Acoustic Emission Monitoring During Fatigue Crack Growth in Standard C(T) and Miniature Single Edge Notch Tension Specimens

The fatigue crack growth rate studies in a structural alloy has been carried out using ASTM E-647 standard compact tension (C(T)) specimens and miniature single edge notch tension specimens (SEN(T)) at two different stress ratios of 0.1 and 0.7. Standard C(T) specimen had a dimension of 63.5 × 61 × 8 mm thickness while the miniature SEN(T) specimen had a size of 20 mm effective length × 10 mm wide and 0.7 mm thickness. A starter notch of 0.5 mm was cut using wire EDM process to initiate fatigue crack growth in miniature SEN(T) specimen. A special fixture was designed for testing the miniature SEN(T) specimen. During the fatigue crack growth experiments, Acoustic Emission (AE) activity was monitored on-line using AE sensors from Physical Acoustics, Mistras Group, USA. For the experiments on standard C(T) specimens, a standard probe (R15A) of 15 mm diameter was used, while for small size compact tension specimen, a Nano30 AE probe was used. The crack growth was monitored by visual methods as well as by compliance technique. The cumulative counts and absolute energy information obtained during fatigue crack growth testing was used to correlate the crack growth rate with acoustic emission activity. Empirical fit of data was used to obtain cross-correlation between crack growth rate and AE parameters for both the specimen geometries. The study suggested that suitable selection and placement of sensors is essential to obtain good results using AE sensor technique.