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).
Stress tests and modifications made to leaf springs to improve life and safety factor.
| Identifier | ExFiles\Box 154a\2\ scan0109 | |
| Date | 13th May 1939 | |
| -2- This calculation is based on the assumption that the spring is of ideal design and the stress therefore is uniform throughout. Further tests were carried out to determine the point of maximum stress on the top leaf. By means of a depth gauge the differences in curvature at different points on the leaf were measured. This was done for a variety of spring deflections. When running with 3" cams the bump rig imparts to the wheels a total movement of 7¼" - 3¾"-ve camber. The stresses due to this movement at six different points on the leaf, are plotted on the graph attached. Both the maximum stress and max. stress range occur approximately at the point on the leaf where we have had all our failures. Max. local stress is 86,000 lb/sq.in. Max. local stress range is 68,800 lb/sq.in. The max. local stress therefore is about 9,000 lb/sq.in. more than the average stress. As 25 sets of springs are already made for B.V. production we have decided to reduce the thickness of the main leaf and fit an extra leaf beneath it. This modification reduces the average maximum stress 6,000 lb/sq.in. and the stress range is proportionately decreased. We have tested two springs incorporating these modifications and the average length of life has increased from 14 hrs. to 20 hrs. this we consider satisfactory for production. Furthermore whereas on the previous springs the main leaf always failed first, on the modified springs secondary leaves failed first. As regards the remaining batch of springs ordered for production these will all have an extra leaf, making nine in all, resulting in a slight increase in weight coupled with a corresponding increase in safety factor. Rm {William Robotham - Chief Engineer} /FWK. | ||