Mathematical Model for Assessing the Limits of Crack Resistance of Structural Steels of Large-Sized Structures

Abstract

In metal structures under operating conditions, as well as in emergency situations due to overloads, the presence of stress concentrators, etc., plastic deformations may occur. Such deformation by tensile stresses introduces some damage to the structure of steel, which adversely affects its subsequent operation under cyclic loads. Preliminary relative plastic deformation, ∼ 1-6%, which occurs in structural steels under tension, unambiguously reduces plasticity. It negatively affects the endurance of the material and leads to the early formation of macrocracks. In addition, after unloading, an internal residual stress field at the meso-micro level remains in the structural elements, which also reduces the endurance limit. In causes the decrease of such an important indicator of reliability as fracture toughness, which reflects the resistance of the material to crack propagation. In this regard, designing structures, it seems important to improve the calculation methods for assessing and predicting their fatigue strength, taking into account the listed factors. The article is devoted to the development of a mathematical model that includes dependencies for assessing the fracture toughness of metal structures according to the fracture toughness limit for all sizes of defects in the form of cracks. Analytical dependences have been obtained for calculating the relative limit of crack resistance based on the main mechanical characteristics of the state of the material. The results of the study can be used to assess the crack resistance of structural elements and welded joints pre-deformed by tension.