Influence of damage in the acoustic emission parameters

Acoustic emission (AE) is a Non Destructive Inspection Technique, widely used for monitoring of structural condition of different materials like concrete, masonry and rock. It utilizes the transient elastic waves after each fracture occurrence, which are captured by sensors on the surface. Several parameters of the AE behavior enlighten the damage stage within the material. These may be the cumulative AE activity, which is connected to the density of cracks and the emission energy which is connected to the cracks’ intensity. Additionally, AE waveform parameters like duration and frequency content depend on the motion of the crack tip and therefore, carry information about the mode of the crack. Study of the AE indices enlightens the fracture process, enabling predictions on the remaining life. However, the experimental conditions crucially affect the waveforms captured by the sensors. Specimen size, as well as sensor type and sensors separation distance exercise strong influence in the acoustic emission parameters. Since AE features like amplitude and energy are used for characterization purposes in the framework of an energy density approach and frequency is used in cracking mode classification schemes, the influence of the above mentioned experimental parameters should be certainly taken into account in order to lead to more accurate results and increase reliability. This would help to expand the use of AE in situ which so far is hindered by geometric and other technical reasons that allow only a case-specific approach. In the present paper fracture experiments in different specimen sizes of cementitious and rock materials are described while the sensor location relatively to the cracking zone is altered. The aim of this study is to validate the use of cracking characterization in laboratory and check the extension for similar schemes in real size structures with a multiscale methodology.