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, managed by Dr. D. Farkas), and we are very grateful for the financial support we receive.

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

Here we directly measure the spatiotemVelocityDistributionporal 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 between fcc and bcc in the velocity relaxation of time-resolved avalanche shapes. 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. Stay tuned, and follow our next research activities that examine collective dislocation dynamics.

Selected publications:
Small-scale plasticity – Insights into dislocation avalanche velocities
Independence of Slip Velocities on Applied Stress in Small Crystals
Spatiotemporal slip dynamics during deformation of gold micro-crystals

Avalanche statistics in micro-crystals

Single crystalline micro-scale pillars deform in discrete bursts in analogy to plate tectonics. Their probability distribution follows a power-law with a stress-dependent cutoff. Properties of the Scaling Collapse Paper Mattsystem, 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 if experimental boundary conditions affect the universality of the probability distributions. The boundary conditions considered are force-controlled mode and displacement-controlled mode and our study of 1, 3, and 5 µm diameter single-crystalline Au pillars shows that boundary conditions do not affect the distribution of slip sizes via a predicted scaling collapse. The critical exponents and scaling functions are thus the same regardless of boundary condition, which has implications for other systems, such as, ferromagnets, earthquakes, and the stock market.

Selected publications:
Slip statistics of dislocation avalanches under different loading modes