Development of a triaxial-test to measure properties of ceramic powder

The manufacture of superconducting tapes based on the ceramic high temperature superconductor (HTS) is a promising product for high current applications such as electro-magnets and current transmission cables. The tapes are manufactured by using the “Powder in Tube” method (PIT). This implies drawing and rolling of metal tubes containing powder. The mechanical processing of the tape is critical to the final result; as such it becames imperative to understand the mechanical properties of the superconducting powder used. The aim of the present work is to perform and opimize an alternative tri-axial test, called the Powder in Flexible die test (PFD), for powder testing in order to characterize the plastic properties of MgB2 powder and to define the yield surface for a fixed relative density of 77%. The attention has been focused on the test and refinement of PFD-test in order to define its reproducibility and to fit a yield surface for a fix density and to the Drucker-Prager model. The characterization of the plastic properties of MgB2 powder will be useful for the definition of plastic behaviour of the powder during the flat rolling, a key step of Powder In the Tube process (PIT). The results collected in the lab show a good degree of reproducibility of PFD-test. The low scattering of the data, obtained during PFD-test, with the results of three additional tests: Diametrical Compression test, Uniaxial Compression test, Die Compaction test, has resulted in obtaining of a yield surface for MgB2 with 77% of relative density. Finally the yield surface has been fitted to the Drucker-Prager model.