ELFT HÍRADÓ

[Janos Asboth <asboth.janos AT ttk.bme.hu>]

Meghívó

BME Elméleti Fizika Szeminárium,

okt. 21. péntek 10h15,

1111 Budapest, Budafoki út 8., BME F III. magasföldszint 01.,
Elméleti Fizika Tanszék szemináriumi szoba

Ispánovity Péter (ELTE Anyagfizika Tanszék):
Experimental and numerical investigation of dislocation avalanches

Plastic deformation of metals usually occurs as a series of rapid and
localized deformation events of various sizes. During these events, the
line-like defects of the crystal lattice, called dislocations, move
collectively in a local part of the crystal. The experimental investigation
of this avalanche-like phenomenon was initially carried out on bulk samples
using acoustic emission (AE) measurements. It was found that the
distribution of both the energy and amplitude of individual events are
scale-free, which indicates the critical nature of plastic deformation.
This phenomenon was later also observed during the compression of
micropillars, typically a few um in size, where it manifests in random
jumps in the stress-strain curve.

In the first half of the lecture, the outcome of the combination of these
two experimental techniques will be presented, the aim of which was to
obtain a more detailed picture of the dynamics of dislocation avalanches.
To this end, micropillars were milled from Zn single crystals using the
focused ion beam technique. The samples were attached to an AE sensor and
compressed in situ in a scanning electron microscope using a special device
designed for this purpose. We found that the acoustic events measured
during compression are perfectly correlated with the stress drops
experienced during compression. The statistical analysis of the data
obtained by the two methods revealed the complex spatio-temporal dynamics
of a single stress drop: a dislocation avalanche consists of many smaller
events that show similarities to earthquakes through different
phenomenological laws. These results, which are also confirmed by discrete
dislocation dynamics simulations, provide the missing link between the
quantities measured by AE and the mechanical characteristics of individual
events [1]. As a continuation of the research, we present the stability
analysis of the discrete dislocation systems, which reveals the development
of dynamic modes that can span the entire volume. The emergence of these
modes provides an explanation for the previously experienced anomalous
system size dependence of avalanche sizes and the unusual behavior of local
flow stresses [2].

[1] PD Ispánovity, D Ugi, G Péterffy, M Knapek, Sz Kalácska, D Tüzes, Z
Dankházi, K Máthis, F Chmelík, I Groma, Nature Communications 13, 10 (2022).
[2] D Berta, G Péterffy, PD Ispánovity, arXiv:2202.08224 (2022).

Minden érdeklődőt szeretettel várunk.
Asbóth János,
 szemináriumi koordinátor