Previsão da vida à fadiga das barras de aço CA 50 temperadas e revenidas por meio do modelo de Tanaka e Mura

Abstract

The phenomenon of fatigue is one of the main causes of damage to reinforced concrete bridges in the long time. In these structures, steel reinforcement bars are determinants of resistance when the concrete is in good condition. The aging of bridges associated with the increasing volume and traffic load, makes it essential to have a good understanding of the fatigue behavior of these elements. However, current methods for safety analysis of fatigue are based on conservative methodologies for new structures or on an incomplete knowledge of the performance of steel reinforcement bars. In this context, this research sought to contribute to the study of fatigue in tempered and tempered CA-50 steel reinforcement bars, one of the types of bars found in bridges. For this, was developed a 2D stochastic micromechanical model for predicting fatigue life, based on the Tanaka and Mura initiation model for metallic components. In the model, only the crack initiation phase was considered. As the initiation phase can consume a significant part of life due to fatigue, aspects of the microstructure, such as phase, geometry and orientation of the grains were considered, as well as the coalescence of the microcracks. The Finite Element Method was used to evaluate the stress field in the grains during the initiation and propagation of microcracks. The simulations were carried out for three bar geometries. The crack propagation, at the microstructural level, was considered along sliding bands and depending on the accumulated strain energy, the loading and the surface energy of the microstructure. The results showed that the proposed model was able to describe the initiation and propagation of microcracks in steel reinforcement bars with good agreement with experimental results in the literature. The model was also able to predict the fatigue life of tempered and tempered bars in the regime of high fatigue cycles and experimental dispersion.