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).
Analysis of spring specimen fractures and failures, referencing photomicrographs and various test results.
| Identifier | ExFiles\Box 95\3\ scan0170 | |
| Date | 20th June 1935 guessed | |
| -2- In this connection the two photomicrographs Nos. A1,329 and A,1330, X3, will be of interest. These show two fractures, and on the right hand side of each a similar, though smaller, "lip" will be noticed. No. A1,329 is of a three-inch specimen cut from the spring and broken in a hand-press. No. A1,330 is of a similar specimen, but in this instance a deep circumferential groove was ground in the rod to reduce its diameter from 0.694" to approx. 0.600". The specimen fractured at the bottom of this groove, and although the grinding must have removed any decarburised layer, this did not prevent the production of the "lip". Photomicrograph No. A1,331, X3 shows what we consider to be the starting point of the break. It will be observed that there is no "lip" here, but that the fracture is of the smooth fatigue type with a definite centre at the point indicated by the arrow. Photomicrograph No. A1,332, X3, of the same specimen from another angle, shows that this starting point of the fracture lies at the bottom of one of a series of surface flaws. These marks, when examined at a higher magnification, appear to be caused by some gripping tool, being similar to vice marks. They are not the marks shown in A1,328, which are due to grooves or cuts in the surface. Hs{Lord Ernest Hives - Chair}/Les.{Ivan A. Leslie} tells us that the spring failed on bumper test after 23 hours, and that the drawing quotes a stress of 145,000 lbs/sq.in. The failure appears to be directly analogous to the failures of highly stressed valve springs from small surface flaws which we have dealt with in previous reports. Another point which might be considered is whether the Brinell hardness is the most suitable for a spring of this thickness. When attempts have been made to produce a thicker leaf for a road spring, it was found that best surface was given the hardness, as compared with a thinner leaf, was reduced. For example, dropping the figure from 430 to 400 was found to be an advantage with a thicker leaf. HL. HE Photomicrographs Nos. A1,328-32 att. Photograph of complete spring - Ref.2479c. | ||