Cermet turbine blades were made with the root centerline curved to approximate the camber of the airfoil; the design eliminates any over-hang between the root and the airfoil. This change eliminated the need for the blade platform and thus reduced the effective tensile stress in the blade root 20 to 30 percent and the nominal tensile stress in the root component of the rotor about 22 percent.nThe blades were tested in a full-scale jet engine at an estimated blade temperature of 1500° F. In five engine tests, minimum life at rated speed was 77 hours; this blade failed in the airfoil. The short¬est life terminated by root failure was 143 hours, which indicates in¬creased strength and reliability of the root. In the longest run, oper¬ation was arbitrarily discontinued after 150 hours with no failure of the cermet blades.
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