Fluage en compression d'un smectique B

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We describe two regimes of creep observed under a compression normal to the layers in the B phase of 40.8 (butyloxybenzilidene octylaniline) : both are characterized by a linear dependence of the strain rate versus stress and by the same apparent activation energy. A vacancy mechanism is proposed. For weak stresses, the grain boundaries of the polycrystal act as vacancy sources and sinks; the creep is then governed by the intragranular diffusion of the vacancy (Nabarro-Herring creep). For greater stresses, edge dislocations also act as vacancy sources or sinks and participate in the strain by pure climb (Harper-Dorn type creep). These experiments confirm the crystalline structure of the B phase.