Resistance to dynamic deformation and fracture of tantalum with different grain and defect structures

Abstract

This paper presents the results of measurements of the strength properties of technically pure tan talum under shock wave loading. It has been found that a decrease in the grain size under severe plastic defor mation leads to an increase in the hardness of the material by approximately 25%, but the experimentally measured values of the dynamic yield stress for the fine grained material prove to be less than those of the ini tial coarse grained specimens. This effect has been explained by a higher rate of stress relaxation in the fine grained material. The hardening of tantalum under shock wave loading at a pressure in the range 40-100 GPa leads to a further increase in the rate of stress relaxation, a decrease in the dynamic yield stress, and the dis appearance of the difference between its values for the coarse grained and fine grained materials. The spall strength of tantalum increases by approximately 5% with a decrease in the grain size and remains unchanged after the shock wave loading. The maximum fracture stresses are observed in tantalum single crystals.

Transition of mechanisms underlying the rate effects and its significance

“…However, it is only enlarged by 38.88% when the strain rate grows from 10 3 to 10 9 s À1 . This sharp increase of e f after a specific strain rate observed in simulations is very similar to that in experiments [10]. Since no additional velocity rescaling is imposed on the atomic system, the statistic temperature varies during loadings.…”

“…Various mechanisms were introduced to explain the relationship at different strain rate range. For example, it is generally known that for many metals, the dependence of flow stress sharply increases when the strain rate of deformation exceeds about 10 3 -10 4 s À1 which is interpreted as the consequence of the change in mechanism [10]. Mechanisms such as dislocation generation, deformation twinning, and adiabatic shear banding were proposed to explain the dependency [11,12].…”

Dynamic behavior of zirconium alloy E110 under submicrosecond shock-wave loading

“…3. Similar to previous studies [6][7][8][9][14][15][16], attenuation measurement results are approximated by the following empirical relation: Figure 3. Relationships of measured dynamic elastic limit σ h , yield strength σ τ , calculated plastic train rate γ p , and measured strain rate behind the elastic precursor front where S = 0 .87 GPa, α = 0 .138 , and h 0 = 1 mm.…”

“…3. Similar to previous studies [6][7][8][9][14][15][16], attenuation measurement results are approximated by the following empirical relation:…”

Deformation of zirconium – niobium alloy E635 in sub-microsecond shock waves

“…Analysis of elastic precursor attenuation provides information on the initial plastic deformation rate directly after the elastic limit is attained. Measurements of compression velocity in the plastic shock wave provide data on the material behavior at the follow-on stages and usually at higher deformation rates [17,18].…”