Additively Manufactured (AM) materials have great potential for producing graded materials, embedded structures and near net complex shapes. AM maraging steel properties have been compared with wrought maraging steel. The comparison featured interrupted tensile tests over a range of temperatures and strain rates. In addition a specially designed Tensile Split Hopkinson Pressure Bar (TSHPB) has been built to test very high strength metals at high strain rates. The results showed that the AM maraging steel was much more ductile than expected and exhibited significant necking under all conditions tested. All the samples exhibited ductile fracture. Although not as ductile as the wrought material, the AM material could be cost effective through economies of scale for complex components. The microstructure contained inclusions which derived from either the powder or the AM process and thus there is significant potential to improve these materials further. A modified Armstrong-Zerilli model was also constructed for these materials and shown to predict the raw experimental data within experimental error using DYNA3D simulations.
Space penetrators are a potential method of inserting instrumentation onto ice-covered bodies in the solar system. Part of a study to see whether this is feasible involves numerically simulating impact of the penetrator into ice at impact velocities of a few 100 m/s. In order to do this accurately, it is necessary to have a constitutive model for water ice that is valid at the strain rates and temperatures relevant to impact in the Outer Solar System. This paper reports certain issues and difficulties that arose during a study to obtain this data.
Static triaxial cell data and Split Hopkinson Bar data has been generated for well controlled dry and wet sand under confined and unconfined conditions. This has demonstrated that the dry sand is rate independent in its behaviour, whereas the wet sand exhibits a strain rate dependency in its behaviour. Simulations have been performed with the Lagrangian hydrocode DYNA using a Porter-Gould equation of state (EOS) and Johnson-Holmquist type constitutive model. Comparison with the raw strain gauge data is qualitatively reasonable, although some of the details of the trace are not reproduced. Sensitivity studies have also been performed, which has demonstrated some deficiencies in the constitutive model, relating to wave-speed and definition of moduli in a granular material. This has given some insights into how the constitutive model should be improved and which future experimental tests will be required.
Full-scale ballistic experiments using tungsten rods and rolled homogeneous armour (RHA)
steel plates are expensive to perform. For this reason, a study has been performed into
the possibility of using less expensive, more easily available metals in small-scale laboratory
experiments. The metal pairs chosen listed in order as armour/penetrator materials were:
RHA steel/tungsten, dural/mild steel, and copper/aluminium. In order to be able to use as
many diagnostics as possible (including high speed photography, VISAR, stress gauges) the
reverse ballistic configuration was used. This configuration also allowed the determination
of the high rate, low strain mechanical properties of mild steel to be determined. Finally,
a comparison was made between experiment and numerical predictions made using a mod-
ified Armstrong-Zerilli constitutive model for the RHA steel/tungsten pair. The model was
found to underpredict the penetration, probably because failure mechanisms were not incor-
porated.
As part of an effort to improve the general understanding of ductile granular materials under shock wave loading we have performed a number of experiments to test their behaviour dur- ing an impact experiment. In particular, we have obtained wave profiles and determined the princi- ple Hugoniot for 14% porous Aluminum in the stress range of 0.6-4.6 GPa. The Hugoniot data compare reasonably well with a Mie-Gruneisen equation of state. However, the wave profiles ex- hibit structure that suggests a relatively high yield strength and large dispersive properties, structure that a purely thermodynamic EOS cannot explain. The wave profiles themselves have been com- pared with numerical simulations using GRIM, the two-dimensional Eulerian hydrocode, and show relatively good agreement.
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