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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).
Stress testing a wheel rim using stresscoat lacquer to analyze compressive and tensile stresses.

Identifier  ExFiles\Box 96\4\  scan0174
Date  29th June 1939
  
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HPS{Horace Percy Smith - Experimental Factory Mgr}/B1.1/CB.29.6.39.

In order to test for compressive stresses in addition to tensile stresses, the wheel rim and a specimen strip were coated with stresscoat lacquer 666, whilst the tyre was under a pressure of 100 lb./sq. in. and left to dry for about 16 hours. When the lacquer was dry, the pressure was checked and found to have dropped to 95 lb./sq. in. The pressure was then reduced gradually but fairly quickly, and at 40 lb./sq. in. a full crack pattern had formed in the area marked "B" (BL.2357, Sheets 1 & 2). At 20 lb./sq. in. full crack patterns were also observed in the areas "C" & "D", and at 15 lb./sq. in. in the area "E" (BL.2357, Sheets 1 & 2). The cracks at "B", "C" and "D" were circumferential ones and those at "E" radial.

In order to determine the cracking strain of the lacquer, direct loading tests were carried out on the specimen strips. In each case it was found that cracks commenced at a strain of about 1.100 x 10-3 and that full crack patterns formed at an approximate strain of 1.400 x 10-3.

This rather high value is probably due to the fact that the temperature and humidity conditions during the drying period were not completely controllable.

Values of the stresses in various parts of the wheel rim under the normal tyre pressure of 35 lb./sq. in. based on the above results and allowing for the 20% possible error quoted by the manufacturers of Stresscoat Lacquer are shown in BL.2357, Sheets 1 & 2.

HPS{Horace Percy Smith - Experimental Factory Mgr}/W.Bell.

J.{Mr Johnson W.M.} Bromilow.
  
  


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