Search NASA⌕ Search

Engineering topics

Vasin, Roman

Publications and source records attributed to Vasin, Roman.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A simple variant selection in stress-driven martensitic transformation

Significance Variant selection plays an important role during martensitic transformations in both metals and oxides. Due to its great effects on the crystallographic texture, it has received a great deal of attention in fields of physics, material science, and even Earth science. Previously, most studies focused on transitions in metals induced by temperature. Here, we investigate more complex oxides structures during the pressure/stress-driven martensitic transformation and find a very simple variant selection in cubic/orthorhombic Mn 2 O 3 . The high-pressure orthorhombic phase inherits texture from the low-pressure cubic phase. Only one of the six cubic {110} planes becomes the orthorhombic (100) plane: the one perpendicular to the compression direction. This will become a reference to demonstrate the variant selection behavior under high pressure.

42 ENGINEERING↗
DOE OSTI2015

Linking preferred orientations to elastic anisotropy in Muderong Shale, Australia

The significance of shales as unconventional hydrocarbon reservoirs, nuclear waste repositories, and geological carbon storage has opened new research frontiers in geophysics. Among many of its unique physical properties, elastic anisotropy has long been investigated by both experimental and computational approaches. Here we calculate elastic properties of Cretaceous Muderong Shale from Australia with a self-consistent averaging method based on microstructural information. The volume fraction and crystallographic preferred orientation distributions of constituent minerals are based on synchrotron X-ray diffraction experiments. Aspect ratios of minerals and pores, determined from scanning electron microscopy (SEM), are introduced in the self-consistent averaging. Our analysis suggests that phyllosilicates (i.e., illite-mica, illite-smectite, kaolinite, and chlorite) are dominant with ~70 vol.%. The shape of clay platelets displays an average aspect ratio of 0.05. These platelets are aligned parallel to the bedding plane with a rather high degree of preferred orientation. The estimated porosity at ambient pressure is ~17 vol.% and is divided into equiaxial pores and flat pores with an average aspect ratio of 0.01. Our model shows results (e.g. at pressure of ~50 MPa with C 11 = 26.3; C 13 =12.5; C 33 = 18.2; C 44 = 2.8; C 66 = 6.8 [GPa]) that compare satisfactorily with values derived from ultrasonic velocity measurements (C 11 = 26.6; C 13 = 16.2; C 33 = 18.3; C 44 = 4.5; C 66 = 8.8 [GPa]), confirming the validity and reliability of our approximations and averaging approach.

58 GEOSCIENCES↗