The Static and Low Cycle Fatigue Strength of Notched and Fatigue-Cracked Specimens of Low Alloy Steels

Abstract

Two kinds of low alloy steel of about 100kg/mmmm2 in tensile strength were put to tests: their specimens, notched and unnotched respectively as well as fatigue cracked, to the fatigue test of low pulsation cycle of tensile, and their fatigue cracked specimens in the range of 16 to 60mm in diameter to the static tensile test. The results of the tests are given as follows.(1) The fatigue strength of the unnotched specimens scarcely drops lower than their tensile strength till the pulsation of 104 cycles is reached, whereas of the specimens, both notched and cracked, the static strength, though higher than their tensile strength, decreases linearly with increasing number of pulsation cycles.(2) Fatigue strength of notched specimens after inititating crack on notch root coincides with that of fatigue cracked specimen.(3) Critical stress intensity factor KIC is constant independently of apecimen size and crack depth, when the external diameter of specimens is above 25mm.(4) Thefi nal fracture of low cycle fatigue occurs in the fatigue cracked specimens, within the diameter range of constant KIC, when their stress intensity factor KI reaches KIC. But when the diameter of are below this range the fracture condition of the low cycle fatigue does not coincide mechanically with that of Fracture Mechanics.