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The fatigue crack propagation characteristics of three steel alloys were evaluated at room and elevated temperatures in an air environment. The alloys and temperature ranges were: A212-B (σYS = 40 ksi) 75 to 800 F, A517-F (σYS = 104 ksi) 75 to 950 F, and 9Ni-4Co-0.30C (σYS = 185 ksi) 75 to 650 F. The compact tension specimen was used for the 9Ni-4Co-0.30C and A517-F tests. A modified compact tension specimen having deep face notches in the crack plane was used for the A212-B tests. Fracture mechanics parameters were used to evaluate the crack propagation data. When plotted as a function of the stress intensity range, ΔK, the crack growth rates increased with temperature in A517-F and A212-B; temperature did not influence the 9Ni-4Co-0.30C data. Tests at reduced cyclic frequencies were conducted on A517-F and 9Ni-4Co-0.30C steel. The crack growth rates increased as the frequency was reduced in A517-F at 500 and 950 F. In 9Ni-4Co-0.30C the growth rates at 500 and 650 F were essentially the same for cyclic frequencies of 10 and 0.002 Hz over the range of growth rates investigated.
fatigue (materials), crack propagation, alloy steels, yield strength, creep properties, plastic deformation
Project structures engineer, Convair Aerospace Division, General Dynamics, Fort Fort Worth, Tex.
Professor of metallurgy and materials science, Lehigh University, Bethlehem, Pa.