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Jonathan T. Uhl

Publications and source records attributed to Jonathan T. Uhl.

3 recordsLinked to original sources

Crystal plasticity as a mean field depinning transition: results from a phase field crystal model

Until now, most of our knowledge about the universality class of crystal plasticity has come from simulations using discrete dislocation dynamics. These are force-controlled, typically at zero temperature, and deal with the creation and annihilation of dislocations phenomenologically. In this work, we go beyond these limitations by using phase field crystal simulations in two dimensions at finite temperature to extract the avalanche statistics of a simulated crystal under constant shear velocity. In addition to the avalanche size and energy distributions we extract the avalanche duration distributions and power spectra. All exponents and scaling functions extracted here for the statics and dynamics of crystal plasticity, belong to the mean field elastic depinning universality class, confirming earlier findings based on discrete dislocation dynamics.

cond-mat.mtrl-sci

Bulk Metallic Glasses Deform via Slip Avalanches

Inelastic deformation of metallic glasses occurs via slip events with avalanche dynamics similar to those of earthquakes. For the first time in these materials, measurements have been obtained with sufficiently high temporal resolution to extract both the exponents and the scaling functions that describe the nature, statistics and dynamics of the slips according to a simple mean-field model. These slips originate from localized deformation in shear bands. The mean-field model describes the slip process as an avalanche of rearrangements of atoms in shear transformation zones (STZs). Small slips show the predicted power-law scaling and correspond to limited propagation of a shear front, while large slips are associated with uniform shear on unconstrained shear bands. The agreement between the model and data across multiple independent measures of slip statistics and dynamics provides compelling evidence for slip avalanches of STZs as the elementary mechanism of inhomogeneous deformation in metallic glasses.

cond-mat.soft

Determination of the universality class of crystal plasticity

Although scaling phenomena have long been documented in crystalline plasticity, the universality class has been difficult to identify due to the rarity of avalanche events, which require large system sizes and long times in order to accurately measure scaling exponents and functions. Here we present comprehensive simulations of two-dimensional dislocation dynamics under shear, using finite-size scaling to extract scaling exponents and the avalanche profile scaling function from time-resolved measurements of slip-avalanches. Our results provide compelling evidence that both the static and dynamic universality classes are consistent with the mean-field interface depinning model.

cond-mat.mtrl-sci