Shear strength of shock-loaded polycrystalline tungsten

Abstract

Previous experiments have suggested that tungsten undergoes a significant loss of shear strength when shock loaded to stresses greater than 7 GPa. In order to investigate this effect in more detail, a series of experiments was conducted in which polycrystalline tungsten was first shock loaded to approximately 10 GPa and then either unloaded or reloaded from the shocked state. Analysis of measured time-resolved wave profiles indicates that during initial compression to 9.7 GPa, the shear stress in polycrystalline tungsten increases to a maximum value of 1.1 GPA near a longitudinal stress of 5 GPa, but decreases to a final value of 0.8 GPa for stresses approaching 10 GPa. During reloading from a longitudinal stress of 9.7 GPa to a final value of ∼14 GPa, the shear stress increases to a peak value of 1.2 GPa and softens to 1.0 GPa in the final state. During unloading from the shocked state, the initial response is elastic with a strong Baushinger effect. Examination of a recovered sample shows evidence for both deformation slipping and twinning, which may be responsible for the observed softening.

Deformation of a Low-Cost Ti-6A1-4V Armor Alloy Under Shock Loading

“…For 3.4 Re-Shock Experiments. The re-shock experiment (Asay et al 1980) uses a twomaterial target, as shown in the sample configuration of Figure 12. A second higher impedancetarget is mounted against the rear of the primary target material.…”

Shock Response of a Heavy Tungsten Alloy

“…The error associated with the values of density at the HEL is 4% . Elastic precursors in polycrystalline tungsten (Asay et al, 1980) and in an annealed tungsten alloy of a similar composition alloy such as 93W (Baoping et al, 1994) showed similar dispersions. Baoping et al (1994) found that the free surface velocities corresponding to HEL decreased from 0.072 km/s in a specimen of thickness 1.88 mm to 0.044 km/s in a specimen of thickness 11.68 mm.…”

“…The direct impact experiments provided information about the shock compressed state and release therefrom in this alloy without requiring any information about its physical or mechanical properties. Asay et al (1980), and Gaeta and Dandekar (1988) gave details of the conventional transmission experiments and direct impact experiments.…”

“…Since the deformation of 93W above its HEL proceeds plastically, an estimate can be made of the magnitude of shear stress sustained by the alloy and associated longitudinal plastic strain induced in it as a function of impact stress. Such an estimation can be done in three ways (Asay et al, 1980): (i) by comparison of longitudinal stress states with hydrostatic response, (ii) by differential relation for shear stress, and (iii) by self-consistent determination of shear stress. Since neither the hydrostatic response nor experimental results pertaining to the third method are available for 93W at the present time, the second method of the estimation is adopted for calculating the magnitude of shear stress and strain under shock compression.…”

“…Under tension it is measured by the magnitude of spall threshold. This work was undertaken to determine both of these properties of a tungsten alloy containing W, Ni, and Fe in the ratio of 92.85:4.9:2.25 by weight under shock loading condition, compared with those of pure polycrystalline tungsten (Dandekar, 1976;Asay et al, 1980;Zurek and Gray III, 1991), and other heavy tungsten alloys, annealed 93W (Baoping et al, 1994), 90 W-7 Ni-3 Fe (Hauver, 1980;Zurek and Gray III, 1991;Chang and Choi, 1998) and Kennertium Grade W-2 consisting of tungsten, nickel, iron, copper, and cobalt (Gaeta and Dandekar, 1988).…”