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).
Findings from the 'Dynamic Fatigue Life of Rubber' paper from U.S. Rubber.
| Identifier | ExFiles\Box 178\2\ img012 | |
| Date | 25th April 1940 | |
| Serial No. 103 67 OY 6/D/Apr.25.40 April 25, 1940 Rolls-Royce, Ltd. Derby, England U.S. Rubber April 18, 1940 Rm.{William Robotham - Chief Engineer} Mr. Sloman, Drs. Yost, Merrill, Walter Keyes. 1) Attached are two copies of "Dynamic Fatigue Life of Rubber", a paper generally similar to the A.S.T.M. paper already reported to you. Dr. Yost told us that the extraordinary increase in fatigue life under high mean stress is explainable by X-ray examination of the rubber. There is ample evidence of an extreme orientation of the structure of the material to adapt itself to the load. Note also that my sketch of Serial No. 42 is not correct. The base line of the chart is percent minimum extension instead of percent mean extension as I stated. Zero minimum extension, i.e. when the rubber goes slack at the end of the stroke, appears to be about the worst condition. Dr. Yost said these results could not be explained away by the change in rate causing less work-storage at high extensions. The rate does decrease at first as the rubber is extended, but not nearly enough to account for the chart. Neither can the results be explained by change of temperature. The temperature line drops all the way from left to right of the charts, Figs. 7 and 8. The criticism that they were not testing through a more or less constant stress range is answered by Fig. 5 (center). The criticism that size and proportions of specimens may change results completely is answered to some extent at least by the pictures of test specimens in Fig. 4. The U.S. boys seem to be on the trail of something important and are keeping after it. Its usefulness to us does not start really until we get to such things as rubber front and rear | ||