The Use of Plumber's Resin to Determine the Occurrence of Yield

Brittle lacquers used for the determination of elastic stress have a number of disadvantages, particularly in connexion with the technique of applying them and the need for careful calibration in each case. They are not generally applicable to the whole of very large specimens such as bridges.

Plumber's resin provides much the same information more readily and needs only a simple technique. It has, however, the disadvantage that it is necessary to stress the specimen slightly beyond the yield point. The technique of applying it, which is described in detail, consists in little more than the essential point that the resin must be applied hot without the use of a solvent.

After the specimen has been stressed beyond the yield point, Lüders' lines are shown by the resin at those points which have yielded. Thus, not only is the ratio of applied load to yield point obtained—and hence the relationship between stress and load in the elastic range, but the most highly stressed parts are immediately indicated on even the most complicated structure, and the Lüders' line pattern gives information as to the type and direction of stress.