Next Generation Materials Testing: Obtaining Anisotropic Plasticity Parameters using Profilometry-based Indentation Plastometry (PIP)

Mechanical testing is routinely used in almost all industrial sectors. It is used to ensure the quality and safety of components (often mandated by regulations), to reveal important relationships between processing and properties, and to support the development of new materials and novel material systems.

The gold-standard for mechanical testing is the tensile test, which measures the stress-strain properties of materials. This test involves machining of a large test coupon and requires access to a universal mechanical test machine. Although widely used, the tensile test can be time-consuming and cumbersome, with testing turnaround times of hours or even several days if outsourced, and the machinery and capital set-up costs are high. In addition, the tests result in the destruction of the sample and they generate large amounts of wasted material. Despite the clear need for improved testing methods, a risk averse sector and an over-reliance on compliance with the testing standards has hampered progress within this area. It is now evident that current testing procedures are out-dated and inflexible. There is a strong motivation for developing faster, more efficient, more cost-effective, and less wasteful testing methods.

The Plastometrex (PLX) team have developed an innovative mechanical testing method for metallic materials called PIP (or Profilometry-based Indentation Plastometry). PIP measures the same stress-strain properties as the tensile test while overcoming many of its limitations. It is simple to use, reduces testing turnaround times from hours to just three minutes, sample preparation requirements are minimal, and real components can be tested. It is similar in execution to the common hardness test, but unlike the hardness test the entire residual profile shape is measured. The PIP methodology involves three main tasks: (1) Creation of an indent using our Indentation Plastometer (see www.plastometrex.com), (2) Measurement of the residual profile shape using an integrated stylus profilometer, and (3) Analysis of the residual profile shape using our proprietary software package - SEMPID.

PIP is well-suited for materials that are isotropic, i.e. its properties are the same in all directions. However some materials, such as additively manufactured (AM) metals, are anisotropic, i.e. their properties vary depending on the orientation. This research project will extend the capabilities of PIP to include anisotropic materials with a focus on AM metals, allowing quantitative assessment of the properties in different directions. AM could revolutionise the high value manufacturing sector, allowing rapid prototyping, radical design innovation, lower tooling costs, reduced time to market and lower production costs, waste and emissions. This research will allow these components to be rapidly tested, and provide manufacturers with almost real-time feedback on the properties of their parts. Therefore, it is an enabler for AM technology and the potential benefits for manufacturing and wider society that this brings.

The research will mainly take place at Plastometrex Ltd, the host organisation of the fellow, based at the Cambridge Science Park. The research will involve a significant amount of laboratory experiments and modelling work. Oxford University are partners on the project, with their interest in high-throughput testing of AM superalloys, a family of materials that are ubiquitous in aero-engine and power-generation industries. The Manufacturing Technology Centre (MTC) are collaborators on the project. They will provide materials for the research, equipment for characterising the amount of structure of porosity, and their leading knowledge of materials, processing and post-processing for AM metals. The National Physical Laboratory (NPL) will collaborate on the development of a standard for the methodology and conduct tensile test experiments for blind testing as part of technology validation.