How to determine the yield stress

The limit of fluidity is the magnitude of the mechanical load (stress) at which the material irreversible deformation, changes its size and shape. The amount of yield today is used for determining the qualitative characteristics of metals, steels. It affects the strength of metal structures, fasteners, and mechanisms.

Instruction

1. For hard steels which do not have a site of fluidity, define the conditional limit of fluidity, which is determined when reaching 0.2% of residual deformation. There are special tables that the values for the limits of yield strength for different materials and steels. Values are defined by the relevant Standards adopted in Russia.
2. To determine the limit of yield stress using two methods: analytical and graphical.An analytical method. In accordance with the recommendations of GOST, select the rebar sample (material) for testing and determine its initial cross-section by measuring or determining the appropriate formula. Place the sample in the tensometer, corresponding to GOST 18957-73, spend a couple of tests, measuring the magnitude of mechanical stresses and cross-sectional area, the magnitude of the elongation up to rupture of the material. Determine the limit of fluidity of the sample by the formula, where it is equal to the ratio of the applied (measured) mechanical stress to the initial cross-sectional area of the sample. Measured in MPa (kgf/mm2).
3. The graphical method is plotting the "tension-elongation" of the sample in the tensometer. Take graph paper and construct a coordinate system in which the axis of ordinate (y) defer the load applied to the material during the test, and the horizontal axis (x), and the amount of deformation (elongation) of the sample until its break. The force corresponding the limit of yield strength of the sample is determined at the point of intersection of a straight line corresponding to the load acting on the sample at the time of testing, with the tension diagram.
4. The definition of conditional limit of fluidity is allowed in accordance with GOST 1497-84, engine diagram, subject to periodic check tests of samples using strain gauge, what should be recorded in the normative-technical documentation for manufactured products.
5. The physical quantity is the limit of fluidity is now used for international use under the name of most grades, since most fully determines its structural characteristics.