoric stress. The expanded compaction model was developed and evaluated using two types of load paths on triaxial test samples from four agricultural soils. The model satisfied the boundary conditions at low and high stress levels and predicted soil bulk density within 4 percent of measured bulk density.

COUPLING NORMAL AND SHEARING STRESSES TO USE IN FINITE ELEMENT ANALYSIS OF SOIL COMPACTION

A finite element model was modified to use a constitutive relationship of soil compaction that included the effects of both normal and shearing stresses. Predicted values of soil stress were compared against results from a laboratory experiment. All predicted values at final deformed depths less than 0.3 m were within the 95% confidence intervals of the measured values, but at deeper depths most of the predictions fell outside the 95% confidence intervals of the measured values.