Bleyer, JeremyMolinari, Jean-François2018-03-142018-03-142018-03-14201710.1063/1.4980064https://infoscience.epfl.ch/handle/20.500.14299/145557The microbranching instability occurring for rapidly propagating cracks in brittle materials has been described in various experiments as an intrinsically three-dimensional phenomenon. Using a variational phase-field model, we show that the microbranching process is, indeed, a three-dimensional instability which exhibits a strong dependence on the sample width and can be suppressed for very thin samples. We show that the phase-field internal length scale is the decisive variable governing the branching pattern, which can be either localized in the transverse direction as observed in a glass, for example, or, on the contrary, almost translational invariant with quasi-periodic structures, as observed in PMMA. © 2017 Author(s).Phase interfaces, Wakestext::journal::journal article::research article