Some Statistical Parameters of Acoustic Emission Signals in Porous Iron under Static Loading

摘要

Acoustic Emission (AE) method is based on detection of ultrasonic signal due to the process of plastic deformation and fracturing of a loaded material. In this paper two characteristics of the AE signal, distributions of time intervals between successive pulses and amplitude distributions of these pulses were obtained. Samples were made of the porous iron with a porosity in the range P=0.05-0.25. This class of materials can be considered as a model to study the influence of geometry of the inhomogeneous medium and percolation effects (due to changing of porosity) on the processes of deformation and fracture, and therefore the behavior of the various parameters of acoustic emission. Registered signals were broadband in a range of frequencies from 100 to 800 kHz. Consideration of amplitude distributions of AE signals showed that it is possible to identify two groups of AE pulses - low-amplitude and high-amplitude in the recorded signals. The first group corresponds to the plastic deformation of the compact sites of the material, and the latter one is usually generated by large plastic shears and crack propagation. It was showed that they have scaling with exponents vary with changes in porosity. Obtained distributions can be perceived as indirect evidence of self-organized processes occurring in porous metallic materials.