Evolution of damage accumulation in low-carbon steel in tension condition

Abstract

Stages of damage accumulation process in notched specimens from low-carbon steel at tension were studied by means of replicas, acoustic emission and ultrasound attenuation methods. The shape and size of plastic deformation zones at a pre-existing crack tip, microcrack length and density in the zones were estimated and cumulative distributions of microcracks by their size were obtained. Acoustic emission method was used to control the damage accumulation process at various stages of loading in a real-time mode. Acoustic emission sources recorded during the loading of the specimens were located and the cumulative amplitude distributions of acoustic signals were estimated. It was established that cumulative distributions of microcracks and acoustic emission signals on initial stage of damage accumulation are well described by an exponential function which is replaced by a power law one at a load close to the maximum value. At this stage of loading, density of microcracks and acoustic emission signals approaches a limit value, crack coalescence leading to the main crack formation begins and ultrasound attenuation coefficient sharply increases. The results obtained are compared to the pattern of crack accumulation in rocks.