Journal Published Online: 29 July 2020
Volume 9, Issue 1

On the Constraint Factor Relating Uniaxial and Indentation Yield Strength of Polycrystalline Materials Using Spherical Microindentation

CODEN: MPCACD

Abstract

High-throughput (HT) material property characterization has become increasingly important for the rapid and cost-effective development of new material systems. In recent years, spherical indentation using the Pathak-Kalidindi (P-K) protocol has been shown to be a reliable and HT method for capturing the elastic-plastic properties of several different types of materials. However, because of the higher hydrostatic pressure under the indenter tip and the constraint of the surrounding elastically deforming material, the indentation yield strength is higher than the uniaxial yield strength and they can be related by a scaling factor, referred to as the constraint factor. For fully plastic indentation, the constraint factor was found by Tabor to be ~2.8. However, the constraint factor is not well defined for elastic-plastic indentation and depends on the strain induced. In this work, the application of the P-K indentation protocol is demonstrated on a set of aluminum 7050 samples that have undergone different solution and aging treatments. Conventional uniaxial tensile and compression tests were also conducted on the same material. The constraint factor at the 0.2 % offset yield point was determined from the indentation and uniaxial measurements to be ~1.4. Experimental observations from our work and a similar work on aluminum 6061 showed a dependence of the constraint factor at the 0.2 % offset yield point on the uniaxial plastic properties. To explain these experimental observations, further investigation was carried out using finite element simulations of spherical indentation on materials with different yield strengths and hardening parameters. New insights are provided on the constraint factor at the 0.2 % yield point, which show that it increases with the ratio of the plastic to elastic strain. It was also found that the effect of the hardening is much less than that of the yield strength on the constraint factor at the 0.2 % yield point.

Author Information

Bhat, Anirudh
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
Neu, R. W.
George W. Woodruff School of Mechanical Engineering and School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, USA
Pages: 22
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Stock #: MPC20190260
ISSN: 2379-1365
DOI: 10.1520/MPC20190260