The precision of the results of tensile tests is limited by factors related to material, test piece, testing equipment, test procedure and method of calculation of the mechanical properties.
More specifically, the following causes of uncertainty can be mentioned:
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— some degree of inhomogeneity, which exists even within a processing batch obtained from a single heat of material;
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test piece geometry, preparation method and tolerances;
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— gripping method and axiality of force application;
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testing machine and associated measuring systems (stiffness, drive, control, method of operation);
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measurements of test piece dimensions, gauge length marking, extensometer initial gauge length, measurement of force and extension;
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test temperature and loading rates in the successive stages of the test;
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human or software errors associated with the determination of the tensile properties.
The requirements and tolerances of this International Standard do not permit quantification of the effect of all these factors. Interlaboratory tests can be used for an overall determination of the uncertainty of the results under conditions close to the industrial practice of the test. They do not, however, permit separation of effects related to the material from errors due to the test method.