ISO 6892-1:2016 Tensile Testing Metallic Materials
This European standard was introduced in July 2016, superseding the 2009 version which replaced the withdrawn EN 10002-1:2001 standard. It specifies the method for tensile testing of metallic materials and defines the mechanical properties that can be determined at ambient temperature. Instron® participates on the committee, ensuring our products are compliant and our team is educated about the changes and the effect they will have.
Products that may be tested in accordance with this standard include metallic sheets and plates, wire, bar or section, rebar, and tubes. Specimens need to be gripped securely ensuring axial alignment in order to minimize bending. The specimen is then strained in tension until failure using either Method A1/A2 or Method B control modes. During this time, the load, crosshead extension, time, and strain data are recorded to determine the material characteristics. The typical calculations include: Yield Point (Rp, Reh, Rel), Ultimate Tensile Stress (Rm), and specific strain values at calculations (A, Agt etc.). ISO 6892-1 also specifies the specimen geometries that should be used depending on the type of product that is being tested.
In 2009, ISO 6892-1 introduced Method A, the method of test control based on maintaining a strain rate. The more traditional method, now known as Method B, was based on maintaining a stress rate during the elastic region of tensile test. There could be confusion around the introduction of Method A. Many understood this as only being achievable using equipment capable of closed-loop strain control, but this is not true. It is possible to conform to Method A using a constant crosshead separation rate.
To make this more clear, ISO 6892-1:2016 incorporated additional separation of methods, introducing Method A1 (Closed-Loop Strain Control) and Method A2 (Constant Crosshead Separation Rate).
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. The benefits remain the same: Method A is intended to minimize the variation of the test rates during the moment when strain-rate sensitive parameters are determined and to minimize the measurement uncertainty of the test results. Implementing Method A1 strain control, significantly improves testing throughput as well as a decreases result variability across machines and laboratories.The challenges of testing to this standard are:
- Conforming to stringent control modes
- Comparability of results
- Accurate strain measurement
- Automatic compliant calculations
- Secure gripping of varying specimens
- Conforming to Stringent Control Modes – Using advanced controller technology, it is possible to achieve up to a 40% decrease in test time using Method A Closed Loop Strain Control, ultimately improving throughput
- Comparability of Results – When testing to Method B where the strain rate on the specimen will vary system to system, using a stiff Instron frame will ensure accurate results for improved comparability across different sites
- Secure Gripping of Varying Specimens – Varying gripping techniques from DuraSync Side Acting Grips to manual wedge grips with optimized tooth pattern ensures no slippage occurs
- Automatic compliant calculations – Instron Bluehill® testing software has advance pre-built methods available with pre-configured metal-specific calculations helping to ensure compliance
- Accurate Strain Measurement – Advanced strain solutions for contacting and non-contacting stain measurement that can meet or exceed the accuracy requirements of ISO 6892-1
The imminent release of ISO 6892-1:2016 will provide further clarification on the significant changes that were introduced in ISO 6892-1:2009, including the testing rates based on strain rate (Method A). To better clarify the requirements of Method A, ISO 6892-1:2016 now includes two clearly defined approaches, Method A1 (Closed-Loop Strain Control) and Method A2 (Constant Crosshead Separation Rate).
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