Research Group Peter Schall

Institute of Physics, University of Amsterdam

Fracture of amorphous solids

We encounter amorphous materials everywhere as plastics, window glass, and concrete. Their mechanical properties are central in many of their applications. Fracture presents a serious limit to their applications, demarcating failure of the material. In amorphous materials, slow fracture is of particular interest: in this fracture process, the material can develop cracks over long times, assisted by slow, plastic processes. This slow fracture process in is not well understood, and challenging to study with computer simulations due to the long time scales involved.

We achieve direct particle-scale images of the  slow fracture process using a cohesive colloidal model system. In this system, the particles interact via attractive critical Casimir forces, producing a cohesive amorphous solid that exhibits fracture in very close analogy to atomic amorphous solids. The figures below show a microscope movie of the slow fracture experiment (Fig. 1), and the strain distribution, calculated from the displacements of the individual particles between subsequent frames (Figs. 2 and 3). These direct observations allow us to elucidate the origin of the highly intermittent dynamics of the fracture process due to the interplay of strain-induced weakening and crack propagation.


Figure 1 Direct particle-scale observation of slow fracture in a cohesive colloidal glass.
Figure 2 Strain distribution during slow fracture of the amorphous colloidal solid. Shown is the opening strain component. The flickering reveals the highly intermittent dynamics of the slow fracture process.
Figure 3 Snapshot of the strain distribution. Left: Reconstructed image showing the strain component normal to the crack propagation direction. Right: Strain field magnitude as a function of distance from the crack tip. Good agreement with continuum theory predictions is observed down to a distance of ~50 micrometer from the tip.

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