Deciphering Acoustic Emission Sources during Particulate-Continuum Contact Shearing

Abstract

This study explores acoustic emission (AE) generation during shearing at coarse particulate–continuum material contacts using a custom-designed micromechanical direct shear apparatus. Through a detailed quantitative micromechanical investigation, it provides new insights into the relationship between AE activity and particle-level contact mechanisms, offering a foundation for advancing AE-based applications. The influence of particle tip geometry, material hardness, surface roughness, normal load, and kinematic freedom on AE and shear responses was systematically evaluated. The results suggest that, under the measurement configuration used in this study, AE was not detected during pure sliding or plowing unless material degradation occurred. Distinct AE bursts are linked to tip breakage, wear, rearrangement, and microtapping, with softer and rougher materials promoting greater AE due to enhanced asperity engagement and contact degradation. Particles with moderate tip angles and constrained motion formed more effective acoustic contacts, resulting in significant shear force drops and AE activity. Additionally, the axis ratio and freedom of particle movement influenced whether sliding, rotation, or rearrangement dominated, thereby altering AE patterns. Rough surfaces amplified AE response by increasing tip wear and interlocking, while smoother interfaces with blunt particles often resulted in acoustic blindness. These findings provide direct evidence of the micromechanical mechanisms responsible for AE in particulate interfaces and highlight the role of tribological interactions in governing shear and AE responses.