Compressive creep and indentation behavior of plasticine between 103 and 353 K

We show in this work that the mechanical behaviour of plasticine – a synthetic clay – has much in common with the one of glass. The mechanical behavior of plasticine has been first characterized in compression for temperatures between 103 and 353 K. The yield stress (sy), the stress exponent (n) and the shear viscosity coefficient (ν) were measured as a function of temperature. The indentation behavior is investigated using a 8 cm large Vickers-type indenter and then discussed in the light of the constitutive law. Plasticine exhibits a softening temperature (Ts) at ∼200 K which corresponds to a change in the behaviour from brittle to ductile similar to the one observed in glasses in the glass transition range (Tg). Both typical deformation contributions, namely shear flow and densification, associated with the indentation process in glass were observed in plasticine. The deformation pattern beneath the indenter was observed in some specimens obtained by stacking plasticine layers with different colors and a photomechanics method was developed to investigate the indentation zone geometry. Densification is found to predominate over viscous flow below Ts, and a strongly shear-thinning indentation-creep flow shows up above Ts.