Viscosity of aluminum and lead in shockwave experiments

Abstract

Many engineering problems can be modeled within the framework of non-dissipative gasdynamic flows. However, some problems also involve large strains of various types of shells, and accounting for the elastoplastic properties of the materials becomes important if the characteristic pressures are too much greater than the yield point. By making such allowances, it is then possible to more accurately calculate the final strains and evaluate the heating of the shell due to dissipative forces. Also, dissipative losses due to viscous forces become important for high-speed flows characterized by high strain rates [1][2][3][4][5][6].Heating due to viscosity is usually characterized by large discontinuities in the dissipation of kinetic energy into heat. The greatest local heating is realized near various physical discontinuities in the material being deformed, i.e., near foreign inclusions and cavities, at grain boundaries and slip planes, etc. Nonuniform heating of the material due to viscosity will obviously lower its strength characteristics and can thereby facilitate deformation along certain planes and directions [6]. Typical examples of the latter are the piercing of a shell by a fragment or the deep penetration of a barrier by microscopic particles. Such penetration has recently been the subject of intensive research [7]. At the same time, these examples also serve to illustrate the present state of fracture mechanics, which has as yet been unable to quantitatively describe such experiments [8-101.It has long been known that dissipative processes are nontrivial in high-rate viscoplastic flows. For example, the authors of [1, 2] studied the dependence of the viscosity of several materials on compression and temperature behind a shock wave (compression range cr < 2, temperature T -104 ~ The viscoplastic properties of the materials were also studied in [3,11,12] in tests involving the inertial collision of cylindrical shells (compression a -1, temperature T -103 ~ The shells were accelerated and collided in these experiments as a result of energy supplied by an explosive. In this scheme, the parameters of the explosive charge and the shells can be chosen so that all of the initial kinetic energy of the shell is transformed into heat and the shells are left with a certain radius.It has been established that the main physical processes which occur in the shell material are characterized by nonuniform heating of the shell material through the thickness. The greatest degree of heating is reached on the internal boundary of the shell, and the degree of nonuniformity of the heating increases toward the shell's center [11,13]. This alters properties such as dynamic yield point and absolute viscosity.The phenomena mentioned above are likely to be seen to some extent in any high-rate viscoplastic flow. Progress in systematically accounting for dissipative losses during intensive viscoplastic flows in different problems involving high energy densities is being slowed by the lack of adequately developed phenomenological models ...

Dynamic viscosity and material relaxation time during shock loading

“…A comparison of the obtained results with the experimental-calculated data given in [10,16,[20][21][22] (see Table 2) shows satisfactory agreement [taking into account that formula (13) is approximate] among the calculated characteristics obtained for the proposed model (it should be noted that the author of the present paper is unaware of the structural parameters of materials for which data of [10,16,[20][21][22]) were obtained.…”

Measurements of the viscosity of iron and uranium under shock compression

“…Ogorodnikov et al [52] also approximated the data on the viscosity of aluminum and lead in the entire range of shock compression by relation (8) in which the activation energy was described by an analytical dependence in the form of a step function, which in fact corresponded to two significantly different values of effective activation energy in the region prior to and after melting under shock compression. These values were 2.1 and 56 kJ/mol for aluminum and 4.2 and 60 kJ/mol for lead.…”