No description available.

No description available.

Thesis (M.S.)--Ohio University, August, 1989. / Title from PDF t.p.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: compaction; powder; ejection. Includes bibliographical references (p. 117-119).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 70-74).

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 254-257).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 120-129).

The contribution of plastic flow to overall densification of a powder compact during hot-pressing has been analysed. The basis of this analysis is the incorporation of hot-working characteristics of materials at elevated temperatures into an equation applicable to hot-pressing conditions. The empirical equation relating steady state strain rate to stress is ἐ = Aσn and for the densification of a powder compact, the strain rate [formula omitted] The particles are assumed to be spheres and four different packing geometric configurations: cubic, orthorhombic, rhombic dodecahedron and b.c.c. are considered. Taking into consideration the effective stress acting at the points of contact, the equations for the strain rate can be combined and arranged into another equation which is shown below:[formula omitted] where α₁ and ϐ are geometric constants and can be calculated from the packing geometry. 'A' and 'n' are material constants. D is the relative density of the compact, and ‘R’ is the radius of sphere at any stage of deformation in arbitrary units. Computerized plots of D vs t were obtained for lead-2% antimony, nickel and alumina. Experimental verification of these plots was carried out using hot-pressing data for lead-2% antimony, nickel and alumina spheres. The hot-compaction experiments were carried out over a range of temperatures for each material and under different pressures. The experimental data fitted well with the theoretical prediction for the orthorhombic model. However, a deviation at the initial stage of compaction was encountered in most cases. This deviation was explained on the basis of the contribution to densification by particle movement or rearrangement at the initial stage, which could not be taken into account in the theoretical derivation. The stress concentration factor i.e., the effective stress acting at necks between particles has been calculated. This was found to be very much higher than that previously used by other workers. The theoretical equation for the effective stress is [formula omitted]. This equation predicts an effective stress, which is more than an order of magnitude higher than that predicted by several empirical equations used previously. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

M.Tech.

We focus on single punch compaction of powder metals in hollow cylindrical geometries, and pay special attention to the effects of non-uniform initial density distribution on final green densities, the effects of density-dependent powder properties and pressure dependent coefficients of friction on the evolution of the pressure and density profiles during compaction, and the time variations of the force required for ejection after the compaction pressure is removed. In studying the effects of non-uniform initial density distribution, we extend the work of Richman and Gaboriault [1999] to allow for fill densities that vary with initial location in the die. The process is modeled using equations of equilibrium in the axial and radial directions, a constitutive relation that relates the axial pressure to the radial pressure at any point in the specimen, and a plausible equation of state that relates local density to the local pressure. Coulomb friction is assumed to act at the interfaces between the specimen and both the die wall and core rod. In this manner, we determine the axial and radial variations of the final density, the axial, radial and tangential pressures, and the shear stress. Of special interest are the inverse problems, in which we find the required non-uniform initial density distribution that, in principle, will yield no variation in the final green density. For incorporating the effect of pressure and density dependent powder properties, we employ a one-dimensional model that predicts the axial variations of the pressure and density. In this model, however, we incorporate the density dependence of the radial-to-axial pressure ratio, as well as the pressure-dependence of the coefficients of friction at the die wall and core rod. The density-dependence of the pressure ratio is based on the experimental measurements of Trassoras [1998], and the pressure dependence of the friction coefficients is based on the measurements of Sinka [2000] and Solimanjad et. al [2001]. In the course of this study, we focus attention on a Distalloy AE powder, and establish the relation between its compressibility and its radial-to-axial pressure ratio. Finally, we employ linear elasticity theory to model the ejection of the green compact. In the first phase, we model relaxation of the compact after removal of the compaction pressure as a misfit of three cylinders, representing the core rod, the compact and the die wall. The known input is radial pressure distribution at the conclusion of compaction, and the output is the corresponding radial pressure distributions that prevail after the compaction pressures are removed. In the second phase, we determine the variations with punch displacement of the ejection forces required to overcome friction at the core rod and die wall. The model includes additions to the friction forces due to the radial expansion (i.e. the Poisson effect) that occurs during ejection. Predictions of the model compare well to the experimental results of Gethin et.al. [1994].