Intermittent Plastic Flow

Small crystals offer unseen possibilities to study some fundamental aspects of plastic deformation. One of them is that plastic flow is intermittent and to some degree scale-free. We use advanced small-scale mechanical testing methods to unravel time-resolved and statistical properties of intermittent flow. Our current efforts in this research area are supported by the NSF CAREER program (DMR-MMN), and we are very grateful for the financial support we receive.

Nontrivial scaling exponents of avalanche statistics in microplasticity

Single crystalline micro-scale crystals deform in discrete bursts in analogy to plate tectonics. Their probability distribution follows a power-law with an exponential cutoff. Properties of the system, such as, symmetry, dimension, and interaction range, dictate the universality class, and thus the statistical properties, of the system. In collaboration with the group of Prof. Karin Dahmen, we here investigate the parameters that affect the scaling behavior of the probability distributions. Whilst many reports argue for universal scaling exponents in microplasticity, we find clear experimental evidence that this is not the case. Indeed, many material specific properties are sensitively affecting the statistical signature of intermittent plastic flow. The novel developments open up avenues to incorporate material-specific details into statistical deformation models.

Slip kinetics during intermittent flow of nano- and micro-crystals

Here we directly measure the spatiotemporal characteristics of dislocation avalanches during plastic flow of nano- and micro-crystals. This ongoing project reveals intriguing findings, such as an insensitivity of the dislocation avalanche to applied stress. We also find remarkable differences in the velocity relaxation of time-resolved avalanche shapes in fcc and bcc crystals that both depend on crystal orientation and initial dislocation density. Our experimental results are used to test emerging models for general avalanches dynamics. Even though theory predicts a universal behavior in avalanche dynamics across all metals, we find deviations from such behavior and non-trivial exponents. Stay tuned, and follow our next research activities that examine collective dislocation dynamics.

Selected publications:

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.