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).
Comparison of the fatigue properties of cast iron and steel, followed by crankshaft experiment details.
| Identifier | ExFiles\Box 132\1\ scan0019 | |
| Date | 18th April 1927 guessed | |
| - 6 - For the cast iron under consideration, the limiting fatigue stress is approximately 7 Tons per square inch, and the Youngs' Modulus 17.68 x 10^6 lbs. per square inch. Comparing this material with a typical steel of limiting fatigue stress 20 Tons per square inch, and Youngs' Modulus 30 x 10^6 lbs. per square inch, we have:- Ratio of limiting fatigue distortion:- Steel 20 / (30 x 10^6) Cast Iron 7 / (17.68 x 10^6) = 1.68. Ratio of limiting fatigue stresses:- Steel 20 Cast Iron 7 = 2.86 The first comparison shows the cast iron in a much more favourable light than is obtained by the second comparison. CRANKSHAFT EXPERIMENTS. Following the assumption that the stressing of crankshafts is largely the result of mal-alignment or wear of the bearings, a test was carried out with a cast crankshaft of similar composition, against the standard stamped steel crankshaft. A four-cylinder petrol engine was used for the test, and a rig arranged which permitted of a mis-alignment of the centre main bearing, the deflection of which could be measured. The crankshafts were mounted in three main bearings and it was found after some preliminary experiments that if the main centre bearing was deflected 0.030" out of alignment sufficient stress could be set up in the crankshaft to produce fatigue failure. Three crankshafts were tested, two were to a standard steel specification, and one made of alloy cast iron, of similar composition to the test pieces from which the fatigue resistance determinations | ||