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Strain-Rate Sensitivity of Nanocrystalline Cu–10Ta to 700,000/s

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Several miniature Kolsky bars are used to obtain stress–strain curves for nanocrystalline Cu–10Ta over a range of high strain-rates. The smallest bar (steel) has a 305 μm diameter, and achieved rates up to 700 × 103/s. Different sample sizes are needed to obtain different strain-rates, and it is shown that there is no appreciable sample size effect when different sizes are tested at similar strain-rates, even though the sample sizes vary by over an order of magnitude. No significant increase in strain-rate sensitivity is noted over the strain-rate range studied, i.e., the strength increases linearly with the logarithm of strain-rate from 0.001/s to 700 × 103/s.

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    The exact theory assumes an infinitely long bar, but is assumed to apply to the free-end measurements made here. However there does not seem to be much error at least up to 7.5 MHz.

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    This is not due to any equilibrium problems in the sample, which may also be the case, i.e., a stress–strain curve may not be valid for low strains due to the need for the sample to “ring-up” to an adequate state of equilibrium.

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    Note the use of a low-impedance striker results in it rebounding back into the barrel—this may pose a hazard in some gun systems.


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Casem, D., Ligda, J., Walter, T. et al. Strain-Rate Sensitivity of Nanocrystalline Cu–10Ta to 700,000/s. J. dynamic behavior mater. 6, 24–33 (2020). https://doi.org/10.1007/s40870-019-00223-w

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  • High Rate Testing
  • Kolsky Bar
  • Metal Plasticity