Periodic Reporting for period 1 - ToughMG (Modeling the fracture toughness of metallic glasses through a multiscale approach)
Reporting period: 2021-10-01 to 2023-09-30
The elasto-plastic deformation of amorphous solids, glasses in particular, and their modes of failure, remain major challenges in mechanics and materials science, with far reaching fundamental and practical implications. At the fundamental level, the irreversible and failure dynamics of glasses pose deep questions about disordered, out-of-equilibrium, driven dissipative systems. Our understanding of failure pathways remains very incomplete and in particular, lags behind our understanding of the corresponding processes in the ordered counterparts of glasses, i.e. in crystalline solids. This research proposal aims to better understand the connection between amorphous microstructures and material resistance to failure. Main research objectives of this action are: (i) building a novel algorithm to detect the field of plastic instabilities in structural glasses, (ii) understanding the nonlinear micromechanics of glassy defects and extracting microscopic flow rules from glassy samples, and (iii) coupling particle based simulations and mesoscopic elasto-plastic models to study strain localization and fracture. Overall, this project has led to the development of new cutting edge microscopic tools that help us to characterize structural and mechanical heterogeneities in structural glasses. We have shown that one can firmly establish a link between microstructures and glassy defects. Furthermore, we have demonstrated that one can extract local flow rules from as-cast glassy samples. The latter opens new avenues including: (i) the systematic and efficient characterization of a large catalog of glasses with different chemical compositions and material preparation histories and (ii) the calibration of mesoscopic models of plasticity to study large scale dissipative collective phenomena, such as the nucleation of shear bands.
In this action, we have developed a new microscopic algorithm to detect plastic defects in structural glasses. For the first time, we have shown that it is possible to extract the complete non-phononic vibrational density of states in structural glasses, such as in Bulk Metallic Glasses. The latter was impossible without the aforementioned detection algorithm. We have also derived a new non-linear formalism based on the strain dynamics of the local stress tensors. This work allows one to measure mechanical heterogeneities in computer glasses. In particular, we have shown that it is possible to use this method to extract local flow rules in bare as-cast configurations. Harvesting the knowledge of the host institutions, in particular in the formulation of mesoscale models of plasticity, we have formulated an elasto-plastic model that takes as input yield stress distributions extracted from atomistic simulations. We have validated our method by predicting the stress-strain response of materials exhibiting a wide range of mechanical stability ranging from ductile to brittle materials. We are currently working on an improvement of our mesoscale model in order to introduce the nucleation and propagation of cracks. In parallel, we have collaborated with an experimental group working on the failure of bulk metallic glasses (BMGs). Combining experimental post-mortem information and particle-based molecular dynamics simulations, we have shed light on the collective competition between shear and dilation plasticity. This work will be valuable in the future to guide us in formulating more refined mesoscopic and macroscopic flow models for amorphous solids. This work has been disseminated across 8 international conferences including both physics and mechanics communities. We have also given a tutorial on microscopic tools at the Lorenz Center in Leiden (NL). This work also features 4 manuscripts with 2 already published in internationally peer reviewed journals. All publications and numerical details are available in open access.
This work has shown that it is possible to measure mechanical disorder in atomistic glasses and parametrize mesoscopic models of plastic to predict the mechanical deformation of materials. This work opens a new avenue to systematically characterize the role of preparation protocol on glass stability and predict the ability of a material to localize plastic flow. This work will also feature an open access library that will help the glass physics and materials science community to comprehend the relation between structure and failure of amorphous solids. Finally, part of this work is currently helping to develop new indicators to measure structural heterogeneities in other classes of disordered solids, namely physical gels and biological networks.