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The objectives and limitations of the proposed recommended practice for determining sharp-notch strength of high-strength sheet materials are given. Two specimen designs are used: 3 in. wide with sharply machined edge notches, and 3 in. wide with a center slot extended in both directions by fatigue cracking. Evaluation test results are reported for sharp-notch strength of four materials: aluminum alloy 7075-T651, titanium alloy 4Al-3Mo-1V, maraging steel 18Ni-9Co-5Mo, and precipitation-hardening stainless steel PH 14-8 Mo.
Test data from seven laboratories are analyzed for differences among laboratories and between the two specimen designs. Agreement among laboratories is generally satisfactory considering inherent difficulties in preparing sharply notched specimens to the close tolerances required. Data from specimens out of tolerance after machining or after fatigue cracking were rejected. Center-cracked specimens have significantly higher sharp-notch strengths than edge-notched specimens in tests on the aluminum alloy and the precipitation-hardening stainless steel.
Test specimens 8 in. long are suggested as alternates for the recommended 12-in. long specimens when insufficient material is available. Significant differences in test results were obtained for the two lengths of specimens.
Supervising research metallurgist, Armco Steel Corp., Middletown, Ohio