LOW-CYCLE FATIGUE CHARACTERISTICS OF ULTRAHIGH-STRENGTH STEELS.
FRANKFORD ARSENAL PHILADELPHIA PA
Pagination or Media Count:
Crack growth studies, using D6Ac steel, heat treated to 240,000 psi yield strength level, are described. In these studies the crack tip driving force was held constant for each cycle. Plate thicknesses of 0.160 and 0.075 inch were investigated in this study. In the thick plate behavior, which is exemplified by the 0.160 inch specimens, the plate thickness is substantially larger than the local plastic zone size at the advancing tip of the crack. The elastic constraint, therefore, dominates the rate of crack propagation. Because of the lower elastic constraint present in a 45 degree oblique shear fracture, the rate of crack propagation at a constant driving force is less than that for the cup-cone condition. In the thin plate behavior, the shear displacement on the y axis dominates, rather than the elastic constraint. The 45 degree oblique shear type of fracture, therefore, results in a greater rate of crack extension because the vertical displacements are larger than for the cup-cone type of fracture. Author