From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from a report on Wohler Fatigue Tests, detailing results for various specimens and discussing material properties.
| Identifier | ExFiles\Box 132\1\ scan0026 | |
| Date | 5th January 1938 guessed | |
| - 5 - Wohler Fatigue Tests. Specimen B .. 4.91 million reversals at 7 Tons per sq. inch. 0.22 " " " 8 " " " (Failed). " C .. 9.445 " " " 7 " " " " 4.74 " " " 7½ " " " " 10.82 " " " 8 " " " " 10.084 " " " 8¼ " " " " 7.102 " " " 8½ " " " " 1.091 " " " 9 " " " (Failed) " D .. 10.025 " " " 7 " " " " 5.006 " " " 7½ " " " " 1.46 " " " 8 " " " (Failed) " E .. 10.01 " " " 7½ " " " " 5.004 " " " 8 " " " " 0.648 " " " 8½ " " " (Failed) " F .. 0.343 " " " 7½ " " " (Failed) The amount of variation in the results between individual samples is not surprising with a non-ductile material like cast iron, but with the exception of Specimen C, the range is fairly small, and the failing stress being between 7½ and 8½ Tons per square inch. From the graph of the observations, the safe limiting stress would appear to be 7 Tons per square inch. In the case of crankshafts, the stressing is largely the result of mal-alignment or wear of bearings, and is, therefore, a function of the amount of distortion of the shaft rather than the appreciation of a definite bending moment. In the comparison of similar materials having the same Youngs' Modulus, the usual limiting fatigue stresses may be employed as the basis of comparison, but in the case of cast iron, where varying values of Youngs' Moduli are obtained, it may be better to base such comparison on the basis of their limiting fatigue distortions. This may be done by measuring both the limiting fatigue stress and the Youngs' Modulus, and when assessing the merits of the two materials to compare the ratio of these two properties, i.e. F/E.{Mr Elliott - Chief Engineer} | ||