On the use of small ring testing for the characterisation of elastic and yield material property variation in additively manufactured materials

Abstract

• Material properties are shown to vary over an additive manufacture build volume. • Small ring samples are used here to investigate a Ti-6Al-4V alloy. • Analytical and numeric methodologies are developed for tensile data interpretation. The present work introduces a small volume, high throughput testing method that may be used to quickly, and with high spatial fidelity, investigate local material properties in additively manufactured materials. A case study application is presented here, considering components made from the alloy Ti-6Al-4V by the powder bed fusion process. Novel tensile small ring samples are produced at multiple locations over the print volume and are tested in order to estimate local tensile material responses. An inverse method is implemented in order to estimate representative material properties at each testing location by optimising initial values against sequential finite element model results. Initial estimates themselves are found through a geometrically non-linear semi-analytical model that approximates elastic material response. A good level of repeatability is noted between small ring tests conducted at specific build locations, suggesting a limited effect of build height on constitutive response and robust testing/analysis methodology. Small ring tests indicate a mean Young's modulus of 82.83 GPa (with a standard deviation of 4.57 GPa) and a mean yield stress of 655.58 MPa (with a standard deviation of 115.73 MPa). Full sized “conventional” tests, published in the author's previous work, indicate a Young's modulus of 114.45 GPa and a yield stress of 771.266 MPa. Limited fractography has indicated that there is a wide variation in porosity across the build volume, suggesting that the deviations in local material properties are due to the use of a reduced print volume in specimen manufacture.