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The fatigue behavior of several steels, AISI 4130, E52100, and 304 ELC stainless, as well as that of a nonferrous alloy, 5456-H311, was investigated in rotating bending fatigue after these materials were subjected to a prestress for different cyclic histories. The data obtained corroborated the hypothesis proposed by the authors that lines representing the S - log N relation of a material prestressed in varying amounts will intersect the S - log N line of the original material near a common point. A correlation was found between the stress at this intersection point and the ultimate tensile strength. Thus, the only requirements for establishing the fatigue behavior of a prestressed material in the range of stresses where the S -log N line is inclined are the S - log N line of the original material and the ultimate tensile strength. The importance of determining the new endurance limit of a material after prestressing was shown analytically.

The high-temperature capability and workability of cobalt-tungsten alloys for aerospace applications is discussed. The average life at 1850 F and 15,000 psi of the strongest previously reported alloy Co-25W-1Ti-1Zr-0.4C was doubled from 92 to 185 hr by small additions of chromium and rhenium. At 2200 F and 5000 psi the strongest alloy, Co-25W-1Ti-1Zr-3Cr-2Re-0.4C, had a rupture life of 23 hr; the elevated temperature rupture strength compared favorably with the strongest available conventional (high chromium) cobalt-base alloys. It is particularly significant that even the strongest alloys of this series were readily hot-rolled. Elongations as high as 31% were obtained at room temperature with annealed cold-rolled sheet specimens. The good ductility obtained suggests that these alloys could be fabricated into complex shapes required for various aerospace and other applications.

A nickel-base alloy, TAZ-8B, has been developed which compares favorably in high temperature strength with known high strength nickel-base alloys. Although basically a cast material, the alloy also possesses workability potential. By applying directional solidification techniques, test specimens were produced with a preferred columnar grain orientation. Grain boundaries transverse to the major stress axis were largely eliminated. Substantial increases in ductility, ultimate tensile strength, and stress-rupture life were obtained with the alloy in the directional polycrystalline condition as compared to the random polycrystalline condition. For example, the 1400 F ductility, which was 3% in the random polycrystalline form, was increased to 6% in the directional polycrystalline form. Ultimate tensile strength was similarly raised from 144,000 to 172,000 psi at this temperature.