Use of extension testing to investigate the influence of finite strain on the rheological behaviour of marble

Most mechanical testing of rocks at high temperatures is carried out under axisymmetric triaxial shortening to small ( 1000%) axisymmetric extension tests on Carrara marble at 700°C and 800°C, in the form of strain-time plots for the evolution of material sections through the sample at different distances from the neck. At 800°C, it is clear that total dynamic recrystallization by grain boundary migration is accompanied by substantial mechanical weakening, but sufficient strain could not be applied to reach the steady-state condition for the recrystallized material. The recrystallization is interpreted to produce weakening because the migration of grain boundaries sweeps grains clear of accumulating dislocation density faster than recovery by dislocation climb. In nature, such mechanical weakening would be expected to favour the stable development of a localized zone of deformation. © 1998 Elsevier Science Ltd.