Spall strength dependence on grain size and strain rate in tantalum
Published in Acta Materialia, 2018
Recommended citation: T.P.Remington, E.N. Hahn, S. Zhao (Corresponding author), R.Flanagan, J.C.E. Mertens, S. Sannagjoamrad, T.G. Langdon, C.E.Wehrenberg, B.R.Maddox, D.C.Swift, B.A.Remington, N.Chawla, M.A.Meyers. (2018). "Spall strength dependence on grain size and strain rate in tantalum." Acta Materialia. 158(313-329). http://sdlszst.github.io/files/Zhao_18_Acta Mater_Spall strength depends on grain size.pdf
We examine the effect of grain size on the dynamic failure of tantalum during laser shock and release and identify a significant effect of grain size on spall strength, which is opposite to the prediction of the Hall-Petch relationship because spall is primarily intergranular in both poly and nanocrystalline samples, thus, momocrystals have a higher spall strength than polycrystals, which, in turn, are stronger in tension than ultrafine grain sized specimens. Post-shock characterization reveals ductile failure which evolves by void nucleation, growth, and coalescence. Whereas in the monocrystal the voids grow in the interior, nucleation is both intra and intergranular in the poly and ultrafine grained crystals. The fact that spall is primarily intergranular in both poly and nanocrystalline samples is a strong evidence for higher growth rates of intergranular voids, which have a distinctly oblate spheroid shape in contrast with intragranular voids, which are more spherical. The length of geometrically necessary dislocations required to form a grain boundary void is lower than that of grain interior void with the same maximum diameter, thus the energy required is lower. Consistent with prior literature and theory we also identify an increase with spall experimental results and also predict grain boundary spearation in the spalling of polycrystals as well as an increase in spall strength with strain rate. An analytical model based on the kinetics of nucleation and growth of intra- and intergranular voids and extending the Curran-Seaman-Shockey theory is applied which shows the competition between the two processes for polycrystals
Recommended citation: T.P.Remington, E.N. Hahn, S. Zhao (Corresponding author), R.Flanagan, J.C.E. Mertens, S. Sannagjoamrad, T.G. Langdon, C.E.Wehrenberg, B.R.Maddox, D.C.Swift, B.A.Remington, N.Chawla, M.A.Meyers. (2018). “Spall strength dependence on grain size and strain rate in tantalum.” Acta Materialia. 158(313-329).