冷間引抜せる鋼管中の残留応力 (I)

Abstract

As a first step to study on residual stress in cold-drawn steel tubing, the author performed a preliminary test for determining the residual stress in tube-shaped test specimens. In selecting the various methods of measurement of residual stress, the author decided to adopt Sachs and Espey's splitting method, and investigated fully on this method, then obtained the following results.(1) For determination of the diameter change, Sachs and Espey used an optical comparater and measured the length between the gauge points plotted on the outer surface both sides of the split line before and after splitting. But if, by splitting, there should take place the elastic deformation at the outer surface of the opposite arc, then the diameter change measured by this method resulted in the inclusion of this error. Therefore except for tubings with small diameter or thin wall thickness, this method was inferior, in regard to accuracy, to that which had been calculated from the mean outside diameter measured with a micrometer.(2) But, when the author measured the diameter with a micrometer, if the wall thickness of the specimen tube be thin, the specimen was deflected by measuring pressure and this deflection resulted in an error in measurement. Then the author obtained the relationships between the specimen dimensions and the deflection amount by calculations. (Fig. 3)(3) As the result of the above fact, the author revealed that the measurement with a micrometer within the size ranges of ordinary steel tubing was superior, in accuracy, to that with an optical comparater and he decided to perform the measurements with a micrometer thereafter.(4) In order to determine the specimen length, the author measured the residual stress in the specimens of various lengths and revealed that the length should be 2 to 2·5 times the outside diameter. (Fig. 4)(5) The author further obtained by accurate method the distribution diagrams of residual circumferential stress (Fig. 8 & 9) in plug-drawn and sunk steel tubing which had been drawn with two dies of different contour. (As to contours of the die and plug, see Fig. 5 (a) & (b)). As compared with those obtained by approximation method, it was made known that a general tendency was to be revealed through measurement values obtained by approximation method as far as sunk steel tubing and those which plug-drawn with (b) type die were concerned.