Estimation of the periods of initiation and propagation of creep-fatigue cracks in thin-walled structural elements

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

“…We solve this problem on the basis of the computational model proposed in [1] for finding the period of initiation of fatigue cracks at high temperatures. It is assumed that the plastic (process) zone formed near the tip of the concentrator under the action of applied loads p plays the role of the site of initiation of a creep-fatigue macrocrack (Fig.…”

“…At the same time, in view of the results presented in [1,5], we can assume that the initiation of a creepfatigue crack runs permanently from the zero length and is characterized by a variable rate V , which is a function of the maximal tensile strain ε max in a cycle in the process zone, i.e.,…”

“…By analogy with [1,5], we assume that the rate of initiation of a crack of length l is the same as the rate of its propagation for the same maximal strain amplitude ε max in the process zone. In view of these considerations and the results presented in [1], we write the following equation for the rate V of macrocrack initiation:…”

“…In view of these considerations and the results presented in [1], we write the following equation for the rate V of macrocrack initiation:…”

“…Here, α 0 is an experimentally determined constant [1], R is the load ratio, δ t max is the maximal crack-tip opening displacement δ t in a cycle under the mean stress σ t in the process zone, δ th is the lower threshold value of the crack-tip opening displacement δ t below which there is no creep-fatigue fracture, δ fC is the critical value of the opening displacement δ t , t 1 is an experimentally determined constant of high-temperature creep, t * is the period of holding in a cycle, t 0 = 1 h, and ! δ Ht max (0, C H ) is the opening rate at the tip of an incipient crack under the conditions of high-temperature creep in hydrogen-containing media in the process zone.…”