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There can be no question about the decrease in design efficiency because of the use of ideal mechanical properties listed in the handbooks plus nebulous factors of safety based solely on experience. This practice imposes special difficulties for the younger engineers. Would it not be better to use factual strengths based on tests of specimens representing actual parts rather than the highly polished specimens? If the following factors are observed, handbook yield strengths and moduli of elasticity are ensured in cast, wrought, and welded parts: 1. Ensured hardness by testing the parts 100 percent if necessary. 2. No gross surface defects. 3. No crack-like defects that are improperly oriented in highly stressed areas. 4. Not more than 50 percent of the section removed by machining. If these four precautions are observed, proof will be offered that, if the stress concentration is kept under 1.5, design strengths for a typical “soft” steel can be increased from the present nominal 15,000 to 20,000 to 25,000 psi.
design criteria, safety factor, ferrous castings, gray iron castings, ductile iron castings, malleable iron castings, mechanical properties, metals, tests, evaluation
Caine, J. B.
Consultant, Grede Foundries Inc., Wyoming, Ohio