This paper presents the results of metallographic analysis of the melting of S1 lead under shock-wave loading and unloading. Lead samples in a titanium capsule were loaded by a plane shock wave using an aluminum impactor 6 mm thick, which was accelerated by detonation products of an explosive. The results of metallographic analysis of samples in the initial state, subjected to heat treatment under normal conditions, and recovered after shock-wave loading are given. Melting traces were found in lead after shock-wave loading by a pressure of 25.6 GPa and subsequent unloading.

The authors present results of sound velocity measurement in shock-compressed samples of VT1-0 titanium and VT-20. The measurements were accomplished by the rarefaction overtake technique with use of indicator liquids and by the reverse impact method with use of laser interferometer. In titanium, kinks were recorded at the dependence of sound velocity on pressure at the pressures of 20–40 and 60–90 GPa. These kinks can be explained by phase transitions. X-ray structural analysis revealed presence of the ω-phase in the samples, which had been recovered after loading by pressures in steel ampoules in the range from 9 to 23 GPa. Beginning of VT-20 alloy melting relates to pressure of 130 GPa at shock adiabat.

We present investigations of beryllium spall fracture with samples of dimensions circle divide 65x7 mm, which were made via vacuum hot pressing. Samples were loaded at normal incidence by a detonation wave of the explosive charge of TG 5/5 composition, 7, 14 and 30 mm in thickness, which gave shockwave stresses of 21-25 GPa within the sample. Spall fractures formed as the sample unloading at an air gap. A velocity profile was measured at the free boundary using VISAR laser interferometer, a spall layer thickness was measured with two-frame impulse X-ray radiography, and the shockwave profile was measured via a manganin-based gauge in a fluoroplastic base in the course of deceleration of a spall layer and of a basic part of beryllium. Hugoniot dynamic yield strength (Y-HE) and spall strength (sigma(p)) were measure as 0.69-0.73 GPa and 0.85 +/- 0.03 GPa, respectively, at a strain rate of epsilon similar to 10(4) s(-1) in the unloading part of the incident pulse. A weak dependence between the spall layer thickness and HE layer thickness was recorded in tests. The weak dependence is not described through existing damage models and points to the need to develop more sophisticated models.

The effect of the initial microstructure and microstructure obtained after quasi-isentropic and shock compression on the elastic-plastic and strength characteristics of grade M1 copper upon static, quasistatic, and dynamic loading has been investigated. It has been revealed that the parameters of a shock wave play an important role in the formation of the substructure and related mechanical properties of the samples and that the values of the elastic-plastic and strength characteristics in coarse-crystalline samples of copper M1 vary substantially depending on the defect structure at the identical grain size. Measurements of the elastic limit and critical fracture stresses over a wide range of the loading durations have been performed by different methods, including a VISAR laser interferometer. Based on the experimental data obtained, models of the shear and spall strength of copper for different loading conditions have been developed. With the aid of a NAG two-stage kinetic model, a numerical simulation of the dynamic fracture of coarse-crystalline samples of copper M1 with different internal structure has been performed. An analysis of the experiments in combination with the numerical simulation made it possible to describe the deformation behavior of the samples in the entire range of loading rates.

The nucleation and evolution of damage in annealed coarsely crystalline M1-type copper subjected to fast loading to a pressure P ∼ 32 GPa, followed by the action of tensile stresses σ p with an intensity of ≈−2.0 GPa for a time t ≈ 0.3–1.5 μs, have been investigated numerically and experimentally. It has been shown that, at a specific combination of amplitude-time characteristics of the tensile stress pulse, damage localization in some cases at t < 1 μs has been observed in zones (∼10–14 mm in size) alternating with “dead” zones (∼3–5 mm in size) containing no visible damages. Pores are connected by “yield streamlets.” The existing multistage models of fracture kinetics have neither explained nor predicted the formation of a “band” damage structure or the presence of “yield streamlets” in specimens.

It is shown that preloading of fine-grained copper with a the grain size of 0.5 m by a shock wave of intensity ≈25–50 GPa does not lead to changes in its internal microstructure and mechanical properties, and the dislocation density increases only slightly from 1.8 · 1011 cms-2 in the initial state to (3.1–3.6) · 1011 cms-2 after shockwave loading. An increase in shock wave intensity to pressures > 55 GPa leads to a decrease in the dislocation density to 2.5 · 109 cms-2, an increase in the grain size to ≈19 fum, the occurrence of microtwins inside the grains, and a reduction in the mechanical properties of fine-grained copper to the level of coarse-crystalline copper.

The paper presents results of experimental researches on spall fracture of polycrystalline copper when loading by shock waves with intensity of 20–33 GPa and duration < 1 μs. It is shown that decrease of copper spall strength is observed behind SW front at SW intensity of ∼ 33 GPa (above threshold of formation of heterogeneous deformation bands). When reducing SW intensity to 27 GPa, spall strength is restored. Duration of the softened copper state does not exceed ∼ 0.5 μs. The method for spall strength evaluation is based on measurement of maximum damage in post-test samples.

Metals subjected to compressive shock of sufficient intensity often undergo microstructural changes involving deformation localization and temporal softening. Temporal softening has a significant effect on the formation of damage (the material is much more susceptible to damage during the period of temporal softening). The present on polycrystalline M1 copper clearly exhibits this phenomenon.

Temporal softening that is associated with the passage of a shock wave is investigated along with its effect upon material strength and issues of macroscopic scaling. Specimens are loaded in such a way that a moderate tensile pulse is applied during the temporal window of softening. It is found that strength is reduced as a consequence of temporal softening. It appears that temporal softening contributes to a reversal of typically observed macroscopic scaling effects.