I. V. Simonov

Mechanics of dynamic penetration into soil medium

This paper presents a survey of the results of experimental and theoretical studies in the field of high-speed penetration into soil media, which were obtained in the Institute for Problems in Mechanics, Russian Academy of Sciences. New methods for determining the dynamic parameters of such media are proposed. The laws of trajectory refraction and ricochet in oblique penetration of a single body or a group of bodies into an elastoplastic medium are studies and the phenomenon of partial ricochet is described. The results of numerous experiments were used to discover the possibilities for controlling the process of cavity formation. The specific characteristics of penetration into a statically or dynamically perturbed medium were investigated. A series of experimental studies were performed to compare the penetration of axially symmetric and equivalent spatial (starshaped) bodies. The theoretical background was based on the principle of locality in the approximate description of the contact body-medium interaction, in which the problem of the body motion by inertia in a medium is reduced to the problem of the dynamics of a rigid elongated body with flow separation. The trajectories of curvilinear motions of bodied in an elastoplastic medium are modeled and classified by calibrating and testing the model in nontrivial experiments. Several criteria for stability of elongated body rectilinearmotion on infinite time intervals are formulated; as calculations showed, these criteria ensure the practical stability in the case of deep penetration.

Prediction of arbitrary crack growth from the interface between two dissimilar elastic materials

Based on the universal laws of stress distribution around a crack edge, the general analysis of crack start from the interface is given. The solution for the original crack is assumed to be known. In order to classify different possible cases of crack growth beginning, both a slip-region ahead of the opening zone and a core region near the crack edge are introduced. The former provides non-overlapping of the crack surfaces and removes an undesirable oscillating stress field singularity which is produced mathematically at the assumption of a completely opening crack. The latter means that we consider the damage of an elementary volume (geometrical measure of the microstructure) as a discrete fracture operaton. Two asymptotical cases are studied: the slip-region is much smaller or much larger than the cross-section of the core region. Then the stress-strain state on the core region periphery qualitatively is the same as for a completely opening or shear interface crack, respectively. A characteristic crack opening appears instead of a characteristic length of the slip-region for a blunted crack. The angles of crack departure are predicted according to different known criteria of fracture. In passing, parametric, analysis of stresses and energy density angle distributions are given. Plane and penny-shaped cracks are examined as the illustration.

On the jet collision: General model and reduction to the Mie-Grüneisen state equation

We study the stationary direct supersonic collision of jets of condensed materials. We determine the basic flow characteristics: the maximum values of pressure, temperature, and densities on outgoing shock wave fronts and at the wave stagnation and penetration points. To this end, just as in the Lavrentiev problem about the jet collision in the framework of an incompressible fluid model, it suffices to consider the flow only along the central streamline, i.e., the symmetry axis. We consider the general caloric (incomplete) equation of state and, to close the thermodynamic construction and determine the temperature dependence on the state parameters, supplement them with thermodynamic identities. We also consider the conditions on discontinuities, the Bernoulli integrals, i.e., the conservation laws, to relate the states behind the wave front and the stagnation point, and the continuity conditions at this point. Just as in the collision problem for jets of incompressible fluid, we neglect the strength, viscosity, and heat conduction. As a result, we construct a mathematical model, i.e., a system of 12 integro-algebraic equations, and propose a semi-inverse solution method, in which the system splits into separate equations. In the special case of the Mie-Grüneisen state equation, the system becomes much simpler. We perform computations and construct the dependence of maximal pressures and temperatures on the impact velocity in the range 1–20 km/s for many pairs of materials of the colliding jets. We also compare the results with the solution obtained according to the incompressible fluid model.

The feasibility of using large impact to destroy a dangerous asteroid

Abstract Some physical aspects of high velocity ( >30 km / s ) collisions involving an asteroid or comet nucleus are discussed. Impacts by both meteoroids and massive artificial objects are considered; these may result in effects such as gas expansion reaction forces, shock wave propagation, and fragmentation. The approach is based on conservation laws and observed phenomena associated with high energy impacts, combining data on the attenuation of strong and weak shock waves in rocks and data on the strength of meteorites as determined by their observed breakups in the atmosphere. The calculations accept the prevailing view that asteroids are structurally inhomogeneous and contain some initial crack distribution, possibly of the type that has been observed in meteorites. Analytical estimates for the mean fragment size distribution and the volume of a fragmentation zone are derived from a step-by-step analysis of the wave evolution. This leads to the surprising conclusion that a powerful impact can cause the complete disruption into small pieces of a much larger monolithic asteroid (1– 2 km in diameter—by an impact with a kinetic energy of less than 1 Mt ) than previously thought. In particular, an artificial very massive projectile might be assembled from low-orbit space debris (dead satellites, abandoned space stations, etc.). This suggests that kinetic energy impacts are a viable alternative to nuclear explosions, which other authors have concluded as that required to protect the Earth from an asteroid on a collision course. Recent experimental and theoretical results are also used to compare the total change of asteroid momentum due to a high energy impact to the momentum produced by gas expansion, and also to that resulting from a nuclear explosion.

Possibilities for hypervelocity impact experiments in frames of demonstration project “Space Patrol”

It is proposed to reach impact velocity of macrobodies up to 90 km/s by collision of space probe with celestial bodies in meteor flux. Results of the approach dynamics and targeting simulation shows feasibility of this idea. Science experiments and registration method, based on measuring electromagnetic fields, inducing during the impact, are proposed. It is shown, on the basis of an impact experiment of the small mass body, that it is possible to determine parameters of asteroids such as dynamic strength, crack resistance etc.

Elastodynamic well-defined fields around a propagating interface open-crack edge

The general non-trivial asymptotic structure of stress/displacement fields around a small domain adjacent to a propagating interface crack edge and containing a small width slip-region is described in ordinary functions. The method of determining such kind of the boundary layer bases upon the asymptotic expansion matching method, complex potentials, and conform mapping. For this purpose an in-plane singular problem in the theory of linear elasticity is formulated for two dissimilar transversely-isotropic interacting half plane. The sought-for solution as the first-term of an inner expansion matches the oscillating singularity given in a general view which is the first-term of an outer expansion in, may be, general 3-D completely-open-crack problem. The unilateral constraints and unknown boundary of the slip-zone are the additional new features of the problem. The finding refine physically untrue solutions within small strip-type, near-crack-path domains in simpler interface open crack problems. A propagating semi-infinite cut with the alternative contact conditions and the penny-shaped stationary crack are considered as examples of a dynamic case and a curved crack-path. The accuracy of the approach is shown by comparing with a strict solution.

Experimental studies of crack dynamics in polymer films

Using high-speed video recording, we observed fast propagation of cracks across polymer film strips of different rheology and determined several quantitative characteristics of their motion. We discovered and described a series of characteristics of the crack path variation, the dynamical behavior of the adhesion zone ahead of the crack, and its branching before coming out to the free surface.One of the most important mechanical problems is to construct models of fracture of materials and structural elements. The goal of experimental studies of crack propagation is to classify thesemodels. Slow crack growth in thin films has been considered in many papers. For example, in the recent paper [1], subcritical crack growth in polycarbonate films under the action of tensile loads less than limit loads was studied in the case where the adhesion zone length is comparable with the crack length. However, the authors are not acquainted with any studies of fast crack propagation in films. In the present paper, we generalize the results of processing of experimental data in fast processes of fracture of polymer film strips of two types. Examining high-speed video recording frames, we studied the laws of propagation of a crack from the initial cut in a film made of hard polyester and laws of development of the crack tip zone in a film made of soft polypropylene admitting large plastic strains. We determined the rate of defect growth in time. We observed the formation of qualitatively different plastic regions near the crack tips in films of different thickness and rheology and described scenarios of crack coming out to the free surface. We discovered the effect of branching of a narrow and long plastic tip zone as the crack approaches the free boundary leading to putting out a small triangular piece of the film.

Electromagnetic Radiation Method for Identification of Multi-Scale Fracture

The electromagnetic radiation (EMR) as well as acoustic emission (AE) is the statistical phenomenon in fracture. Measurements of EMR can serve the purpose of identification. The experimental data on this point are known for ion crystals, metals, rocks. The explanation of physical mechanism has been given ideally, for example, in the case of shock wave in an “ideal” metal.