Anomalous acoustic reflection on a sliding interface or a shear band

Area of Science:

• Physics
• Geophysics
• Materials Science

Background:

• Acoustic wave reflection from static interfaces is well-understood.
• Sliding interfaces introduce complex phenomena like energy dissipation and gain.
• Understanding these phenomena is crucial for geophysical and material science applications.

Purpose of the Study:

• To investigate acoustic plane wave reflection from steadily sliding interfaces with velocity-strengthening friction or shear bands.
• To analyze the acoustic impedance and energy conservation of such systems.
• To explore the potential for detecting shear localization using acoustic reflection.

Main Methods:

• Theoretical analysis of acoustic plane wave reflection.
• Modeling of interfaces with velocity-dependent friction and elastic contrast.
• Examination of energy partitioning between frictional dissipation and acoustic energy gain/loss.

Main Results:

• The acoustic impedance of a sliding interface differs significantly from a static one.
• Energy conservation is violated in open systems, with work partitioned between dissipation and coherent acoustic energy.
• Large friction coefficients favor energy gain, while velocity strengthening suppresses it.
• Infinite elastic contrast with Coulomb friction leads to spontaneous acoustic emission, but this is mitigated by velocity strengthening or finite elastic contrast.

Conclusions:

• Positive acoustic energy gain is observable in rough-on-flat multicontact interfaces.
• Sliding shear bands in granular media produce sizable reflections, enabling shear localization detection.
• Acoustic reflection analysis offers a promising method for identifying shear localization phenomena.