A new paper entitled "Acoustic Emission-Based Identification of Discontinuous Plastic Flow in Austenitic Stainless Steels" has been published in Metallurgical and Materials Transactions A. The first authors are young researchers from IPPT PAN, Hubert Nejman and Adam Szyszko. The co-authors also include Zbigniew Ranachowski, Jerzy Tabin, and Jan Kawałko from the Academic Centre for Materials and Nanotechnology at AGH University of Krakow. The research was further supported by Adam Brodecki and Mirosław Wyszkowski from the Laboratory of Materials and Structures Testing at IPPT PAN.
The study investigates the phenomenon of discontinuous plastic flow (DPF) in austenitic stainless steels deformed at the temperature of liquid helium (4 K, −269°C). The authors demonstrated that acoustic emission (AE) can detect local deformation events that precede the macroscopic stress drops observed during tensile testing. These findings show that the development of plastic instability is not an instantaneous process but is preceded by a sequence of discrete microstructural events.
Fig. 1 Analysis of spectrograms from uniaxial tensile tests of 316L and 304 austenitic steels at 4 K (-269°C) enabled the identification of precursors of plastic instability associated with discontinuous plastic flow (DPF). The observed acoustic emission signals appeared before abrupt stress drops, indicating the development of local microstructural events preceding macroscopic instability (Fig. 3) [1].
The results demonstrate that acoustic emission is a highly sensitive technique for identifying the early stages of strain localization in austenitic steels. This work provides valuable insight into the mechanisms governing plastic instability in materials at temperatures close to absolute zero.
ESSA Project and Research at Cryogenic Temperatures
A key contribution to the publication was made by young researchers Hubert Nejman and Adam Szyszko, who are involved in the ESSA project (Experimental Identification of Strain Field Evolution in the Cryogenic Temperature Range (4 K, 77 K) in Advanced Materials for Hydrogen and Superconducting Applications), funded by the Polish National Science Centre (NCN) under the SONATA programme.
The ESSA project aims to develop an advanced experimental platform for testing materials at cryogenic temperatures, including 4 K and 77 K. The platform combines conventional mechanical testing with modern measurement techniques such as full-field strain analysis, acoustic emission monitoring, and simultaneous temperature and force measurements. This integrated approach enables researchers to observe the mechanical response of materials, strain localization, and the processes accompanying the development of plastic instability in real time.
The research contributes to a better understanding of the behaviour of materials operating under extreme conditions, particularly those intended for hydrogen technologies and superconducting systems used in large-scale scientific and energy infrastructures.
Young Researchers Advancing Acoustic Emission Methods
Hubert Nejman (Fig. 2), who graduated with a Bachelor's degree in Materials Engineering from the Military University of Technology, works as a welded structures designer at Kurspaw and is currently pursuing a Master's degree in Materials Engineering at Warsaw University of Technology. As part of the project, he developed the so-called AE "carpets"—acoustic emission spectrograms that visualize the acoustic activity associated with the evolution of discontinuous plastic flow. These analyses enabled the identification of characteristic acoustic signals appearing before the onset of macroscopic plastic instability. The detection of these precursors was made possible by the advanced AE system developed by Zbigniew Ranachowski from the Non-Destructive Testing Laboratory at IPPT PAN.
Adam Szyszko (Fig. 3), a graduate in Materials Engineering from Warsaw University of Technology and currently a PhD student at the IPPT PAN Doctoral School, specializes in microstructural characterization and the kinetics of deformation-induced martensitic transformation. His research establishes a direct link between the mechanical and acoustic response of austenitic steels and the local microstructural changes occurring during deformation.
Publication:
Tabin, J., Nejman, H., Szyszko, A., Ranachowski, Z., & Kawałko, J. (2026). Acoustic Emission-Based Identification of Discontinuous Plastic Flow in Austenitic Stainless Steels. Metallurgical and Materials Transactions A. https://doi.org/10.1007/s11661-026-08252-6
Fig. 2 Work at the experimental platform for tensile test at cryogenic temperatures in the Laboratory of Materials and Structures Testing at IPPT PAN. In the photo: Hubert Nejman and Mirosław Wyszkowski.
Figj. 3 (a) Installation of the specimen in a cryostat. In the photo: Adam Szyszko; (b) Experimental platform for tensile test at cryogenic temperatures, enabling simultaneous measurement of the strain field using DIC, acoustic emission (AE), temperature, force, and specimen elongation. Evolution of the strain field during a uniaxial tensile test at 77 K.
