Rheology of plasticine used as rock analogue: the impact of temperature, composition and strain

Uniaxial compression tests have been carried out to determine the temperature-dependent rheology of plasticine commonly used for tectonic modelling. The original plasticine types (Kolb brown, Beckʹs orange, Beckʹs green, Weible special soft) are characterized by strain-rate softening with power law exponents (n) and apparent viscosities (η) ranging from 5.8 to 7.3 and 3.4×105 to 2.2×107 Pa s, respectively (if e=10%, Ė=4×10−3 s−1, and T=25 °C). Beckʹs orange shows steady-state creep, whereas the other types show strain hardening. The activation energy, determined for 20 °C≤T≤35 °C, is ranging from 323±34 to 488±22 kJ mol−1. A rise in temperature results in linear decreases of n and η and a reduction in the degree of strain hardening. Steady-state creep and major changes in n and η have further been observed at decreasing filler-matrix ratios, the latter being obtained by adding oil to the original plasticine. The new results suggest that plasticine can be used to model the deformation of natural rocks undergoing dislocation creep. Various rock analogues with strain hardening or steady-state creep, and prescribed stress exponents ranging from 3.4 to 12.3, can be easily produced by changing the temperature and/or the filler-matrix ratio of commercial plasticine types.