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A prediction model based upon Mohr-Coulomb soil mechanics theory has been developed to predict the interaction between the soil and agricultural discs of different geometries and operating angles to both vertical and tilted discs. The model is based on two forms of soil failure. The magnitude of each form of failure is depen- dent upon a passive reaction on the concave side of the disc and a vertical bearing reaction on the convex side of the disc. The predicted results are in close agreement with the results of the experimental studies. Disc geometry is one of the most important factors to be considered in evaluating the soil reaction acting upon a disc tool. A theoretical analysis of the disc geometry was therefore carried out. The analysis of the disc geometry makes it possible to determine the factors required for the predicted forces acting on a disc tool. The experimental studies were conducted in a sandy loam soil at a moisture content in the friable range, under controlled soil bin conditions. The work was carried out at full-scale with 3 dimensional force measuring apparatus developed primarily for this investigation. The discs studied had a range of disc angles between 150 and 600 and a range of tilt angles between 0 and 35. The depth of cut ranged from 80 mm to 140 mm and at speeds between 0.75 m/s and 1.5 m/s. The disturbance area of the soil caused by the rotating soil cutting disc is calculated to define the disturbed area for any combination of disc angle, disc diameter, gang spacing and depth of work in order to accurately calculate specific resistance. Disturbance and soil inversion were investigated using transparent discs and soil tracers, with a variety disc and tilt angles in order to quantify inversion and mixing.

The work presented in this thesis is part of and continuation of the work carried out by the author on the Mechanics of Power Hacksawing, on behalf of a hacksaw blade manufacturer. Process parameters which influence the metal. removal rate during power hacksawing have been identified and thus a detailed explanation of the basic sawing mechanism-suggested. Power hacksaw machine characteristics have also been investigated. The problem of blade testing is discussed. A method for assessing the blade performance is proposed which is based on metal removal rate but is independent of the machine characteristics. This could be 'used as a quality index for power hacksaw blades. This performance index is found to vary with workpiece breadth and tooth pitch. A theoretical model is used to give some explanation of this variation. iiowever, there is evidence that the gullet size and goemetry arc, more significant factors influencing the variation in blade performance with changes in the breadth of the workpiece and pitch of the blade teeth. Examinations of saw blade teeth have revealed that they have large cutting edge radii compared to the layer of metal removed, indicating that saw blades are basically blunt tools. The cutting action of tools with large cutting edge radii has been investigated and extensive simulation tests have been undertaken. From the observations of the chip formation mechanism and measurements of the relative position of the tool and machined surface during cutting, some new light is thrown upon the ploughing process. A slip-line field is proposed which qualitatively represents the assumed chip formation mechanism under steady state cutting conditions. The application of an empirical relationship between the chip tool contact length and the undeformed chip thickness in conjunction with the slipline field, provides quantitative correlation with the test results of a single point tool and qualitative correlation with a hacksaw blade.

Extrusion honing is a technique used for the finish machining of engineering components. The process may be used to deburr, radius or polish depending on the specific application. Extrusion honing utilises a polyborosiloxane polymer, which is mixed with fine abrasive particles and forced through or around components using an extrusion honing machine to achieve the machining action. It is evident that the machining process is very dependent upon the physical and mechanical characteristics of the polyborosiloxane. However, the process to date has largely been developed empirically, and further developments will require a greater understanding of the relationship between the characteristics of the polymer and the machining action. The rheology of the C-11 polyborosiloxane has been investigated using a concentric cylinder, a slit-die and a capillary rheometer. The shear history of the polyborosiloxane prior to testing with the capillary rheometer was found to significantly affect the results produced. At shear strain rates up to 100 s-1 and a temperature of 30°C the rheology of the polyborosiloxane has been approximated to a power law equation (K.=989KPas; n=0.935). At shear strain rates greater than 100 s-1 the pseudoplasticity of the polyborosiloxane increases significantly. Using this power law equation the velocity, shear strain rate and the shear stress within the polyborosiloxane in an extrusion die has been modelled mathematically. In some cases the extrusion barrel pressure and the mass flow rate through the extrusion die have both been shown to vary considerably during the constant ram velocity extrusion of polyborosiloxane in the capillary rheometer. It is tentatively proposed that such variations in the extrusion barrel pressure during capillary flow are a result of periodic slipping and sticking of the polyborosiloxane to the extrusion die wall. This mechanism is thought to be considerably influenced by the polyborosiloxane temperature, the extrusion ram velocity and the flow passage geometry. It is proposed that the measured variations in the mass flow rate of the polyborosiloxane through the extrusion dies are a result of pressure induced density variations within the extrusion barrel. This mechanism has been mathematically modelled. Temperature profiles within the C-11 polyborosiloxane have been measured on an extrusion honing machine and the results suggest significant heat generation towards the periphery of the restriction. These results have been used to model mathematically the heat generation and transfer within the polyborosiloxane during operation of the extrusion honing machine. It is proposed that heat generation during extrusion honing is by friction at the medium/workpiece interface and internal shear within the medium. Both of these mechanisms would cause the greatest heat generation towards the periphery of an orifice restriction.

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