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This paper is a study on ricochet characteristics of metal plates hit by 25 mm APDS-T projectile. A series of ballistic tests has been carried out on three different armor steel types chosen to present a range of hardness. Each armor steel target was impacted at varying angles of incidence until ricochet was observed. This investigation is not only expected to help in understanding the phenomenon of projectile ricochet but also to provide some useful data that can be used for calibration and validation of the finite element (FE) models. In general, the ricochet angle was found to decrease with an increase in target hardness due to different failure mechanism.

The use of additive manufacturing (AM) by Electron Beam Melting (EBM) or Selective Laser Melting (SLM) has extensively grown in the past few years. A major goal in AM is to manufacture materials with mechanical properties at least as good as traditionally manufactured materials. In this work we present the results of planar impact tests and Split Hopkinson Pressure Bar tests (SHPB) on Ti-6Al-4V manufactured by EBM and LSM techniques. Stress strain curves based on SHPB measurements at strain rate of about 1500 s-1 display similar plastic flow stresses for SLM and EBM processed Ti-6Al-4V alloys, and about 15% higher than reported for commercial Ti-6Al-4V alloy. Results of planar impact tests on SLM samples display slightly higher spall strength than EBM while the stress at Hugoniot elastic limit (HEL) is practically the same. Hugoniot elastic limit and spall strength estimates for EBM-and SLM-processed Ti-6Al-4V alloys are at least as high as values obtained for conventionally-processed alloys. The results of post mortem SEM analysis of the spall fracture have demonstrated significant differences in the spall fracture characteristics between the AM-processed and commercial Ti-6Al-4V alloys.

The unique combination of SiC properties opens the ways for a wide range of SiC-based industrial applications. Dense silicon carbide bodies (3.18±0.01 g/cm 3 ) were obtained by an SPS treatment at 2050 °C for 10 min using a heating rate of 400 °C/min, under an applied pressure of 69 MPa. The microstructure consists of fine, equiaxed grains with an average grain size of 1.29±0.65 μm. TEM analysis showed the presence of nano-size particles at the grain boundaries and at the triple-junctions, formed mainly from the impurities present in the starting silicon carbide powder. The HRTEM examination revealed high angle and clean grain boundaries. The measured static mechanical properties ( H V =32 GPa, E =440 GPa, σ b =490 MPa and K C 6.8 MPa m 0.5 ) and the Hugoniot Elastic Limit (HEL=18 GPa) are higher than those of hot-pressed silicon carbide samples.

The high strain rate behavior of Spark Plasma Sintered (SPS) magnesium aluminate spinel (spinel) disc-shaped samples was studied under parallel (planar impact) and divergent (spherical impact) flow conditions. The results of planar impact experiments allowed determining the principal Hugoniot up to 40-GPa compressive stress. The Hugoniot Elastic Limit (HEL) ranged from 10.8 to 12.2 GPa and increases slightly with the magnitude of the impact. The spall strength determined in low-velocity impact experiments has a 0.63-GPa maximum at an impact stress of 1.7 GPa and vanishes completely as the impact stress exceeds 2.1 GPa. The spherical impact tests (convex copper impactors with radii of curvature from 45 to 550 mm and velocities from 290 to 570 m/s) were carried out in parallel with AUTODYN-2D numerical simulations of the experimentally recorded velocity histories. The results allowed establishing the compressive failure threshold surface of spinel in the principal stress space. At a transverse stress of 2.4 GPa, the failure threshold undergoes a change of the dominant mode of the inelastic deformation from brittle cracking to some form of ductile yielding.

The compressive failure threshold of boron carbide and silicon carbide ceramics has been studied in impact experiments with an axisymmetric divergent flow, generated by the impact of convex copper flyer plates having velocities in the 550–720 m/s range. The radius of curvature of the flyer plates was in the 88–650 mm range. The sample-window (sapphire) interface velocities or the velocities of the free surface of the nickel witness plate were monitored continuously by VISAR. The maximum shear stress achieved under different radial stresses, just prior to the sample failure, is associated with the compressive failure threshold of the ceramic. The compressive failure threshold of the studied ceramics and the parameters of their inelastic deformation were determined by matching the results of the AUTODYN-2D numerical simulation with the experimentally obtained waveforms. The compressive failure threshold of SiC is characterized by a transition from a brittle-like behavior below a radial stress of about 1.5 GPa, to a ductile-like one at higher radial stresses. Boron carbide, in contrast, displays an apparently brittle failure over the whole studied stress interval.

The spall strength of silicon carbide (SiC) and boron carbide (B4C) ceramics processed by Spark Plasma Sintering (SPS) has been studied as a function of the loading stress. In the course of the planar impact experiments, the velocity of either the sample free surface or of the sample–window interface was continuously monitored by a Velocity Interferometer System for Any Reflector (VISAR). With the increase of impact stress the spall strength of both ceramics, increases initially and then declines monotonously until it vanishes almost completely, as the impact stress approaches the respective Hugoniot Elasic Limit (HEL). The mechanisms that may account for that behavior and, in particular, the role of the compressive wing cracks in the onset of the spall strength decline are discussed.

Spark plasma sintering (SPS) has become a popular technique for the densification of covalent ceramics. The present investigation is focused on the static mechanical properties and dynamic compressive behavior of SPS consolidated boron carbide powder without any sintering additives. Fully dense boron carbide bodies were obtained by a short high temperature SPS treatment. The mechanical properties of the SPS-processed material, namely hardness (32 GPa), Young modulus (470 GPa), fracture toughness KC (3.9–4.9 MPa m0.5), flexural strength (430 MPa) and Hugoniot elastic limit (17–19 GPa) are close or even better than those of hot-pressed boron carbide.

In this paper we discuss three different experimental configurations to diagnosing the modes of inelastic deformation and to evaluating the failure thresholds at shock compression of hard brittle solids. One of the manifestations of brittle material response is the failure wave phenomenon, which has been previously observed in shock-compressed glasses. However, based on the measurements from our “theory critical” experiments, both alumina and boron carbide did not exhibit this phenomenon. In experiments with free and pre-stressed ceramics, while the Hugoniot elastic limit (HEL) in high-density B 4 C ceramic was found to be very sensitive to the transverse stress, it was found relatively less sensitive in Al 2 O 3 , implying brittle response of the boron carbide and ductile behavior of alumina. To further investigate the effects of stress states on the shock response of brittle materials, a “divergent flow or spherical shock wave” based plate impact experimental technique was employed to vary the ratio of longitudinal and transversal stresses and to probe conditions for compressive fracture thresholds. Two different experimental approaches were considered to generate both longitudinal and shear waves in the target through the impact of convex flyer plates. In the ceramic target plates, the shear wave separates a region of highly divergent flow behind the decaying spherical longitudinal shock wave and a region of low-divergent flow. Experiments with divergent shock loading of alumina and boron carbide ceramic plates coupled with computer simulations demonstrated the validity of these experimental approaches to develop a better understanding of fracture phenomena.

Compressive failure strength of brittle solids increases rapidly with the confining pressure whereas the yield stress of ductile materials is much less sensitive to the confinement. The presented experimental technique utilizes this difference in the effect of the confinement in order to reveal the mode of ceramics behavior under shock-wave compression. A controlled confining pressure on the lateral surface of the disk-like ceramic specimen was produced by fixing the specimen into a shrink-fit metal sleeve. The effect of such confinement on the Hugoniot Elastic Limit should differ by a factor of about 2 5 for the materials whose ductile yielding is governed by Von Mises criterion and those obeyed the Griffith's criterion of brittle failure. Results of the tests performed exhibit unambiguously the ductile response of the alumina ceramics whereas the response of the boron carbide ceramics is certainly brittle.

Planar impact experiments widely used for determining dynamic strength of hard materials do not provide a possibility to obtain information about the mode, ductile or brittle, of their inelastic response or about thresholds conditions of their compressive failure. Using the controlled sample pre-stressing in the experiments (E. Zaretsky and G. Kanel, APL, 2002, 81, 119) allows one only to conclude whether the response of the studied material at the stress level of elastic limit is brittle or ductile leaving the problem of the material compressive failure threshold still unsolved. The experimental/numerical technique for determination of compression failure threshold of brittle solids is presently suggested. The technique is based on measuring the velocity of the sample/window interface while the sample front surface is struck by curved copper impactor. The divergent stress flow produced by such loading results in the incipient compressive failure of the sample and, respectively, in the appearance of the failure signatures at the measured velocity profile. Reproducing these signatures with aid of AUTODYN 2D commercial computer code including the constitutive and failure description of the studied material yields the values of the principal stress tensor components corresponding to the brittle failure initiation. The locus of these values in the principal stress space is the material compressive failure surface.

Axisymmetric divergent flow characterized by increasing (with propagation distance) difference between longitudinal and radial stress was produced in the plane‐parallel alumina samples by impact of spherical (R=200–600 mm) copper impactors having velocities 210 to 260 m/s. The velocity of the interface between the impacted 5‐mm alumina samples and 6‐mm sapphire windows was continuously monitored by VISAR. Preliminary AUTODYN simulations show that such impact is capable of producing in the sample the stress states which cannot be produced by planar impact loading and which may result in the brittle failure of alumina. Actually, the waveforms recorded in these experiments contain distinct signatures of the alumina failure. AUTODYN numerical simulations of the experiments allow one finding the alumina failure threshold, the path of the increasingly damaged alumina, the kinetics of this damaging and the locus of the states of comminuted material in the principal stress space. Possible applications of the deve...

The presented experimental technique uses a radial sample pre‐stressing in order to reveal whether the behavior of ceramics is brittle or ductile under uniaxial shock‐wave compression. The controlled radial pre‐stressing of ceramic samples was produced by a shrink‐fit steel sleeve. The HEL increment caused by the pre‐stressing was expected to be of about 2.5 times higher for materials whose brittle failure in compression is governed by Griffith’s criterion than for those that obeyed the Von Mises criterion of ductile yielding. The experiments indicate certainly ductile behavior of hot‐pressed alumina samples whereas the samples of hot‐pressed high‐density (2.5 g/cm3) boron carbide exhibit compressive failure. The lateral pre‐stressing of boron carbide samples of lower density (2.37 g/cm3) results in a slight HEL decrease that is treated in terms of a compaction process.