Acoustic emission, damage and fracture mechanisms of structural steel under mixed-mode loading

Mechanical and acoustic properties, damage kinetics and fracture mechanisms of 30CrMnSiA structural steel under mixed loading modes (I + II) have been investigated. It is shown that the change in loading mode leads to changes in strength and acoustic parameters, microcrack accumulation kinetics and fracture mechanism. The greatest changes in average frequency (AF) and rise angle (RA) of acoustic emission signal with increase in load are observed when the sample is oriented at an angle of 15°, at which the AF decreases linearly depending on the average values of the signal RA. However, the acoustic emission characteristics are not only determined by the loading mode but also by the fracture mechanism: brittle fracture at an angle of 45° is accompanied by increase in many acoustic characteristics including RA and AF parameters and a change in the type of time dependence of the total number of acoustic signals (ΣNAE), bAE – value and cumulative energy of acoustic emission signals (∑EAE). The frequency analysis showed that the average values of the peak frequency and the frequency centroid at rupture exceed the values of these parameters under mixed loading modes. A change in the failure mechanism under mixed loading modes does not affect these acoustic characteristics. Analysis of the kinetics of microcrack accumulation showed that the rate of damage accumulation decreases as the shear component of the load increases.