Multiple Avalanche Processes in Acoustic Emission Spectroscopy: Multibranching of the Energy-Amplitude Scaling

Several physical processes can conspire to generate avalanches in materials. Such processes include avalanche mechanisms like dislocation movements, friction processes by pinning magnetic domain walls, moving dislocation tangles, hole collapse in porous materials, collisions of ferroelectric and ferroelastic domain boundaries, kinks in interfaces, and many more. Known methods to distinguish between these species which allow the physical identification of multiavalanche processes are reviewed. A new approach where the scaling relationship between the avalanche energies E and amplitudes A is considered is then described. Avalanches with single mechanisms scale experimentally as E = S(i)A(i)(2). The energy E reflects the duration D of the avalanche and A(t), the temporal amplitude. The scaling prefactor S depends explicitly on the duration of the avalanche and on details of the avalanche profiles. It is reported that S is not a universal constant but assumes different values depending on the avalanche mechanism. If avalanches coincide, they can still show multivalued scaling between E and A with different S-values for each branch. Examples for this multibranching effect in low-Ni 316L stainless steel, 316L stainless steel, polycrystalline Ni, TC21 titanium alloy, and a Fe40Mn40Co10Cr10 high-entropy alloy are shown.

Automated summary

This article introduces various physical processes that can cause avalanches in materials, as well as methods to distinguish between these processes and a new approach to measure the relationship between avalanche energy and amplitude. It is noted that the energy and amplitude of avalanches are not universal constants, but depend on the avalanche mechanism, with examples of multi-branching effects shown in different materials.