In a prior work, it was found that grain boundary structure strongly influences damage evolution at grain boundaries in copper samples subjected to either shock compression or incipient spall. Here, several grain boundaries with different grain boundary structures, including a {Sigma}3 (10-1) boundary, are interrogated via conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) to investigate the effects of atomic-scale structural differences on grain boundary strength and mobility. Boundaries are studied both before and after shock compression at a peak shock stress of 10 GPa. Results of the TEM and HRTEM work are used in conjunction with MD modeling to propose a model for shock-induced damage evolution at grain boundary interfaces that is dependent upon coincidence.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Microstructural Evolution during Dynamic Deformation

No abstract prepared.

36 MATERIALS SCIENCE↗

DOE OSTI2012

EFFECT OF TEMPERATURE ON TEXTURE EVOLUTION IN TANTALUM DURING DYNAMIC-EXTRUSION

Motivation of this project is: (1) Build a furnace as a cross section of a gun barrel capable of temperatures up to 600 Celsius; (2) To examine the influence of temperature, texture, and extrusion velocity in Tantalum; (3) Constrain parameters to improve and assist in constitutive model development using high speed imaging & PDV (in-situ); (4) Understanding microstructural development in materials using the dynamic extrusion technique; and (5) Use as a validation test for developing fracture models important to industry, the DoD, and the DOE.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Pressure and Temperature effects on the High Pressure Phase Transformation in Zirconium

At high pressure zirconium is known to undergo a phase transformation from the hexagonal close packed (HCP) alpha phase ({alpha}) to the simple hexagonal omega phase ({omega}). Under conditions of shock loading, the high-pressure omega phase is retained upon release. However, the hysteresis in this transformation is not well represented by equilibrium phase diagrams. For this reason, the influence of peak shock pressure and temperature on the retention of omega phase in Zr is explored in this study. In situ VISAR measurements along with post-mortem metallographic and neutron diffraction characterization of soft recovered specimens have been utilized to quantify the volume fraction of retained omega phase, morphology of the shocked alpha and omega phases, and qualitatively understand the kinetics of this transformation. This understanding of the role of peak shock stress will be utilized to address physics to be encoded in our present macro-scale models.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Effects of Loading Kinetics on the Shock Response of Polycrystalline Copper

The effects of loading kinetics on the damage evolution in high purity copper samples are summarized as follows: The combination of the energy supplied by the shock impulse (peak stress) and the time spent in it dissipation seem to be responsible for the characteristics of the damage fields. For an increasing coupled parameter of energy*time, more damage was predicted, as well as experimentally observed; As more energy (higher peak stress) was dissipated for longer periods of time (lower decompression rate), the damage fields evolved from early stages of damage, in the form of void nucleation and initial void growth, to the later stages of void coalescence.

36 MATERIALS SCIENCE↗