Randall K. Wood

Some Comparisons of Average to Peak Soil-Tire Contact Pressures

Comparisons are made among several methods of determining the contact pressure between a tire and the soil. Results show that on compacted soils the peak pressures measured at the soil-tire interface are much greater than mean pressures determined from measure-ments and much greater than pressures calculated by dividing the dynamic load by contact area. On uncompacted soil, peak pressures are almost equal to the inflation pressure.

Effects of soil and operational parameters on soil-tire interface stress vectors☆

Abstract Normal and tangential stress vectors were measured at the soil-tire interface of a pneumatic tractor tire on firm and soft soils. Stress magnitudes were determined with a transducer which was designed to measure both normal and tangential stresses. The orientation of the transducer was determined using a 3-dimensional, sonic digitizing system which was mounted inside the air cavity of the tire. Data are presented from tests conducted at zero input torque, zero net traction, and 0.15 net traction ratio which show the effects of inflation pressure, dynamic load, and soil conditions on the stress vectors.

Soil-Tire Interface Stress Measurements

ABSTRACT NORMAL and tangential stress vectors were measured at the soil-tire interface of a pneumatic tractor tire on firm and soft soil. Data are presented from tests conducted at zero input torque, zero net traction, and 0.15 net traction ratio. Peak normal stresses occurred before peak tangential stresses as the tire rotated through the contact area at 0.15 net traction ratio. A force balance was performed on the tire at each level of tractive performance.

A Three-Dimensional System for Measuring Tire Deformation and Contact Stresses

ABSTRACT Athree-dimensional, sonic digitizing system was adapted for use inside the air cavity of a pneumatic tractor tire to measure tire deformation and the directions of soil-tire interface stresses. The magnitudes of these stresses were measured with a system of pressure transducers. The stress transducers were mounted in both the lug and undertread areas of the tire surface. Data are presented which illustrate the type of information that can be obtained from this system.

Effects of Dynamic Load on Normal Soil-Tire Interface Stresses

ABSTRACT The effects of the tire dynamic load on the normal stresses at the soil-tire interface of a pneumatic tractor tire were investigated. Results showed that on loose soil, the normal stresses increased with increases in dynamic load. On firm soil, normal stresses increased with dynamic load near the outside of the tire, but decreased with dynamic load near the tire center.

Characterizing Soil Deformation by Direct Measurement Within the Profile

ABSTRACT Aunique feature of the University of Kentucky soil bin enables deformation to be characterized by studying a cross-sectional soil profile grid pattern. Modular sections of the bin are laterally removed to expose the cross-section after passes of a pneumatic tire. The measured displacements of the grid points were converted to values of volumetric strain and then compared to soil density as measured by a dual probe gamma-ray density gauge following tests at various soil conditions. Final soil bulk density determinations using the two methods were not statistically different..

Tangential-to-Normal Stress Ratios for Pneumatic Tires

ABSTRACT THE tangential-to-normal stress ratio at the soil-tire interface was determined for a pneumatic tractor tire operating on a variety of conditions. Results show that this ratio, at a point on a tire, increases linearly as this point advances through the soil-tire contact arc. The value of the ratio of tangential-to-normal stresses exceeded 1.0 at high values of travel reduction on a sandy loam soil.

Three-Dimensional Tire Deformation on Deformable Surfaces

ABSTRACTAsystem was devised to measure three-dimensional deformation of a pneumatic tractor tire at three positions across the tread width on both lug and undertread surfaces. Tire deformations were compared to measured radial and tangential stresses at the soil-tire contact surface. Results showed that maximum normal stress occurred at an angular position on the tire ahead of maximum radial deformation. Maximum tangential stress occurred at a tire angular position before maximum tangential deformation.

Dynamic Load Effects on the Tangential-to-Normal Stress Ratio for Pneumatic Tires

ABSTRACT The tangential-to-normal stress ratio at the soil-tire interface of a radial-ply tractor tire was investigated for a range of soil conditions and dynamic load values. Results show that soil type affects this ratio, but tire load has no consistent affect. Results also show that the tangential-to-normal stress ratio has a value greater than 1.0 at several locations on the surface of tire lugs. This high value of the ratio suggests that the soil strength parameters which govern traction have both frictional and adhesive components.