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).
Laboratory report on the failure analysis of a Wraith fan blade.
| Identifier | ExFiles\Box 83\2\ scan0144 | |
| Date | 16th November 1937 | |
| Rm{William Robotham - Chief Engineer}/Std. H1/EJW.7/JH.16.11.37. M.1458. LABORATORY. WRAITH FAN EW.947 USED ON 6.B.IV. Your ref. Rm{William Robotham - Chief Engineer}/Std.7/JH.15.11.37. One blade of this fan was broken off and another cracked, in each case at the end of the pressed "buttress" - see photo. M.1458/1. (5305.S). Several unused fans were also examined. All were formed in handmade dies which had rather sharpe edges. This had resulted in the metal being strained at the edges of the raised part of the blades. In the broken fan the strained part had been filed and the ends of the file cuts were on the twisted part of the blade close to the raised part. Cracks were found running along these file scratches - see photo. M.1458/2. Micro-examination showed that the temperature employed when twisting the blades (described as a red heat) had not resulted in an increase in grain size in either the broken fan or the unused one. The carbide was mostly segregated in the cell walls but fracture tests did not suggest brittleness, and a close bend test did not produce cracks. Analysis confirmed that the material was not to specification 2S9.A. The composition conformed to the requirements of the specification 202.A. Apart from the wrong material having been used the design itself appears to concentrate the stress at the end of the raised part by reason of the twist in the blade terminating at that point. The file scratches therefore are probably no more than a contributing factor in the failure. ENCLOSURE No 530 H1/E.J.V. | ||