ANALYSIS OF THE KINETICS AND DIRECTIONALITY OF ELASTOPLASTIC DEFORMATION AND FRACTURE

Abstract

Safety, survivability, and serviceability of the equipment are governed by the strength characteristics of the separate units and elements which can contain initial or operational defects such as superficial differently oriented semi-elliptical cracks. Numerical methods of calculation provide a large bulk of information about the stress-strain state (SSS) of those elements proceeding from the given algorithms for calculating the corresponding fracture models. Change in the type of the SSS near the crack contour when going from the bulk to the surface depends on the constraint of deformations along their front, i.e., on the 3D character of the SSS. Diagnostics of the form change of the defects (surface differently oriented semi-elliptic low-cycle cracks) is carried out on the basis of experimental results and numerical solutions. The data of the finite element modeling are implemented on the basis of macros of the ANSYS program complex. The regularity of the directionality of developing the elastoplastic fracture under low-cycle loading is studied. The proposed methodology is proved by the parametric equations of the kinetics of forming changes of the cracks under study in the fractographic analysis of the surfaces of their development. The results of testing samples with semi-elliptic cracks under low-cycle loading are used in analysis of the parameters of the morphology of the surfaces of the developed defects. The results of measuring fields of elastoplastic deformation intensity in the crack tip and geometrical characteristics of the fracture surface development are presented. Analysis of the dynamics of the local stress-strain state near the contour of multi-oriented defects in parts and structural units of the equipment showed a good agreement between the experimental parameters of the geometry of developing cracks and characteristics obtained by numerical methods. The presented parametric equations specify the characteristics of nonlinear fracture mechanics thus providing reliable estimation and forecasting of survivability, and safety of serviceability of the critical equipment. The deformation criteria of nonlinear fracture mechanics are used to demonstrate the dependence of fracture development on the 3D character of the stress-strain state indicating to the directionality of the geometric development of the fracture surface form.