International Soil Tillage Research Organization

gage data wurt: recorded 011 a micrologge~' anti sobst:quently analyzed by amicrocompttter. T~IC experimellts €01. soil fracture studies were similarexcept 100 and 200 nlm operatinj: depth were selected.RESULTS AND DISCUSSIONForce Ili stri bution Predictjon: rigurn 2 illustratt!~ the typical forcedistrlbutio~~s for the chsel operating at a speed of 3.2 km/h and a depthof 305 mm for the plowed and oat stubble field. The t.esolts indicatethat for the plowed soil, tile force distribution was linear at both lowand high operating speecls nt a chjsel depth of 152.5 mm. (Glancey et al.,1988). The low and high speed tests io the plowed soil at a depth of 305mm indicated a hard layer located approximately 185 mm belorv the soilsurface as illustrated in Figure 2. In tile oat stubble field, tests withthe chisel operating at a depth of 305 mm indicated a unique kind ofbehavior when compared to the results from the plowed ground. Figure 2,at a chisel depth of 305 mm, indicate first, that there was no hard layeras in the plowed soil and second, that the force distribution was quadraticand not liuear.Soil Fracturr! Prequt?ncy Determination: The measllremenl. of the draftvariation on the chisel was achieved by monitoring only the top straingage (i.e. the strain gage furthest from the tip of the chisel). Figure3 shows a typical plot of the variation of soil cutting moment with time.A specially developed YFT routine was used to analyze the res111ts. Atypical FPT plot is shown in Figure 4. Results for each operating conditionwere pooled and the dominant fracture freqaencies were identified.The frequency for a given mode was then determined by pooling all thefrequencies from the different subsets for both replicates for that modeand then averaging them. Our results indicate that the soil failure processconsists of more than one dominant frequency. The results from thestubble soil il~dicate that there were three distinct fracture modes forthe tests run at 3.2 km/h and a depth of 100 mm. However. art increase inoperating depth to 200 mm eliminated the tllird fracture mode in the soil.This seemed not to be the case when operating at 0.8 km/h. When theoperating depth was increased from 100 mm to 200 mm at this lower speed,the fractures distances did decrease, however, the three distinct modesof fracture were still evident. In the plowed soil conditiolls at anoperating depth of 200 mm, only two fracture frequencies were dominant atboth opepating speeds. It appears that soil failure consists of bothmajor cracks as well as minor cracks. The major cracks seem, for themost part, to form ahead of the cl~isel (i.e. ill the direction of travel)while the minor cracks appear to form laterally off of the major cracks.This process was complicated by cracks that were already present in thesoil due to the shrinkage of the clay as the soil dried over the summer.CONCLUSIONSBased on this study, we reached the following conclusions:1) An instrun~ented chisel for use in tillage studies has been developed.2) The chisel can be used to successfully determine the variation ofcutting force over it's operating deptl~ using a mathematical modelthat incorporates a penalty function approach to obtain a physicallymeaningful solution using a constrained optimization technique.