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J. Scheibert, C. Guerra, F. Célarié, D. Dalmas and D. Bonamy

Depending on their fracture mode, materials are traditionally gathered into three distinct classes:

  • (i) ductile materials that like metals deform plastically before their fracture
  • (ii) quasi-brittle materials such as rock or concrete, where "non-visible" damage starts to accumulate through microcracking, up to coalescence that yields to catastrophic failure.
  • (iii) brittle materials like oxide or polymer glasses... that deform elastically up to their fracture. This occurs through the successive breaking of atomic bonds at the crack tip. 

Experiments performed at IRAMIS-SPCSI show that a given material may, depending on the crack velocity, belong to two of these categories: Plexiglas®, archetype of brittle material, is found to damage through the nucleation of microcracks like quasi-brittle materials, beyond a well defined crack speed.


D. Bonamy and L. Ponson (SPCSI), D. Santucci (Fysik Institutt Oslo)

Fracture is a phenomenon of everyday life: it is observable at all scales of condensed matter, from the atomic scale (in nanostructures) to the scale of our planet marked by fractures in the continental plates. But, can we find a unifying model to describe the phenomenon?

The dynamics of fracture is complex. In an ideal elastic material, perfectly homogenous, the situation remains relatively simple by means of the Elastic Linear Mechanics: the crack front is a smooth line, crossing the material with a predictable trajectory and at a regular speed that is function of the solicitation in tension. Taking into account the inhomogeneities inherent in any material (microstructure heterogeneities, point defects, temperature…) the crack no more propagate continuously but by apparently unpredictable leaps, which imposes a statistical treatment of the problem.

 

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