1.1 This test method covers procedures for carrying out indentation plastometry, an indentation-based test technique to determine the plastic stress-strain properties of metallic materials, including yield strength, tensile strength and uniform elongation at necking, using inverse finite element analysis.

1.2 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 The indentation plastometry test can provide stress-strain curves that are comparable with those obtained from conventional tension testing.

5.2 Evaluation of the mechanical properties such as yield strength, tensile strength, and uniform elongation at necking is important throughout the lifecycle of metallic components. This includes during product development, in production for quality assurance and quality control, during service to inform repair strategies, planning preventative maintenance, and assessing residual lifetime, and after a component’s service life, to determine the root cause of a component failure. Established test method standards exist for measuring these mechanical properties, but these methods require large volumes of test material and the test specimen to be machined into a specific geometry, and result in the destruction of the component and test specimen.

5.3 The requirement to determine mechanical properties from a localized region, without the need to extract a test specimen, led to the development of indentation plastometry (1, 2)⁴. As an indentation-based test method, it can be used as a high-throughput test method to screen mechanical properties of metallic materials, and the mechanical properties can be mapped across a component (3). In addition, the test can allow for components that are in service to be tested in situ.

5.4 The indentation plastometry test method has some similarities with hardness testing (for which standards exist, for example Brinell or Vickers hardness), as it involves pushing a hard indenter into the surface of a material and measuring characteristics of the permanent indentation left after removal of the force. However, this method, by measuring the residual indentation geometry, not just the diameter, and combining it with inverse finite element analysis, allows for the extraction of yield strength and tensile strength values comparable with those obtained from conventional tension testing.

5.5 Fundamental Assumptions:

• 5.5.1 Tension-compression symmetry— The indentation plastometry test method utilizes a finite element model with the von Mises yield criterion to describe the plastic behavior of the specimen. This criterion assumes that the true stress-strain curve is the same in tension and compression. This assumption is appropriate for most metals, with some exceptions. Some exceptions include: metals with strong crystallographic texture and hexagonal close packed (HCP) crystal structure (4), cast irons, some nanocrystalline materials, and nickel-based superalloys that are directionally solidified or have strong crystallographic texture. Therefore, indentation plastometry can generally be used to determine properties comparable to those in a tension test.
• 5.5.2 Fracture— The indentation plastometry test does not probe the fracture properties of metallic materials and therefore cannot be used to determine the elongation at fracture. For brittle materials which fracture in a tension test before reaching the uniform elongation at necking, the indentation plastometry test will overestimate the tensile strength.
• 5.5.3 Plasticity law— Selection of an appropriate plasticity law for the material being tested is fundamental to the performance of the indentation plastometry test. The recommended constitutive plasticity laws (described in 7.5) limit the applicability to materials that have monotonic hardening behavior (Note 7).
• 5.5.4 Anisotropy— The indentation plastometry test method is not appropriate for materials with high anisotropy in the plane of the material being tested. 9.3.3.3 describes how to classify the amount of anisotropy to determine if the method is not appropriate for the plane being tested.