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Methods are given for resolving measured bending strains into contributions from the following three sources: first, inaccuracies in the gages or their application; second, nonsymmetry of the specimen; and third, imperfections in the apparatus. The methods are applied to tests on tension specimens with three commonly used forms of grip ends. A method for correcting for inaccuracies in gage factors and gage misalignment is derived and applied. After correction by this method gage errors are insignificant. For the accurately machined, ½-in.-diameter specimen used, the specimen contribution to bending is small. The calculated apparatus contribution is most reproducible and significant when the load string has a minimum number of loose, threaded joints. The three specimens tested give bending strains well within the limit of ASTM recommended practices when the testing machine is in good condition.
A method also is explained for determining the maximum bending strain at any point in the reduced portion of the specimen. By this method it is shown that the maximum may be more than twice the value measured by using an extensometer or strain gages centered on the reduced portion.
bending, strains, tension tests, bend tests, elastic properties, loads (forces), measurement, strain gages, calibration
Manager, Physical Testing, Mechanical Engineering, Materials and Processes Laboratory, Large Steam Turbine-Generator Div., General Electric Co., Schenectady, N. Y.