Fatigue crack monitoring in mild steel specimens using acoustic emission and digital image correlation

Acoustic emission (AE) is a passive form of non-destructive testing that relies on the detection of transient elastic waves released by localised sources within a material as it undergoes deformation. It is a highly sensitive technique for detecting processes such as plastic deformation and crack propagation. The aim of this investigation was to quantify AE in mild steel specimens and relate it to damage mechanisms. Digital image correlation (DIC), a full-field strain measurement technique, was used to characterise plastic deformation and crack growth. This paper investigates in detail the results of three 'dog-bone' style specimens undergoing uniaxial fatigue loading. AE was monitored in the tests, to allow both the detection and location of signals, and DIC images were captured periodically to provide a clear depiction of the surface strain field evolution. Located signals were compared with areas of high deformation and crack growth, as identified by the DIC system. Scanning electron microscope (SEM) fractography was used to investigate crack initiation and growth. The results demonstrate that the combination of AE and DIC can provide much useful information to help to distinguish the different AE signals originating from various possible failure mechanisms.