CECAM - Failure in soft materials: from yielding to fractureFailure in soft materials: from yielding to fracture

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Many amorphous soft systems exhibit spectacular transitions when subjected to external forces and deformations. One of the more captivating examples is the yielding transition, which unites systems as disparate as gels, glasses, foams, and granular materials [1]: while for small external drives these materials behave substantially elastically, when the driving becomes sufficiently large, they undergo microscopic plastic rearrangements and macroscopic flow. Due to the amorphous nature of these materials, immediate use of theoretical descriptions that work successfully for crystalline solids is prevented. Recent theoretical [2,3], numerical [4,5] and experimental [6,7] approaches have been making progresses to link the emerging macroscopic rheological behavior to the underlying microscopic events [8], however outstanding questions remain and our current understanding of the yielding transition remains incomplete [9].

Quite intriguingly, many living tissues are also subjected to mechanical stresses that, in addition to being external, can also arise from internal physiological processes at the cellular level. As a consequence, one can observe tissue fracture [10], as well as jamming [11] and unjamming [12] transitions that resemble those observed in inert systems, while at the same time playing a key role in physiologically relevant processes such as embryogenesis [13] and cancer growth [14].

The analogies between the rheological behavior of inert and living soft materials is becoming so evident and compelling that cell tissues have been considered as active foams [15], or yield-stress materials [16] that exhibit shear-driven solidification [17] or brittle-to-ductile transitions [18], also accompanied by activation of topological defects [19], just like their inert counterparts. The deeper understanding of the yielding transition, and of its emergence from the relevant microscopic processes, in inert soft matter [1,3,20-22], has therefore important potential implications for the fundamental understanding of living soft materials and tissues. Vice versa, mimicking remedial strategies that are known to work for living soft materials can drive the design of improved artificial materials.

With this workshop, our objective is to bring together various communities that heavily rely on universal concepts like mechanical response and failure. We firmly believe that there are numerous unresolved questions and ideas that can encourage a fruitful exchange of knowledge between these communities. Consistent with the CECAM tradition, computer simulations are of utmost importance in these fields, serving as both a guiding tool for experiments and a modeling resource when theoretical approaches fall short. Furthermore, in the forthcoming years, the emerging AI/ML paradigm will significantly influence all fields of physics. By inviting experts in this domain, we aim to facilitate an open and comprehensive discussion regarding the impact of such paradigm on the workshop's research themes.

We thus see two emerging topics that are being developed in parallel by different communities, sometimes with partial overlap.

Topic 1: Inert Soft Materials - Phases, Transitions, and Rheological Properties
Inert soft materials exhibit significant non-linear responses to mechanical solicitations, producing intertwined effects of viscoelasticity, plasticity, and memory [23-25]. Investigating microscopic processes is challenging due to their vast range of time and length scales [21,22,26]. However, advancements in experimental techniques and computer simulations are beginning to offer novel insights [6,9,27-30]. In glass physics, yielding, annealing, avalanches, and memory have been explored [31-35]. Major questions include identifying key microscopic timescales and processes governing yielding, brittleness, ductility, stress relaxation, and overall nonlinear response.

Topic 2: Living Soft Materials - Phases, Transitions, and Rheological Properties
Various biological processes hinge on cell rearrangements in tissues. When parameters such as density, motility, cell-cell adhesion, and cortical tension are altered, tissues may undergo transitions from liquid-like to solid-like states [12,-14,36-40]. These transitions impact the tissue's rheological properties [13,15,17,18], though a systematic study correlating rigidity and microscopic dynamics is still needed. Major questions involve rheological characterization at multiple scales, understanding rheology from a multiscale perspective, the sequence of biophysical steps leading to tissue failure [10,41,42], predicting failure based on microscopic precursors, and the applicability of remedial strategies from living materials to inert soft materials.

Failure in soft materials: from yielding to fracture

Location: Erwin Schrödinger Institut Vienna

Organisers

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