RESEARCH ON CUMULATIVE FATIGUE DAMAGE OF AIRCRAFT STRUCTURAL MATERIALS.
Progress rept. no. 9,
COLUMBIA UNIV NEW YORK DEPT OF CIVIL ENGINEERING AND ENGINEERING MECHANICS
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Tests for the establishment of an S-N diagram for SAE 4340 steel have been completed and their results are presented in Table I. Statistical evaluation of the data and plotting of curves will be carried out as has been done previously for aluminum. Three sets of random tests have been completed using the least severe load distributions A, B, C. The results are presented in Table II. Since the longest lives obtained in the tests were in the 50,000 cycles range, the advisability of running more severe tests is being considered. A revision of the load distributions will probably be made. An attempt was made to perform systematic test on AA7075 Aluminum and SAE 4340 steel submerged in water. A small 1 in long piece of rubber tubing with an internal diameter of 14 in is fitted around the reduced 316 in section of specimens, and sealed at the ends. Water is injected with a hypodermic needle. Several preliminary tests were performed using this procedure. The results suggest a considerable reduction in life for both aluminum and steel.