The purpose of this work is to show that the spherical shock waves arising in a liquid during cavitation bubble collapse can lead to formation of deep needle-like pits on the solid surface. The nature of dynamic damage during cavitation erosion is the spallation caused by interference of rarefaction waves. Rarefaction at spherical wave impact arises when the velocity of contact surface boundary becomes less than the speed of sound in a target. If the tension caused by the focused rarefaction wave exceeds the spall strength of material, channel spall cracks can arise. At low pulsed loading, spall cracks are formed in a dynamic fatigue mode. Needle-like damage arises upon focusing rarefaction waves. In terms of our model, a system of cylindrical spall cracks is consecutively formed around a deeper axial spall needle-like crack. Upon subsequent loading, each crack acts as a source of new rarefaction wave. Newly formed cylindrical spall cracks suppress the growth of the cracks of previous generation and give birth to the cracks of next generation. A distinctive feature is that the cracks are first formed at the periphery of damageability zone, subsequent cracks having a lower depth.

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The ranges of solid-state detonation velocities are estimated, based on the volume velocity of sound in the reacting mixture (lower limit) and the wave velocity corresponding to the pressure of polymorphic transformation of the product with formation of a more dense phase (upper limit). The latter values are consistent with gas-dynamic estimates of detonation velocities and correlate with detonation velocities of typical high explosives.Key words: solid-state detonation, shock adiabats of mixtures. Bennett and Horie [1] and Gordopolov et al. [2]predicted the emergence of detonation as a result of a condensed-phase synthesis reaction in the shock-wave regime with heat release and an increase in system volume. Guriev et al. [3] succeeded in obtaining solidstate detonation (SSD) in a reacting mixture of powdered Zn + S with a mean velocity of 2.2 ± 0.2 km/sec on the base of 200 mm. This result was determined by particular test conditions: particle size, porosity, sample diameter, and intensity of the initiating shock wave. It seems of interest to estimate the theoretical limits of SSD velocity in a monolithic medium (D 0 ) with an ideal formulation of the experiment. The substances used in the study were Be, Zn, and Cd chalcogenides crystallized in the B3 structure. Formation of these chalcogenides from the mixtures of components is accompanied by release of a large amount of heat and by an increase in volume at standard or slightly elevated pressures (ZnS).By definition, detonation is a supersonic process; hence, the minimum SSD velocity has to be greater than the volume velocity of sound in the initial mixture, i.e., the coefficient a in the Hugoniot equation D = a + bU.(1)The shock adiabats of the mixtures were calculated on the basis of the additivity principle with the use of