Quantitative description of damage evolution in ductile fracture of tantalum

Abstract

Dynamic ductile fracture has been studied through incipient spallation experiments on two grades of tantalum. A commercially pure Ta material incipiently spalled at 252 m/s, a highly pure Ta material incipiently spalled at 246 m/s, and a highly pure Ta material preshocked at 250 m/s and incipiently spalled at 246 m/s were used. Microstructural parameters of the fracture process such as porosity, void-size distributions, and void aspect ratios have been quantified using image analysis and optical profilometry techniques. The commercially pure Ta, the highly pure Ta preshocked prior to spall, and the annealed high-purity Ta exhibited 27, 16.6, and 5.5 pct porosity, respectively. The void-size distribution observed in all three tests was adequately represented by either a log-normal or a linear combination of a log-normal and a Weibull distribution function. At least 80 pct of the aspect ratios observed in all three tests were adequately represented by a gamma distribution function.

The Morphology of Tensile Failure in Tantalum

“…The metallographic analysis of tantalum spall damage formed at a loading rate of 246 m/s shows very little evidence of microstructural distortion in the vicinity of the voids. [20] With little bulk deformation, void formation occurs at parent grain boundary triple junctions rather than subgrain boundaries. [19] The voids grow spherically to very large sizes, over 100 lm.…”

“…[18][19][20] The current study seeks to evaluate the failure process of tantalum under low rate loading at room temperature both as a means to understand the material's reliability for applications where these environments are relevant, and as a point of departure to later examine highertemperature behavior. Tantalum possesses good ductility at room temperature and maintains modest ductility even down to cryogenic temperatures.…”

“…Under dynamic loading, tantalum fails by a spallation process which progresses by the nucleation of distributed nanoscale voids, followed by void growth and link-up of clusters of voids. [19,20] To further motivate the current study, a preliminary observation of the fracture surface of tantalum was compared with classic ductile, dimpled rupture morphology (Figures 1(b) and 2). This examination of the fracture surface of pure tantalum loaded in quasistatic tension calls into question the validity of traditional void coalescence models for ductile fracture for this material.…”

A multiscale strength model for tantalum over an extended range of strain rates

“…These simulations are conducted assuming adiabatic conditions-energy generated by mechanical work remains in the samples and contributes to temperature rise. For simplicity, these simulations are conducted at constant strain rate corresponding to [19][20][21] Data are plotted as grey  symbols. the nominal experimental condition.…”

Characterization of recompressed spall in copper gas gun targets

“…If the tensile stress is sufficiently high, voids can nucleate around particles or defects in the material and grow. Spall and the resulting damage have been studied extensively for shock loading created by gas guns [1][2][3][4] , explosives [5][6][7][8] and laser ablation [9][10][11] .…”