arXiv subjects

Thomas R. Bieler

Publications and source records attributed to Thomas R. Bieler.

4 recordsLinked to original sources

arXiv2024

$β$ orientation reconstruction and shear deformation calculation in hcp-bcc-hcp phase transformation

We introduce a cluster-based technique to automate pixel-wise reconstruction of $β$ orientations from parent $α$ orientations over large, indexed regions. This approach provides a valuable tool for analyzing problems that require historical information about current $α$ microstructures, such as investigating variant selection mechanisms during the $α\to β\to α$ transformation. Additionally, we present a method for calculating deformation gradient variants associated with phase transformations between hcp ($α$) and bcc ($β$) phases based upon a series of frame rotations and shape transformations. This method streamlines the integration of transformation kinematics into continuum-based models by enabling convenient computation of the deformation gradient governing the transformation.

cond-mat.mtrl-sci↗

arXiv2024

A computational study of how surfaces affect slip family activity

Plastic deformation behavior is most conveniently assessed by characterization on a surface, but whether such observations are representative of bulk properties is uncertain. Motivated by reported inconsistencies in slip resistance probed at different depths, we investigated (i) whether the average slip family activity is affected by the presence of a surface and (ii) how the kinematic nature of available slip families influences a potential surface effect. The slip family activity as a function of distance from the surface was extracted from full-field crystal plasticity simulations of random polycrystalline hexagonal close-packed (HCP) and body-centered cubic (BCC) metals as examples of mixed in contrast to universally-high numbers of slip systems per family. Under certain conditions, a deviation from bulk slip activity is observed up to about two grains from the surface. For the easiest (least slip-resistant) family, a surface effect of decreasing activity with depth emerges if the number of slip systems falls below about six. For harder families, slip activity always increases with depth. These phenomena are explained on the basis of varying constraints with depth in connection with the kinematic properties of slip families in the material.

cond-mat.mtrl-sci↗

arXiv2020

Grain boundary slip transfer classification and metric selection with artificial neural networks

An artificial neural network is used to evaluate the effectiveness of six metrics and their combinations to assess whether slip transfers across grain boundaries in coarse-grained oligocrystalline Al foils \citep{Bieler_etal2019_2,Alizadeh_etal2020}. This approach extends the one- or two-dimensional projections formerly applied to analyze slip transfer. The accuracy of this binary classification reaches around \pcnt{87} for the best single metric and around \pcnt{90} when considering two or more metrics simultaneously. The results suggest slip transfer mostly depends on the geometric relationship between grains. Training a double-layer network having \num{10} nodes per hidden layer with \num{40} measurements is sufficient to render the maximum accuracy.

cond-mat.mtrl-sci↗

arXiv2013

Near-Field Microwave Magnetic Nanoscopy of Superconducting Radio Frequency Cavity Materials

A localized measurement of the RF critical field on superconducting radio frequency (SRF) cavity materials is a key step to identify specific defects that produce quenches of SRF cavities. Two new measurements are performed to demonstrate these capabilities with a novel near-field scanning probe microwave microscope. The first is a third harmonic nonlinear measurement on a high Residual- Resistance-Ratio bulk Nb sample showing strong localized nonlinear response for the first time, with surface RF magnetic field $B_{surface} \sim 10^{2}$ $mT$. The second is a raster scanned harmonic response image on a high quality $MgB_{2}$ thin film demonstrating a quench defect-free surface over large areas.

cond-mat.supr-con↗