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Method of test at room temperature. This document Older versions. Click here to find out how to access this document. This also means that the standard requirements address important influencing factors and generally formulate requirements in such a way that there is enough leeway for technical realizations and innovation.
Important characteristics of tensile testing on metals to ISO include:. The maximum tensile force after exceeding the yield point can also lie below the yield point for weakly work-hardened materials, therefore the tensile strength in this case is lower than the value for the upper yield point.
The stress-strain curve image shows a curve with a high level of work-hardening 1 and with a very low level of work-hardening 2 after the yield point. For metals with yield point and subsequent stress, on the other hand, the tensile strength corresponds to the stress at the yield point.
The most important and clearly describable requirements also relate to force measurement and the measurement of extension of the specimen under force application. The calibration processes, and especially the results and definitions of the classifications, are described in the standards for force measurement and extension measurement. The latter is crucial for application in the testing practice. Maximum permitted deviations and resolutions can be derived through the class affiliation for the calibrated measuring system, which have to be used for the determination of the measurement uncertainty of the measuring system.
One exception to be noted is the evaluation, and with that the classification of the extensometers. An extensometer that is intended for small initial gauge lengths must meet higher measuring requirements than one for bigger initial gauge lengths. Characteristic values, for which use of an extensometer of at least Class 1 to ISO for tensile testing of metal is required, are:. Characteristic values, for which use of an extensometer of at least Class 2 to ISO for tensile testing of metal is required, are:.
For correct determination of yield points R eH and R eL and offset yields Rp and Rt , besides accurate force and strain measurement, the test speeds are also significant:. Since both ISO and ASTM have equally adapted the so called strain rate control in their standard for tensile testing on metals, in order to improve the results reliability in the determination of yield points and offset yields. The first method uses the modern technical options provided by drive controllers to automatically maintain the crosshead speed in the tolerance range for the strain rates specified by the standard.
This method requires a control-technology-equipped testing system, however it significantly simplifies the test operation and eliminates errors in setting the crosshead speed.
Therefore this control method is recommended. The strain at break A or At is a measurement of the ductility, as well as the flow properties of a material. The strain at break At can only be determined with extensometers , which remain on the specimen up to and including the point of break, and measure the extension of the specimen. Strain at break A was normally measured manually, while today it is also measured with extensometers.
For automatic measurements, correct determination of the point at which the specimen breaks point of break is therefore of significant importance. Modern algorithms, which automatically analyze the stress-strain curve, ensure reliable specification of the break point and accurate determination of the strain at break.
The break location along the specimen, more specifically along the parallel length of the specimen, is also important for reliable and accurate determination of the strain at break.
If the break or point of failure is not within the gauge length of contact-type extensometers, the plastic deformation that occurs during necking and the point of failure cannot be correctly determined.
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