Résumé:

Crack initiation and propagation have been previously studied in our group for model complex fluids using pendant drop experiments [1].We will present here experimental results obtained in a radial Hele Shaw cell, where crack propagation can be better controlled and followed over longer time, once initiated by pushing the complex fluids with a low viscous oil. We use self-assembled transient networks with tunable morphology for which rheology data suggest a brittle to ductile transition [2]. We characterize the crack morphology and speed thanks to imaging with a high speed camera and couple these data to the complex fluids displacement fields around the crack as obtained by particle image velocimetry (fig. 1). Using crossed polarizers, we moreover measure the birefringence of the samples under flow (fig. 2) allowing us to relate the crack properties to the structural properties of the complex fluids and to identify the process zone at the vicinity of the crack tip. Thanks to our space and time-resolved measurements, the mechanisms at play in a brittle to ductile transition in complex fluids could be elucidated.