Standard for testing tensile strength of metallic materials is revised

ISO 6892-1 enables designers and engineers of metallic products and components, specifiers, and the insurance industry to define the mechanical properties of metallic materials at room temperature.

In 2009, ISO 6892-1 introduced Method A, the method of test control based on maintaining a strain rate. The more traditional method, now referenced as Method B, is based on maintaining a stress rate during elastic region of a tensile test. However there has been confusion around Method A and how the strain rate is measured whether it can be done using a closed loop method or a crosshead separation. As such ISO 6892-1:2016 includes additional separation of methods, introducing Method A1 (Closed-Loop Strain Control) and Method A2 (Constant Crosshead Separation Rate).

ISO 6892-1 can test metallic sheets and plates, wire, bar or section, rebar, and tubes. Specimens are gripped securely ensuring axial alignment for minimal bending and the specimen is strained in tension until failure using either Method A or Method B control modes. During this time, the load, crosshead extension, time, and strain data are recorded to determine the material characteristics.

As Method A is the recommended method of control, the goal is that this further clarification will assist with test labs that are transitioning from Method B towards Method A and monitoring the specimen strain rate.

Dan Palmer, head of market development for manufacturing at BSI, said: “Materials testing is critically important in structural engineering where the calculations must be accurate for building solid and safe constructions. The aerospace industry also demands rigorous measurement for metallic components used in aeronautical engineering. As a result, having a standard in place that adds confidence to the process is essential.”

Benefits of ISO 6892-1:2016 include:

• Method A can help minimise the variation of the test rates during the moment when strain-rate sensitive parameters are determined and minimize the measurement uncertainty of the test results
• Allows more repeatable and comparable results to be produced
• When using Method A1, there can be considerable time savings
• Makes recommendations for computer controlled testing machines
   

The international standard can also be a useful reference for major fabrication contracts between manufacturers and customers.

ISO 6892-1 was developed using a consensus-based collaborative approach with input from experts from the materials, special metals testing and quality management industries. Organizations including the British Civil Engineering Manufacturers Association, GAMBICA Association, National Physical Laboratory (NPL), UKAS (United Kingdom Accreditation Service) and University of Warwick contributed to the process.