COMPARATIVE ANALYSIS OF THE CRACKING RATE FOR A STAINLESS STEEL LOADED AT 213K TEMPERATURE

Abstract

The existance of a variable (cyclic) loading over a part or an subassembly may lead to the crack appearance in its body. The crack will spread unit it will reach a critical length leading to the instant specimen fracture. An important parameter that can control the fatigue fracture is the crack propagation rate marked as da/dN. This is the advancing length of the crack in a loading cycle. There were proposed, by various scientists from the researching field, many empiric relations, that have resulted from the experiments, that follow the fatigue fracture phenomena. In this paper a comparative analysis of the cracking speed will be made by using three mathematical models: Paris formula, Walker relation and Donahue relation. The experiments were made on CT specimens, with side notch, from a stainless steel 10TiNiCr175 type. The loading temperature was 213K (meaning -60C), and the loading was made for three types of asymmetry factors: R=0.1, R=0.3 and R=0.5. During the loadings, some primal quantities were take into account: the variation of the cracking length ai and the corresponding cycles number Ni. With these values there was calculated the variation of an important parameter in the Fracture Mechanics, ΔK– the stress intensity factor , and respectively the crack growth rate da/dN by polynomial method and the three presented models. With the obtained models some graphics were drawn representing the da/dN parameter variation and there were made comparisons between the four used formulas.