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).
Paper on the use of brittle lacquers as an experimental method for stress and strain distribution analysis.
| Identifier | ExFiles\Box 142\2\ scan0468 | |
| Date | 14th March 1940 guessed | |
| BRITTLE LACQUERS AS AN AID TO STRESS ANALYSIS by A.{Mr Adams} V.{VIENNA} de Forest and Greer Ellis Abstract The fracturing of brittle coatings has long been recognized as an experimental method of checking strain distribution. Flaking of brittle mill scale at the yield point of local areas was used in the testing of the first wrought-iron bridges. More recently brittle resin coatings which will fracture the elastic range of most materials have been developed to give good qualitative pictures of strain distributions. The present work describes an improved brittle coating in the form of a sprayable lacquer which air-dries overnight to form a coating of uniform brittleness within the limits of thickness of three to eight thousandths of an inch. A calibration method is described whereby quantitative values of strain may be estimated within a fifteen percent error. Introduction Engineering structures are designed to transmit loads. The basis of the design is two sets of assumptions. One, the estimation of the loads to be carried; the other, the manner in which these loads flow through the structure. From consideration of the assumption of distribution the shape and materials of the design are derived. The primary role of stress analysis is to check a design for the distribution of the forces being carried. In many cases a number of alternative designs are available and the best or the cheapest is to be selected. To aid in this check, loads, simulating service conditions, often are applied to the structure and strains measured over the critical areas. Convenient mechanical or optical strain gages can be used down to about one-half inch gage length, but cannot be readily applied to fillets, curved surfaces and inaccessible regions. They are further handicapped by the number of separate measurements that must be made at different points and different directions in order to be reasonably certain that the most critical strains have been located. The perfect strain gage might be thought of as one which would simultaneously give an infinite number of readings of infinitesimal gage length over the entire surface of the structure. Brittle coatings under proper control can | ||