Berlin 2018 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 25: Topical Session (Symposium MM): Fundamentals of Fracture

MM 25.3: Talk

Tuesday, March 13, 2018, 12:15–12:30, TC 006

Fracture properties of silica nanoparticle and clay gels — •Gustavo Gimenes and Elisabeth Bouchaud — PSL Research University, ESPCI Paris, UMR Gulliver, MMN, 6 rue Jean Calvin, 75005 Paris Cedex 05, France

Colloids at low volume fractions can gelate into amorphous solids by their aggregation into a space-filling network. Rheological and mechanical tests over those colloidal gels have shown interesting results such as yield localization and delayed yielding. However, direct observation of their fracture behavior at mesoscopic and microscopic scales is hindered by difficulties in imposing a controlled load on a soft material and by the combination of large deformations and viscoelastic processes.

We use two new experimental setups fabricated with microfluidic technology to study the fracture of aqueous colloidal systems made with silica nanoparticles and synthetic hectorite clay Laponite RD (with diameters around 25 nm). A wide range of behaviors was observed as a function of the ionic strength, particle volume fraction and gel times for both materials, from a linear elastic solid which breaks to a viscoelastic liquid flowing under load. During fracture, the measurement of the displacement fields in the vicinity of the crack tip by Digital Image Correlation and of the crack opening displacement enable the determination of the stress intensity factors and the energy release rates. The comparison of both methods allows us to estimate the size of the non-linear zone, which tends to increase for decreasing ionic strengths. We also evaluate the characteristic time by considering the influence of the crack speed.