Damage Induced by a Spherical Indentation Test in Tool Steels Detected by Using Acoustic Emission Technique

The aim of this study is to monitor the subsurface damage mechanisms of commercial cold-work tool steel by observing acoustic emissions generated in a spherical indentation test. Monotonic loads are applied in the elastic and plastic ranges to damage the specimen. Two types of damage prior to the occurrence of cracking are found: carbide breakage and plastic deformation. The phenomena are confirmed by microscopic images and the good agreement between the estimated carbide fracture strength and previous results. The two types of damage gives rise to different acoustic emission signals: a burst-type, high-amplitude signal for the breakage of carbides and a continuous-type, low-amplitude signal for plastic deformation. It is thus possible to detect and differentiate the incipient damage mechanisms on the subsurface in real time in a spherical indentation test.