FAilure PREcursors in Soft matter – FAPRES

Material failure is ubiquitous on length scales ranging from a few nanometers, as in fracture of atomic or molecular systems, up to geological scales, as in earthquakes. The detection of any precursors that may point to incipient failure is the Holy Grail in many disciplines, from material science to engineering and geology. Material failure is particularly relevant to soft matter systems (colloids, emulsions, polymers etc.), which are an ideal benchmark to investigate how mechanical stress impacts condensed matter. Indeed, soft matter is very susceptible to even modest mechanical loads and most soft materials can be conveniently investigated by powerful optical methods such as microscopy or light scattering. We propose to use an unprecedented set of original soft model materials and novel experimental and numerical techniques to elucidate at the microscopic level the mechanisms leading to catastrophic events, thereby addressing the following key question: when and why soft materials fail under stress? By answering this question, we aim at establishing robust and quantitative links with other fields where catastrophic events occur, as in geological processes and material science.

We will study the sudden, catastrophic failure observed in a variety of soft solids when an external load is imposed to the material. Very often, material failure is preceded by an induction time, lasting from seconds to several hours or more, during which the material retains its macroscopic integrity and its deformation varies only weakly with time. The main questions we want to answer concern the nature of the microscopic rearrangements during this induction time, and whether the temporal evolution of these microscopic precursors could provide a mean to detect an incipient failure. A key and original feature of our proposal is to focus on dynamical (as opposed to structural) precursors of failure, which we will investigate both experimentally (Partners 1 and 2, Université Montpellier 2) and numerically and analytically (Partner 3, Université Joseph Fourier, Grenoble).

To reach these goals, we will combine an unprecedented set of original soft model materials and novel experimental and numerical techniques.

(i) Thanks to the large panel of experimental systems that we plan to investigate, which are representative of a broad class of materials (dense amorphous systems, dilute network formers, polymer gels, polycrystals), we will acquire a general physical understanding and possibly draw universal features.

(ii) The experimental methods that we will implement combine temporal and spatial resolution typical of imaging techniques with the sensitivity to very small displacements and the possibility to probe in 3D a macroscopic portion of a sample afforded by scattering methods. A novel combination of rheometry and space- and time-resolved light scattering will be implemented and will allow unprecedented sets of data to be collected.

(iii) Finally, our numerical and analytical multiscale approach will cover a wide range of length scales, from the particle level of microscopic simulations to mesoscopic, coarse-grained methods, up to mean field models. State-of-the-art techniques and new parallelization methods will be implemented to circumvent the difficulty in simulating the long range interactions between rare events.

In short, we propose to use an unprecedented set of original soft model materials as well as experimental and numerical techniques to address the following key question: when and why soft materials fail under stress?