Kinetics of the multidirectionality of elastic-plastic fracture with allowance for anisotropy of the material properties

Abstract

Survivability, service life and operational safety of the engineering structures are determined by their damage rate which is mainly regulated by the presence and development of the crack-like defects in the material. Kinetic dependences describing the development of multidirectional semi-elliptic surface cracks with allowance for the anisotropy of the material properties are proposed proceeding from experimental data and numerical solutions. The obtained results are required in studying kinematic problems in nonlinear mechanics of a continuous anisotropic medium. Refining parametric equations for elastoplastic deformation anisotropy are proposed. Functional dependences of the parameters of the kinetic diagrams of low-cycle fracture on the mechanical properties of the material are presented for a wide class of welded joints of austenite stainless cyclically stable steels (12Kh18N10T). The processes of developing inclined semi-elliptic surface cracks in the continuums of welded joints under non-linear boundary loading conditions are studied. We have carried out combined computational, experimental and numerical studies of the stress-strain state in the vicinity of the contour of stationary and growing surface semi-elliptic cracks randomly oriented in space under elastoplastic nominal cyclic loading taking into account the anisotropy of the material properties. The functional distribution of the inhomogeneity parameter of the mechanical properties of the material, which affects accumulation of the local plastic strains and direction of developing the elastoplastic fracture is obtained and presented in the form of the kinetic equation of nonlinear fracture mechanics. Comparison of the experimental results and numerical calculations of the stress-strain state along the contour of the cracks under study in nonlinear boundary loading conditions revealed a good agreement between the intensities of relative elastoplastic deformations at their surface points with allowance for the deformation anisotropy. Calculations of the elastoplastic fracture resistance of the critical elements of the equipment with allowance for considered factors of nonlinear fracture mechanics and heterogeneity of the properties can improve the accuracy of evaluation of their strength, service life and survivability.