NACA-RM-53L22

Abstract

Additional static and fatigue tests were made on aluminum-alloy 355-T6 sand-cast specimens. Direct-stress fatigue tests were made on plate-type specimens with a single l-inch-diameter as-cast cored hole and on specimens in which the cored hole was reamed to 1¹/₁₆-inch diameter. In addition, direct-stress fatigue tests were made on 0.300-inch-diameter specimens, with various degrees of porosity, machined from the butt ends of plate-type specimens. Comparisons are made with the results of earlier tests, on plate-type specimens with variations in design details such as bosses and ribs, given in NACA Technical Note 2394. <br>Within the range of stresses used, there were no significant differences in the fatigue strengths of sand-cast specimens with a l-inch-diameter cored hole when tested with the hole in the as-cast condition or with the hole enlarged l/16 of an inch in diameter by reaming. When the results of tests on the specimens with a l-inch-diameter cored hole are compared with results, from the previous investigation, for specimens in which a small cast boss was removed and a l-inch-diameter hole drilled and reamed in the center of the plate-type specimen there is found to be no significant difference in the results except for a slight difference in the static strengths.