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).
Technical discussion on magnification factor at resonance, with formulas for stress and amplitude in crankshafts.
| Identifier | ExFiles\Box 124\2\ scan0297 | |
| Date | 17th February 1941 | |
| Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}4/EP.{G. Eric Platford - Chief Quality Engineer}17.2.41. - 2 - Moreover we were concerned mainly with comparing two engines and providing a fair basis for comparison was used. Actual quantities did not appear to matter so much. For magnification factor at resonance it was therefore decided to use the expression M = A / √f₀ where A is a constant depending upon the hysteresis of the shaft and f₀ is the equilibrium stress in the shaft. This expression is deduced by Ker Wilson (Torsional Vibration Problems p.233) from values of the hysteresis constants and exponents given in Dr. Dorey's paper on 'Elastic Hysteresis in Crankshaft Steels', Proc.I. Mech.E 1932. A value A = 1250 was used. This is actually the figure given by Dorey for 3% nickel steels. Ker Wilson claims that, although not in strict agreement with the results of Dorey's investigation the expression can be used without much error. Its outstanding advantage is that it is easy to manipulate. In passing we should point out that in Rm{William Robotham - Chief Engineer}/JES.10/JH.13.2.39, the actual amplitude measured on a B.60 engine at 4500 R.P.M. full throttle with no damper was given as 1.4°. This compares with 1.5° given on sheet 4 of the memo under discussion. You state in your memo αs = Mα₀ We say that M = A / √f₀ Now f₀ is the stress at the node corresponding to the equilibrium amplitude and is therefore equal to fα₀. where f is the stress at the node for unit deflection of the free end of the shaft. Therefore M = A / √fα₀ and αs = (Aα₀ / √fα₀) = constant x √α₀ Equilibrium amplitude α₀, we agree is equal to Tₙ Σα / ω²ΣIα² | ||