Strain intermittency due to avalanches in ferroelastic and porous materials

The avalanche statistics in porous materials and ferroelastic domain wall systems has been studied for slowly increasing compressive uniaxial stress with stress rates between 0.2 and 17 kPa s(-1). Velocity peaks v(m) = dh/dt are calculated from the measured strain drops and used to determine the corresponding Energy distributions N(E v(m)(2)). Power law distributions N(v(m)(2)) proportional to (v(m)(2))(-epsilon) have been obtained over 4-6 decades. For most of the porous materials and domain wall systems an exponent epsilon = 1.5 +/- 0.1 was obtained in good agreement with mean-field theory of the interface pinning transition. For charcoal, shale and calcareous schist we found significant deviations of the exponents from mean-field values in agreement with recent acoustic emission experiments.