Vertical stress distribution rules in compacted topsoil under tire with chevron tread pattern

Stress distribution is produced due to the tire in the compacted topsoil under the chevron tread pattern tire, and it is one of the important considerations of soil-tire interaction research. It influences trafficability, ride performance, and traction performance of the tractor. In view of the serious compaction under the tractor which led to the bad trafficability, a vertical stress sensor test system was used to measure the vertical stress under 3 tire loads, 3 tire inflation pressures, 3 driving speeds, and determine the influence of these 3 parameters on the vertical stress in the topsoil. The vertical stress sensor test system was mainly made up of a group of piezoelectric type pressure sensors, a group of amplifiers, data acquisition card, power, and computer. Then, based on the multiple linear regression, a prediction equation was developed between the vertical stress, and tire load, tire inflation pressure, driving speed, the lateral and longitudinal distance from the tire centerline to the sensor. In the end, the influence of tire load, tire inflation pressure, driving speed and the lateral and longitudinal distance on vertical stress was analyzed in detail based on the prediction equation we developed, and this analysis result was contribute to understanding of compaction processes. All the experiments were conducted in a single tire soil-bin testbed which was self-designed and constructed, and all the sensors were installed 50 mm under the soil surface. 18 stress sensors were used under every condition. 6 stress sensors mounted at 3 positions across the lugs and undertread was made up for one group, and it was used to determine the vertical stress across the lanteral of the tire. 3 group stress sensors mounted at 3 positions across the driving direction of the tire which used to determine the vertical stress across the longitudinal of the tire. The main results indicated that: 1) When tire inflation pressure was 69 kPa, the soil-tire interface vertical stress curve became smooth and the peak value of vertical stress moved to a quarter to edge of the tire gradually, whereas, when the tire inflation pressure was 138 and 207 kPa, the peak stress value occurred in the center of the tire; 2) The maximum error coefficient between the predicted vertical stress value and actual vertical stress value was 10.59% while the mean error coefficient was 5.87% which showed the prediction equation we developed had certain predictive ability under our experiment condition, and the prediction equation indicated that tire load influenced vertical stress significantly, and followed by tire inflation pressure, driving speed, lateral distance, and longitudinal distance; 3) For the single factor, the vertical stress in the topsoil varied as a quadratic function of the tire load, longitudinal distance, and lateral distance, and it varied as a linear function of tire inflation pressure, and driving speed; 4) The value of vertical stress under the lug was 1.2-2.3 times larger than the value under the tread, and the farther from the tire centerline, the greater the influence of the lug. This research may provide the analysis theoretical basis for tractor trafficability, and decreases the soil compaction by adjusting the value of the influence factors.