THIRD PROGRESS REPORT TO MATERIALS LABORATORY WRIGHT AIR DEVELOPMENT DIVISION ON EFFECT OF PRIOR CREEP ON MECHANICAL PROPERTIES OF AIRCRAFT STRUCTURAL MATERIALS. Period covered: October 1, 1959 to December 31, 1959

Work accomplished on the Rene 41 alloy included determination of exposure, the effects at 100/hr at 1400, 1600, and 1800 deg F without stress, and under stresses yielding creep deformations of approximately 1% under the same conditions on room temperature tensile properties. Creepexposure tests of the 80 Ni--20 Cr alloy were conducted for 5 or 50 hours at 1000 to 1800 deg F on small- and largegrain materials. Tensile tests at room temperature indicated that the large-grain material exhibited greater increase in strength and smaller decrease in ductility than the small-grain material after prior strain at either room temperature or elevated temperature. Creep exposure for longer than 50 hr at 1800 deg F resulted in extensive surface cracking and negligible ductility in subsequent tensile tests. (For preceding period see NP-8767.) (J.R.D.)