Acoustic emission applications for defect detection in steels and GFRP: International Journal of Materials and Product Technology, Vol. 3, No. 1, pp. 38–53 (1988)

An acoustic emission (AE) technique has been applied to detect, locate and recognize some kind of defect in GFRP and in welded stainless steel thin plates. In these cases, if many AE parameters such as peak amplitude, count rate, energy rate, Felicity ratio, and other new parameters (RA and RI) are recorded and compared, it is possible to know with good accuracy and reliability the type of defect which is present. Detected defects in GFRP are curing errors, holes, impact damage, delaminations, fatigue damage and humidity. Detected defects in TIG welded stainless steel are various size and shape tungsten inclusions and notches. In this case an 'Expert System' running on a personal computer has been developed to obtain an automated diagnosis. A further AE application concerns the fracture toughness measurement of some steels. In this application AE is able to detect the first stable crack propagation during a single–specimen JIC, test. In brittle steels, results obtained are very close to JIC values measured by the four–specimen method. In the case of a high–toughness NiCrMoV steel, AE also seems able to detect, in 25–mm thick specimens, a first 'pop–in', normally otherwise evident in 125–150–mm thick specimens only.