The paper presents the results from computer simulation and analysis of experimental data on the densification of copper and iron powder billets during hot shock compaction. It is established for the first time that the shear viscosity of the porous material matrix shows a stronger dependence on the initial impact velocity than the billet temperature does. The estimated activation energy of the viscous flow in the matrix is equal to 0.35 eV for copper, 0.3 eV for α-Fe, and 0.5 eV for γ-Fe.Hot shock compaction is an efficient method for thermomechanical treatment of porous materials which is widely applied to produce high-density and high-strength parts from metal powders [1-2]. It is a dynamic process in a mechanical system with one degree of freedom that consists of an impact machine and a deformable powder body [3]. When the machine mechanically interacts with the body, the kinetic energy 2 / 2 0 Mvof some mass M moving at the velocity v 0 transforms into the work of bulk and shear viscous deformation of the powder body, which is accompanied by energy dissipation in the body and environment. The energy dissipation makes the process irreversible. A small portion of the energy is stored as strain hardening peculiar to viscous flow. The elastic stiffness and inertia of the system lead to damped oscillations. The higher the ratio of the elastic stiffness of the system to the viscous resistance of the deformable body, the more intensive is the damping of oscillations and the more energy goes to the irreversible deformation of the body. When this ratio is high, no damped oscillations occur and the dynamic process is aperiodically damped. This paper presents the results from computer simulation and analysis of experimental data on the densification of porous billets from copper and iron powders in α-and γ-phases in hot shock compaction [4]. The experiments were conducted in the South Russia Technical University (Novocherkassk, Rostov Region).At the early stage of the process (prior to irreversible deformation, i.e., before the deformable body reaches the elastic limit) the mechanical system behaves according to the classical second-order differential equation ( ) ( ) 0

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