Metallurgy; an introduction to the study of physical metallurgy . vantages hitherto attachingto autographic apparatus forthis purpose, and makes itpossible to obtain extremelyaccurate and detailed dia-grams with very little trouble,and even on tests carried outat exceptionally rapid have already referred toit as a means of measuringthe stresses applied to a test-bar without the use of a leveror hydraulic measuring cham-ber, but the manner in whichthe autographic stress-strain diagrams are obtained is worthyof brief mention. As already indicated, in the Dalby apparatus the stress istra
Metallurgy; an introduction to the study of physical metallurgy . vantages hitherto attachingto autographic apparatus forthis purpose, and makes itpossible to obtain extremelyaccurate and detailed dia-grams with very little trouble,and even on tests carried outat exceptionally rapid have already referred toit as a means of measuringthe stresses applied to a test-bar without the use of a leveror hydraulic measuring cham-ber, but the manner in whichthe autographic stress-strain diagrams are obtained is worthyof brief mention. As already indicated, in the Dalby apparatus the stress istransmitted to the test-bar through a weigh-bar, whoseelastic extension measures the amount of the stress. Thisweigh-bar takes the form of a cylindrical rod of nickel steelwhose core has been bored out so as to form a thick-walledtube. This tube is shown as WW in the diagram of theapparatus given in Fig. 86. To the lower end of the weigh-bar,W, is attached the test-piece, P. Liside the tube, W, is placeda vertical distance-piece, t. If now W is stretched through a. L- Loner ?? \ ^>3 ^•»c^« Pig. 86.—Diagram of theApparatus. Dalby THE MECHANICAL TESTING OF METALS 209 short distance, there will be a small relative moyement of theupper end of the piece, t, and of the small projections (1 and 2)connected to the upper end of W. A small mirror is mounted onthree points in such a way that the sUght relative movement of tand 1, 2 causes the small mirror to tilt, thus forming a sensitive optical lever, by means of which the minute extensions ofW are sufficiently magnified. A beam of light from the lamp Zis reflected down on to the mirror of this optical lever and upagain from it to another mirror, N, and thence to the ground-glass screen or the photographic plate at F. Now matters areso arranged that the movements of the httle mirror at theupper end of t serve to move the beam and the resulting spotof hght on the ground glass or the plate in a horizontal direction,thus providing th
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectmetals, bookyear1922
