New data on the kinetics and governing factors of the spall fracture of metals

This paper presents two examples of significant departures from usual trends of varying the resistance to spall fracture (spall strength) with changing loading history, load duration and peak shock stress. In experiments with vanadium single crystals we observed an important decrease of spall strength when increasing the shock stress. This was interpreted in terms of disruption of the matter homogeneity as a result of its twinning at shock compression. In experiments with 12Kh18N10T austenitic stainless steel we observed a sharp increase of recorded spall strength value when short load pulses of a triangular profile were replaced by shock pulses of long duration having a trapezoidal shape. This anomaly is associated with formation of the deformation-induced martensitic phase

Peculiarities of evolutions of elastic-plastic shock compression waves in different materials

In the paper, we discuss such unexpected features in the wave evolution in solids as strongly nonlinear uniaxial elastic compression in a picosecond time range, a departure from self-similar development of the wave process which is accompanied with apparent sub-sonic wave propagation, changes of shape of elastic precursor wave as a result of variations in the material structure and the temperature, unexpected peculiarities of reflection of elastic-plastic waves from free surface

Effect of small preliminary deformation on the evolution of elastoplastic waves of shock compression in annealed VT1-0 titanium

The evolution of an elastoplastic waves of shock compression in VT1-0 titanium in the as-annealed state and after preliminary compression is measured. A preliminary strain of 0.6% and the related increase in the dislocation density are found to change the deformation kinetics radically and to decrease the Hugoniot elastic limit. An increase in the preliminary strain from 0.6% to 5.2% only weakly changes the Hugoniot elastic limit and the compression rate in the plastic shock wave. The measurement results are used to plot the strain rate versus the stress at the initial stage of high-rate deformation, and the experimental results are interpreted in terms of dislocation dynamics

Quasi-static and shock-wave loading of ultrafine-grained aluminum: effect of microstructural characteristics

The interrelation between microstructural characteristics and mechanical properties under quasi-static and shock-wave (dynamic) loading was investigated in ultrafine-grained aluminum processed by accumulative roll bonding (ARB) for 4, 7, 10 and 14 cycles. The microstructural parameters such as the size of the elements of grain–subgrain structure, grain size and fraction of high-angle grain boundaries were obtained using transmission electron microscopy (TEM) and electron back scatter diffraction (EBSD). Indentation and tensile tests at the strain rate of 1 × 10−4 s−1 were applied as the quasi-static loading, the impact by aluminum flyer-plates with the impact velocity of 620 ± 30 m s−1 was the shock-wave loading. The strain rate in the rarefaction wave before spall fracture was 2 × 105–7 × 105 s−1 in the latter case. It is shown that the dislocation substructures and low-angle subboundaries significantly affect the strength properties under quasi-static conditions, while the grain size (the areas bounded by only high-angle boundaries) and fraction of high-angle grain boundaries mainly define the dynamic strength properties. The different influence of the microstructural characteristics on the quasi-static and dynamic mechanical properties is related to the easier dislocation cross-slip under high strain rates

Method of measurement of the dynamic strength of concrete under explosive loading

Within the framework of the search for the method of determination of the strength properties of concrete under the action of an explosion or high-velocity impact, suitable for large scale concrete samples, the evolution of the compression pulse in plates or rods made of concrete with compressive strength of 30 MPa was investigated. It was found that wave configuration consisting of the ramped elastic precursor with insignificant stress jump at the front followed by a dispersed plastic shock wave is formed in the plates under uniaxial shock compression. In this experimental configuration, the compressive strength of the material is not identified. Experiments with concrete rods of various diameters have demonstrated the scalability of the wave process. It was established that the compressive fracture of the rods occurs at a distance of around twice their diameters and is accompanied by the fast decay of the load pulse after that weakly decaying elastic wave was propagated along the rods. The measurements of parameters of the compression pulse at the end of the fracture zone allowed us to determine the value of the dynamic compression strength of concrete equal to 105±20 MPa , which turned out to be 3.5 times higher than the static strength