Abdul Mounem Mouazen

Finite element analysis of subsoiler cutting in non-homogeneous sandy loam soil

Abstract A verified finite element model will be a cheap and useful tool in the development procedure of subsoilers and other soil loosening devices, and can be used to investigate and analyse the performance of resulting prototypes. This study was undertaken to emphasis that the finite element method (FEM) is a proper technique to model soil cutting processes in non-homogeneous soils. This method was used to investigate and analyse soil loosening processes. The effect of geometry on subsoiler performance was investigated by the FEM and compared to results of soil bin tests for four subsoiler geometry types; S1 – vertical shank with 31° angle inclined chisel, S2 – vertical shank with 23° angle inclined chisel, S3 – vertical shank with 15° angle inclined chisel and S4 – 75° rake angle shank with 15° angle inclined chisel. The research was done at the Department of Agricultural and Environmental Engineering, PANNON Agricultural University from 1995 to 1997. A three-dimensional FEM model was developed for cutting of non-homogeneous sandy loam soil by a subsoiler having a chisel and shank with different angles and effective cutting widths. The numerical analysis was performed with COSMOS/M 1.71xa0FEM software (Structural Research and Analysis Corporation, CA). The soil material was considered as elastic-perfectly plastic, and the Drucker–Prager elastic-perfectly plastic material model was adopted with the flow rule of associated plasticity. Soil-tool interaction was simulated adopting Coulombs law of friction. Total draught force calculated from the FEM model for different subsoiler geometrical types ranged from 12.43 to 15.32xa0kN. For the S2 subsoiler, that had a vertical shank and an inclined chisel of 23° angle, the chisel and shank contributed to the total draught force by nearly 60 and 40%, respectively. The FEM model consistently over-predicted the measured subsoiler draught force at all chisel angles. The over-prediction of draught estimation ranged from 11 to 16.8% for a non-homogeneous model and from 15 to 18.4% for a homogeneous one. The smallest draught force, measured (11.20xa0kN) and predicted (12.43xa0kN), was recorded for the S4 subsoiler having a shank of 75° rake angle and a chisel of 15° angle. The minor principal stress field showed positions of soil tensile failure situated beneath the chisel as well as within the upper soil layers. Zones under distortion (shear failure) were generated directly in front of the shank and along the whole cutting edge of the chisel extending along a hard pan layer. The S4 subsoiler would consume the least amount of energy and perform proper soil loosening. The FEM proved a good tool for modelling of non-homogeneous soils and development and analysis of subsoiler performance and soil loosening processes.

Two-dimensional prediction of spatial variation in topsoil compaction of a sandy loam field-based on measured horizontal force of compaction sensor, cutting depth and moisture content

Abstract The development of a topsoil compaction map, based on real-time measurement of the draught ( D ) of a compaction sensor provides a quick view of positions of extremely compacted zones. The measured D of a subsoiler, used as a compaction sensor was utilised to draw the two-dimensional spatial variation in soil compaction of a sandy loam field (Arenic Cambisol). On the basis of a previously developed formula, dry bulk density ( ρ d ) indicating soil compaction was estimated as a function of the measured horizontal force, cutting depth ( d ) and moisture content ( w ). This formula was the output of a numerical–statistical hybrid modelling scheme, which aimed to estimate the variation in sensor D as a function of w , d and ρ d . The ARCVIEW 3.1 GIS software was used to draw the field maps of measurement and model-based ρ d , d , w . The measurement and model-based ρ d ranged from 1343 to 1750 and from 1271 to 1523xa0kgxa0m −3 , respectively. The model-based ρ d was underestimated by a mean error of 14%. A comparison of measurement and model-based ρ d maps indicates a similar tendency of spatial variation in soil compaction, particularly positions of extremely compacted zones. This allows providing the farmer with a compaction map, which illustrates the extreme zones of soil compaction. A correction factor of 14% in ρ d is incorporated into the developed numerical–statistical model, which improved the magnitude of the model-based predicted soil compaction. Furthermore, the real-time measurement of w with better control of d might be helpful to improve the magnitude of ρ d predicted and spatial distribution of soil compaction.

A numerical–statistical hybrid modelling scheme for evaluation of draught requirements of a subsoiler cutting a sandy loam soil, as affected by moisture content, bulk density and depth

Abstract The development of simple regression relationships, based on finite element (FEM) analyses of cutting a sandy loam soil by medium–deep subsoiler will provide confidential and quick tools to predict the subsoiler draught requirement for any combination of moisture content ( w ), wet bulk density ( ρ w ) and tillage depth ( d ). Large number of FEM analyses were performed to assess the effect of w , d and ρ w on subsoiler draught. This draught was calculated from the output of 126 FEM modelling analyses. The model variations were selected based on the interaction among the studied variables, namely, six moisture contents ranging from 0.03 to 0.22xa0m 3 xa0m −3 , five wet bulk densities ranging from 1.3 to 2.0xa0Mg/m 3 and six tillage depths ranging from 0.10 to 0.37xa0m. The interaction among these three variables was also taken into consideration, and a multiple linear regression analysis was performed aiming at establishing a mathematical relationship for simulating the draught variation as a function of these variables. Further relationship was developed for relating the variation in draught with w , d and dry bulk density ( ρ d ). The FEM showed that subsoiler draught increased with d , ρ w and ρ d , whereas it decreased with w . The decrease in draught with w did not extend beyond a w of 0.17xa0m 3 xa0m −3 , since the draught calculated for 0.22xa0m 3 xa0m −3 w was very close to that calculated for a w of 0.17xa0m 3 xa0m −3 . Regression equations developed to relate the subsoiler draught with w , d , ρ w and ρ d were of quite simple forms, and had high determination coefficients ( R 2 ) close to 0.95. These equations indicated that the horizontal force varied linearly with w and non-linearly with d , ρ w and ρ d . This non-linear variation of draught was found to be a quadratic function of d and ρ w , and a cubic function of ρ d . A comparison of the calculated and measured draught for cutting a similar sandy loam soil with a similarly designed subsoiler, showed a good approximation. The small divergence between the calculated and measured draught was attributed to the difference in soil texture and subsoiler chisel length. Thus, the regression equation developed proved to be a capable tool of predicting the draught requirements of the selected tillage tool design, when cutting sandy loam soils under any combination of w , d and ρ w .

Modelling Compaction from On-line Measurement of Soil Properties and Sensor Draught

The finite element method was used to analyse the cutting process of a sandy loam soil with medium-deep subsoiler, used as a compaction sensor, aiming to calculate the subsoiler draught for various combinations of dry bulk density, moisture content and tillage depth. The finite element results showed that draught increased with depth and dry bulk density, whereas it decreased with moisture content. A multiple linear regression analysis was performed to establish a formula for relating subsoiler draught (dependent variable) with the three independent variables. The regression equation developed was simple and had a high determination coefficient close to 0.95. An equation for prediction of dry bulk density as a function of moisture content, depth and draught was derived from the regression equation developed. This equation was used to calculate dry bulk density, for measured depth, moisture content and draught at nine different points along a single line in a meadow field of a silty clay loam soil. The predicted dry bulk density indicated that there was a considerable variation in the degree of compaction throughout the measured line. However, the on-line depth control and measurement of moisture content still need to be integrated with the on-line measurement of draught, to govern the model suitability for performing on-line detection of the spatial distribution of soil compaction, assessed as dry bulk density.

Mechanical behaviour of the upper layers of a sandy loam soil under shear loading

Abstract The mechanical behaviour of the upper layers of a sandy loam soil was studied under standard triaxial compression and direct shear box tests. Variations of soil material properties were investigated at four different initial dry bulk densities of 1410, 1520, 1610 and 1670 kg/m3. Soil deformation and volume change under the triaxial compression loading were also studied at these bulk densities. Results from the two tests showed increases in the soil mechanical properties with the initial dry bulk density. The internal friction angle values measured with the triaxial compression apparatus exceeded those measured with the direct shear box. In contrast, the soil cohesion values measured with the direct shear box exceeded those measured with the triaxial compression apparatus. Under the triaxial compression test, the loose soil samples underwent contraction and volume reduction, whereas the dense samples swelled and failure cracks appeared clearly at various planes. The soil contraction for the former case characterizes the occurrence of soil compaction, whereas the cracks propagation and volume increase in the latter case characterizes the breaking up and loosening of soil during tillage operations. For the loose and moderately compacted states, the engineering Poissons ratio increased with the axial strain until loading was completed. It also increased at the compacted and very compacted states until reaching given loading stages, after which its value started to decrease. This shifting in the engineering Poissons ratio during loading may provide another identification of the moment of soil failure occurrence, in addition to that of the maximum shear stress.