The T-stress influence on the plastic zone size around the crack tip under the thermal load

Abstract

A review of the fracture mechanics problems for estimating the safety of constructions with the crack-like defects is carried out. The need to develop a new methodology that combines the advantages of calculation and instrumental methods was revealed. The correlations between the most important fracture mechanics parameters and the characteristics of acoustic-emission signals proposed to use for estimating the parameters of stress-strain state. It is noted that considerable attention should be paid to the size and shape of the plastic zone in order to establish a theoretical relationship between the characteristics of acoustic signals and the fracture mechanics parameters. It is assumed that T-stresses are the cause of differences in the coefficients of the power dependence of the parameters of acoustic signals for the same values of the stress intensity factor. The task of finding the influence of T-stresses on the size of the plastic zone at the crack tip is set. A numerical modeling of thermal loading of a steel sheet with a central crack by the finite element method is carried out in order to determine the dependence of the crack tip plastic zone size on the stress intensity factor for several values of T-stress. Multiple calculations of the stress intensity factor and the T-stresses were performed for the several values of the cooling zone, using the parametric design language ANSYS APDL. By substituting the yield point of the material into the equations of linear elastic fracture mechanics, the specific volume and linear plastic zone size along the crack line were determined for the previously found values of the stress intensity factor and T-stress. A relationship between the fracture mechanics parameters and the plastic zone size at the crack tip was established using numerical methods. The assumptions that the T-stress influence to the plastic zone size are qualitatively confirmed. It is shown, that the negative values of T-stresses decrease the plastic zone size for a same value of the stress intensity factor.