Bergner, F.F.BergnerKöhler, B.B.Köhler2022-03-092022-03-091996https://publica.fraunhofer.de/handle/publica/326794A short review on applications of ultrasonic methods including acoustic emission, scanning acoustic microscopy, and surface wave scattering in the field of indentation fracture toughness testing of brittle materials is given. A problem not solved so far is the nondestructive testing of Hertzian cone cracks in opaque materials. The results of three experimental approaches are discussed: Scanning acoustic microscopy is capable of measuring the local cone angle, but there has been no indication of the crack tip. C-mode scanning permits the determination of the cone diameter, but a calibration is necessary. Time-of-flight measurements have the potential to provide both cone diameter and cone depth simultaneously.enacousticacoustic microscopyc-mode imagingcone crackemissionfracture toughnessHertzian indentationsoda-lime glassVickers indentation620658670conference paper