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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.

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.