Effect of load cyclicity on the fracture toughness characteristics of steels. Report 1

Abstract

1. We studied the effect of teat temperature on fracture toughness characteristics and features of stable and unstable fatigue crack growth in the static and cyclic loading of steels 15Kh2MFA and 15Kh2NMFA (I, II). 2. It was shown that a reduction in test temperature leads to a substantial reduction in the fracture toughness characteristics K fc 1 , K fc k , and kIc of the investigated steels under static and cyclic loadings. Under certain conditions, for several of the materials the cyclicity of the loading substantially lowers the fracture toughness characteristics. For the steels investigated, at 293 °K loading cyclicity negligibly changes K fc 1 compared to kc. At low temperatures, k fc 1 changes substantially compared to KIc. For a given test temperature, the values of K fc 1 at which loading cyclicity has a significant effect depends on the initial value of KI at the beginning of the test and on the number of load cycles. 3. The laws of unstable fatigue crack growth in steels 15Kh2MFA and 15Kh2NMFA (I, II) under cyclic loading (number and sizes of crack jumps) are determined by the test temperature, the level of initial values of KI in the test, and the ratios of the fracture toughness characteristics K fc 1 , K fc k , and kIc. 4. A reduction in the test temperature leads to an increase in resistance to fatigue crack growth at low values of kI and a decrease in resistance to fatigue crack growth at higher KI. 5. A reduction in loading frequency ambiguously affects resistance to fatigue crack growth for different materials.