High-rate strength response of tantalum from dynamic hole closure experiments

The science and engineering communities have significant interest in experimental platforms to evaluate and improve models for dynamic material deformation. While well-developed platforms exist, there are still gaps to fill for strain and strain rate conditions accessed during impact and other high-rate loading scenarios. To fill one such gap for strength measurements, a platform was recently developed that accesses high strain rate (>= 10(5)/s) and large strain (>= 50%) conditions by measuring the transient closure of a cylindrical hole using in situ x-ray imaging. In the work reported here, further refinement of the platform is performed to reduce the potential effects of porosity and anelasticity on the measurement. This helps us to isolate the strength effects that are the focus of the experiment. The updated experimental configuration employs a two-layer flyer design and elongated target to reduce the magnitude of the tensile excursions associated with rarefaction wave interactions. This allows for a more direct assessment of strength models commonly used for dynamic simulations of metals. We apply the new technique to well-characterized tantalum material, allowing for a robust connection to other experimental techniques. Deformation localization can be a concern in large strain experiments, and to help inform future use of the experimental platform, we use simulations with a sub-zone treatment of shear banding to explore potential localization behavior. Overall, we develop and utilize an experimental configuration with improved isolation of strength effects that can be applied to an expanded range of materials.

Automated summary

The science and engineering communities have a strong interest in experimental platforms to assess and enhance dynamic material deformation models. Although well-developed platforms already exist, there are still gaps to fill for strain and strain rate conditions encountered during impact and other high-rate loading scenarios. A recently developed platform addresses one such gap by utilizing in situ x-ray imaging to measure the transient closure of a cylindrical hole, allowing access to high strain rate and large strain conditions. In this study, further refinements were made to minimize the potential effects of porosity and anelasticity on the measurements, thereby isolating the strength effects for experimentation. The updated experimental setup employs a two-layer flyer design and elongated target to reduce tensile excursions associated with rarefaction wave interactions and enables direct assessment of commonly used strength models for dynamic metal simulations. The technique was applied to well-characterized tantalum material, establishing a robust connection to other experimental techniques. Additionally, simulations were conducted to explore potential deformation localization behavior using a sub-zone treatment of shear banding. Overall, an improved experimental configuration was developed and utilized to isolate strength effects in a wider range of materials.