Influence of Hydrogen on the Initiation of Creep-Fatigue Cracks in Plates Near Stress Concentrators

Abstract

We formulate a mathematical model for the determination of the effect of hydrogen on the period of initiation of creep-fatigue macrocrack in the vicinity of a stress concentrator in a plate. By using this model, we find the period of initiation of a macrocrack for a strip with two side notches under cyclic loads, high temperatures, and the action of hydrogen-containing medium. It is shown that hydrogen increases the rate of crack initiation in steel plates.Keywords: hydrogen-containing medium, period of the initiation of a creep-fatigue macrocrack, stress concentrator, stress intensity factor.In the experimental and theoretical investigations of the creep-fatigue fracture of materials and structural elements [1−4], the attention of the researchers is mainly focused on the subcritical growth of creep-fatigue cracks. However, for flawless materials, a significant part of the service life of structural elements is covered by the period of crack initiation. Moreover, there are cases where the life of structural elements under high loads contains solely the period of initiation of creep-fatigue cracks.At present, there are numerous mathematical models, methods, and criteria for the evaluation of the period of crack initiation in structural elements under the conditions of fatigue and fatigue combined with creep [1, 5]. However, numerous structural elements operate under the influence of hydrogen, which facilitates the initiation and propagation of fatigue cracks and, hence, decreases their durability. Therefore, the investigation of the influence of hydrogen on the initiation of defects (cracks) in metallic materials and structural elements is an urgent problem today. Up to now, this problem has been investigated quite poorly. Hence, in the present work, we propose a computational model aimed at the description of the initiation of creep-fatigue cracks in plates with stress concentrators under the action of hydrogen-containing media. Formulation of the Mathematical ModelConsider a structural element (plate) weakened by a notch with radius of rounding at the vertex equal to r (Fig. 1) and subjected to cyclic loading with times of holding t * and the action of a high-temperature field T (the temperature of this structural element is higher than a half of the melting point of its material, i.e., T > 0.5T mp ), which induces high-temperature creep in the process zone.