Yield strength of tantalum for shockless compression to 18 GPa

Abstract

Effect of temperature, strain, and strain rate on the flow stress of aluminum under shock-wave compression J. Appl. Phys. 112, 073504 (2012); 10.1063/1.4755792Comparative studies of yield strength and elastic compressibility between nanocrystalline and bulk cobalt Modeling of the elastic precursor behavior and dynamic inelasticity of tantalum under ramp wave loading to 17 GPa A magnetic loading technique was used to study the strength of pure, annealed, and cold-rolled polycrystalline tantalum under planar ramp loading at strain rates of ϳ10 6 / s. Both the initial yield strength and the flow strength after compression to peak loading stresses of 18 GPa were determined. For sample thicknesses ranging from 0.5-6.0 mm, it was found that the elastic limit of ϳ3.2 GPa, corresponding to a yield strength of 1.6 GPa, for annealed Ta was sharply defined and essentially independent of sample thickness. After elastic yielding, relaxation of the longitudinal stress occurred for sample thicknesses greater than ϳ0.5 mm, approaching an asymptotic value of ϳ1.6 GPa. Two different purities of annealed Ta showed no difference in initial yield strength. Cold-rolling annealed Ta to 26% plastic strain resulted in a more dispersed elastic precursor with an amplitude of about 1.6 GPa and with no stress relaxation after yielding. Analysis of unloading wave profiles from the peak loading states allowed determination of the flow stress, which increased to about 0.9 GPa for annealed Ta and 1.3 GPa for cold-rolled Ta at peak stresses of 17-18 GPa.

Contrasting the effects of cold rolling on the shock response of typical face centred cubic and body centred cubic metals

“…In contrast, after a cold rolling treatment, no evidence of twining is observed (Figure 4a-b), although the microstructure has a significant number of long, low angle boundaries present. c) In a previous work [8] (also noted by others [7,9]) it was observed that the upper and low yield points at the HEL were removed by cold rolling. It was suggested that this was due to an accumulation of interstitial oxygen atoms around dislocations, effectively pinning them in place, and thus requiring a high stress to remove them.…”

“…For example, a reduction in stacking fault energy in fcc metals (either in a pure metal like silver [4], or via alloying in copper alloys [5]) can result in a shift in deformation mechanism from dislocation formation to twinning, whilst in bcc metals, a reduction in Peierls stress (such as in niobium) can result in a much higher proportion of the deformation being accommodated by dislocation generation rather than motion of pre-existing dislocations [6]. The effects of increasing dislocation density before shock loading has been much less studied, although a series of papers have reported on the role of dislocation density on tantalum [7][8][9]. In this paper, we examine the effects of dislocation density on the shock response of two near ideal fcc and bcc metals, copper and tantalum.…”

The spall strength and Hugoniot elastic limit of tantalum with various grain size

“…Tantalum has a high density (16.65 g/cm 3 ), melting temperature (2996 0 C) and is unique in it's combination of high hardness with high plasticity. Extensive research and publications are dedicated to investigations of the elastic-plastic properties and spall fracture of tantalum under shock-wave loading [5][6][7][8][9], but the question about the influence of structural factors on these processes remains unanswered.…”

Towards a final analysis of lateral gauge response

“…Ramp wave loading of annealed and cold worked tantalum has been carried out by Asay et al using magnetic induction techniques [11]. Their work is one of the few that allow direct comparison between independent strength measurements.…”

“…Histories for shocked tantalum are shown in Fig. 3 a) [11,12]. In annealed tantalum the stress rises to a precursor peak known as the isentropic elastic limit (IEL) by analogy with the Hugoniot Elastic Limit (HEL).…”