An <i>In Situ</i> Three-Point Bending Study on Pre-Notch 7075 Aluminium Alloy with Acoustic Emission

Abstract

Some types of congenital and machining-induced defects remain in a material, such as cracks and crack notches generated in a series of machining processes. Such structural defects will probably lead a reduction in the material's service life, and even a huge accident. It is important to investigate the influence of crack initiation, crack growth and crack failure in relation to the downgrading and failure of materials. We have employed the acoustic emission (AE) signal to identify the 7075 Aluminium alloy (7075 Al) crack initiation and crack growth unilateral precrack, bilateral pre-cracks, unilateral V notch and bilateral V notches under three-point bending (TPB) conditions. At the same time the tip morphology of notch specimens is obtained by the opto-digital microscope. Comparing the in situ images with the AE signals, the results indicate that the AE signals can effectively predict the crack initiation, crack growth and crack rapid instability during TPB test. In addition, the geometrical shape of the specimen is relative to the intensity of AE signals. The AE signal of a no notch specimen is much higher than that of other notch specimens. The intensity of the AE signal of pre-crack specimens is lower than the V notch specimens. A pre-crack specimen causes failure more easily than the V notch specimen in the process of bending. Specimens with no notch, unilateral pre-crack, bilateral pre-cracks, unilateral V notch and bilateral V notches can be characterized by the intensity of AE signals. The position of the crack can be determined by the linear position of the AE signals.