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).
Guide on the painting of brittle lacquers and illustrations of their use in strain analysis.
Identifier | ExFiles\Box 142\2\ scan0472 | |
Date | 16th December 1939 guessed | |
5 gages are desired, the qualitative picture of areas and directions of principal strains provides a most excellent aid in the placing of the gages. Painting of Brittle Lacquers. All the apparatus we have found to be essential for this type of strain analysis are grouped in the cabinet in Figure 2. They are: spray gun, air regulator and calibrator on the upper shelf; psychrometer, calibration strips and their scale in the drawer; lacquers in the bottom tray and lacquer selection chart and psychrometer chart on the door. The brittle lacquers are best applied with a spray gun. Surprisingly, clouds of bubbles driven into the lacquer coating by the action of the gun not only cause no detrimental effect on the brittle properties of the coating, but aid materially in causing more uniform cracking. A bright surface beneath the brittle coating is essential for cracks to be visible. If the surface is not naturally reflecting, a specially prepared aluminium-pigmented under-coating lacquer is used. This provides a good reflecting surface and will dry sufficiently in thirty minutes to allow painting of the brittle lacquer. Illustrations of the Use of Brittle Coatings The growth of the crack patterns on a structure as the load is increased is always an educational picture to watch. In Figure 3 are given four stages during the loading in tension of a plate with a some-what elliptical hole. From the load and local strain data, the concentration factor of the hole is easily computed. A brass bar twisted in torsion shows in Figure 4 the principal tension strains as continuous cracks formed during loading. In addition the compression strains are shown by short cracks interspersed between the tension cracks and at right angles to them. These compression cracks were formed by the relaxation of the load after it had been held at its maximum value for an hour. Figure 5 illustrates the different straining of two welds of identical size and loading, but with one preformed so that the line of action of the two plates is a single straight line, while the other has eccentric lines of action. The eccentricity introduces bending into the welded joint on the right, materially increasing the amount of strain in the plate next to the weld. | ||