Crackling noise in disordered materials

Recent experimental and theoretical progress on the study of crackling noise in the plastic deformation of crystals, ferroelastics, and porous materials is reviewed. We specifically point out opportunities and potential pitfalls in this approach to the study of the nonequilibrium dynamics of disordered materials. Direct optical observation of domain boundary movement under stress and experimental results from acoustic emission and heat-flux measurements lead to power-law scaling of the jerk distribution with energy exponents between 1.3 and 2.3. The collapse of porous materials under stress leads to exceptionally large intervals of power-law scaling (seven decades). Applications in geology and materials sciences are discussed.