Nonporous State Research Articles

Densification of a porous body during hot extrusion

1. A theoretical analysis is made of the densification of porous, viscous Newtonian and non-Newtonian bodies during hot extrusion. Equations are derived expressing the variation of the pressure and discharge energy as functions of relative density, fluidity of the solid phase forming the porous body, the coefficient of elongation, and ram velocity. The equations are applicable also in the limiting case of hot extrusion of a nonporous body. 2. It is demonstrated that, with a porous body whose solid phase is incompressible, the nonporous state cannot be attained by hot extrusion, and the relative density of specimens grows with increase in the value of coefficient of elongation. 3. Published experimental data indicate that the equations derived correctly describe the process of hot extrusion of porous materials. Using data obtained for porous iron, it is shown that the hot extrusion ofγ-iron is accompanied by plastic flow with an energy of activation close to that for flow in dynamic hot pressing; the two processes also have the same index of nonlinearity of flow, n=4. 4. Equations are derived for the energy of extrusion of a porous body processed under dynamic conditions with shock loading.

Light scattering and pore surface in paper under dynamic compression

Pressure pulses of 8.2 × 107 dyn cm-2, each lasting for about 0.01 sec, were applied to paper, and the scattered light from it was measured simultaneously in order to study the response of pores in paper under dynamic conditions. During the compression phase the deformation in pore surface, i.e. the loss in fibre-air interface, is found to be linearly related to the square root of pressure, and the minimum pressure required to compress a paper to the non-porous state is estimated to be around 5 × 108 dyn cm-2, depending on the type of paper. The decompression curve, however, always follows a different path; thus, a cycle of compression and decompression shows large hysteresis. An approximate calculation is made of the energy loss per cycle, and this shows the associated temperature rise to be less than 1 degc. The delayed recovery from compression is large compared with the elastic recovery, but the permanent set is very small. Both the resistance of pores to compression and the energy loss per unit volume seem to be related to the paper density.