Determination and interpretation of statistics of spatially resolved waveforms in spalled tantalum from 7 to 13 GPa

• Published in: International journal of plasticity Vol. 25; no. 4; pp. 587 - 602
• Main Authors: Furnish, Michael D., Chhabildas, Lalit C., Reinhart, William D., Trott, Wayne M., Vogler, Tracy J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2009; Elsevier
• Subjects: Dynamic fracture; Exact sciences and technology; Fracture mechanics (crack, fatigue, damage...); Fundamental areas of phenomenology (including applications); Inelasticity (thermoplasticity, viscoplasticity...); Metallic material; Microstructures; Physics; Plate impact; Probability and statistics; Samples; Solid mechanics; Spalling; Statistical analysis; Statistical methods; Statistics; Strength; Structural and continuum mechanics; Tantalum; Texture; Dynamic fracture; Probability and statistics; Microstructures; Plate impact; Metallic material; Optical interferometry; Hugoniot curve; Variability; Speed measurement; Texture; Mictostructures; Inelasticity; Cavity; Defect structure; Weibull distribution; Rupture strength; Grain size; Statistical analysis; Probabilistic approach; Experimental study; Real time; Cavitation; Axial symmetry; Plate; Tantalum; Lidar; Scaling; Yield strength; Microstructure
• ISSN: 0749-6419; 1879-2154
• DOI: 10.1016/j.ijplas.2008.12.007

A suite of impact experiments was conducted to assess spatial variability in the dynamic properties of tantalum, on length scales of tens of microns to a few millimeters. Two different sample types were used: tantalum processed to yield a uniform refined grain structure (grain size ∼20 μm) with a strong axisymmetric {1 1 1} crystallographic texture, and tantalum processed to yield an equiaxial structure with grain size ∼42 μm. Impact experiments were conducted loading the samples to stress levels from 6 to 12 GPa, which are well above the Hugoniot Elastic Limit (HEL), then pulling the sample into sufficient tension to produce spall. These stress levels were specifically chosen to investigate the spall behavior of tantalum at levels ranging from the incipient spall stage to significantly above the spall strength, focusing on microstructural phenomena. A recently developed spatially resolved velocity interferometer known as the line-imaging VISAR allowed the point-to-point variability of the spall strength to be determined. Specifically, we have been able to determine in real time the nucleation and growth of void defect structures that lead to the eventual spallation or delaminating of the plate. Experiments indicate that the nucleation and growth process is time-dependent and heterogeneous since a time-dependent distribution of defects is measured. This strongly suggests that the spall strength of the material is not a single-valued function. When fitted to Weibull failure statistics, the results indicate a similar mean value and variability for the spall strength of both types of tantalum. The spatial dependence of the material distension of the spalled tantalum is also deduced, in the approximation of uniaxial strain.