Tensile Specimens to DIN 50125: Testing of Metallic Materials

If in practice it is necessary to deviate from the listed and very common specimen dimensions, the DIN 50125 standard accurately describes the fundamental requirements for these non-listed specimen geometries. This then also provides workshop-compliant dimensioning rules, which in turn allow the production of DIN EN ISO 6892-1 compliant tensile specimens.

The need to deviate from the listed and very common specimen dimensions can result from having to consider special material properties or the test arrangement and therefore the manufacturer’s specifications for testing machines and specimen grips.

An example are threaded-end specimens made of higher-strength materials. Although the specimen grip inserts are hardened or have a hard coating, the pressure applied to the surfaces that are in contact during the load application in the tensile test can become so strong that it causes damage or increased wear. Damages can occur to both the specimen grip side as well as the tensile specimen side. In such cases it is necessary to adapt the dimensions of the threaded ends accordingly, also in order to ensure correct and stable alignment of the tensile specimen throughout the entire test, thereby making sure that the test results are reliable.

In the case of flat products, an attempt is normally made to maintain the product thickness, that is to avoid processing of the original surfaces. DIN 50125 provides the user and manufacturer of the specimens with a simple diagram that illustrates the relationship between thickness a₀, width b₀ and initial gauge length L₀ of flat specimens with proportionality factor k=5.65 (short proportional specimen). With two specified sizes, the third one can then be read from this diagram. In a tensile test, the initial gauge length L₀ and the longitudinal strain are measured with an extensometer (optical or contact).

Since in the course of digitalization and tracking of specimens and their test results, specimen markings are required, DIN 50125 also provides simple, but important instructions for this: Markings must not influence the test results, must ensure clear legibility even after the test, and must be able to identify the specimen parts without any doubt even after specimen break.

The DIN 50125 standard provides dimensions and examples for tensile specimen measurements in nine different tables. The tables are paired—where necessary—with specimen technical drawings to provide the manufacturing workshop with all required information for specimen preparation when using the DIN 50125 standard.