. Transactions. herefore, apparently not suited,as it was hoped that it would be, for the determination of the mechanicalhistory of a steel or iron specimen, so long as the stresses in such specimenshave been at all times within the elastic limit. If the elastic limit has HANEMANN AND MERICA 213 been exceeded, and in particular if the yield point has been exceeded, thepossibility is given of subsequently determining this fact by the aid ofmagnetic measurements, such as have been here described. It was suspected that, since iron after having been stressed beyondthe yield point is in a metastabl
. Transactions. herefore, apparently not suited,as it was hoped that it would be, for the determination of the mechanicalhistory of a steel or iron specimen, so long as the stresses in such specimenshave been at all times within the elastic limit. If the elastic limit has HANEMANN AND MERICA 213 been exceeded, and in particular if the yield point has been exceeded, thepossibility is given of subsequently determining this fact by the aid ofmagnetic measurements, such as have been here described. It was suspected that, since iron after having been stressed beyondthe yield point is in a metastable state, indication of this fact would begiven by measurements of the magnetic permeability. Specimens weretherefore so stressed, the stress removed, and the permeability, or in-duction, measured for certain values of the field strength, after variousintervals of time. One bar showed, for certain medium values of thefield strength, a decrease of induction of from 40 to 70 gausses after 21 6,000 5,000 4,000 3,000. 2,000 r—V;;f 1,000 0 10 20 Fia. 12.—Material 3—Nickel, Abscissas—Stresses in Kilograms per SquareMillimeter. Ordinates—Inductions in Gausses. hr.; and the same total change after 24 days. The magnetic changein an overstrained iron specimen takes place, therefore, in that intervalof time in which the iron becomes again elastic, , in the period ofelastic recovery. In Figs. 9 and 10 are shown curves illustrating the effect of stress uponthe inductions B in the material 1, as delivered (hot rolled), and as an-nealed and quenched in water, respectively. It can be seen that, in thecase of the material as delivered, there is great irregularity in the induc-tion curves. Often the maxima occur at higher values of the stress forhigh than for low values of i^. In both cases, the material is in a stateof internal stress due to the manufacture and heat treatment, and it is 214 MAGNETIC STUDIES OF MECHANICAL DEFORMATION to the presence of these stresses that the irregu
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
