Effectiveness of acoustic emission parameters to monitor the crack formation in refractories - Case study on castables of different brittleness

Variability of in-service loads justifies the broad range of microstructures in ceramic refractories used as high temperature industrial insulation. Application of the non-destructive technique of Acoustic Emission (AE) potentially provides an insight into the microstructural response to thermo-mechanical loads and enables rational material development and application. Regarding the multitude of existing AE approaches, effectiveness of a number of AE damage parameters was studied. The AE parameters were obtained in cyclic three-point bending for refractory castables showing different brittleness at failure. No significant damping effects and good correlation with material brittleness was seen for the parameters of event counts, b-value, and AF/RA ratio. The loads introducing critical damage obtained from LOAD and CALM ratios of AE were in agreement with those indicated by AF/RA ratio and event counts during unloading. In the study, the parameter of AF/RA ratio differentiating between shear and tensile failure signals was seen as the most universal criterion.