Abstract

The criteria of elastic instabilities of solids are understood for 50 years, the physical nature of the elastic collapse for 20 years. We just start to understand the dynamics of such instabilities, in particular in first order transitions. I will show that continuous front propagation (solitons) is virtually always superimposed by jerks and avalanches which give rise to ‘crackling noise’. Continuous measurements in DSC and RUS ignore this contribution while acoustic emission measurements are blind towards the continuous front propagation. I will show that even defect free ferroelastic crystals show crackling noise because jamming by twin boundaries leads to avalanche type progression of transformation fronts. Elastic softening is also observed in metamict minerals such as titanite where dynamic softening overcompensates static hardening.