ACOUSTIC-EMISSION GENERATED BY THERMOMECHANICAL PROCESSES

The acoustic emission activity generated during temperature changes in different materials was investigated. In high-temperature ceramic sup erconductors groups of acoustic emission signals appear slightlY below the temperature of transition of the superconductor to the normal sta te (88 K). The distribution of the signals depend on the intensity of the current passing through the superconductor, however they appear al so in the non-current state. Acoustic emission activity in the tempera ture range 180 divided-by 210 K was observed as well. Concrete samples heated to a temperature of 100-degrees-C showed during heating an app earance of high frequencies (200 - 500 kHz), and low frequencies (50 - 80 kHz), the sum of events depending on the composition of the concre te. Thermal treatment during the production of concrete causes the app earance of micro-cracks, which produce acoustic emission activity, how ever during the thermal treatment of steel high-pressure pipes this ef fect was not noted. During the melting and cooling of sulphur in certa in circumstances a distinct asymmetry of acoustic emission activity wa s observed.