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The distribution of residual stress in square phenolic bars was determined from the deformations resulting when (a) one face was milled to various depths and (b) holes of increasing diameter were bored longitudinally. The techniques resembled those in use with metals except that some of the deformations were measured with electric strain gages for high sensitivity and the equation for the milling method was considerably simplified. With fillers of wood flour and chopped fabric, the stresses were under 1000 psi except near the surface of the bar where they reached as high as 3000 psi compression. With a rapid qualitative method it was found that variations in the method of molding have little influence on residual stresses in a composition of phenolic resin and wood flour. The flexural strength of a phenolic bar may depend on the residual stresses present, but the connection is difficult to analyze. A complicating factor is that the true strength of the material may vary over the cross-section.
Welch, L. E.
Professional Engineer, Glen Ridge, N. J.
Quackenbos, H. M.
Bakelite Co., a Division of Union Carbide and Carbon Corp., Bound Brook, N. J.