Abstract
Instrumented indentation tests are an efficient approach for the characterization of stress–strain curves instead of tensile or compression tests and have recently been applied for the evaluation of mechanical properties at elevated temperatures. In high-temperature tests, the rate dependence of the applied load appears to be dominant. In this study, the strain-rate-dependent plasticity in instrumented indentation tests at high temperatures was characterized through the assimilation of experiments with a simulation model. Accordingly, a simple constitutive model of strain-rate-dependent plasticity was defined, and the material constants were determined to minimize the difference between the experimental results and the corresponding simulations at a constant high temperature. Finite element simulations using a few estimated mechanical properties were compared with the corresponding experiments in compression tests at the same temperature for the validation of the estimated material responses. The constitutive model and determined material constants can reproduce the strain-rate-dependent material behavior under various loading speeds in instrumented indentation tests; however, the load level of computational simulations is lower than those of the experiments in the compression tests. These results indicate that the local mechanical responses evaluated in the instrumented indentation tests were not consistent with the bulk responses in the compression tests at high temperature. Consequently, the bulk properties were not able to be characterized using instrumented indentation tests at high temperature because of the scale effect.
Highlights
A database of fundamental material properties is essential for effective utilization of existing materials and exploration of new materials
Because a unique stress–strain relationship cannot be estimated from the P − h curve of a single indentation test using a standard sharp indenter [21,22,23], dualindenter and sphere indenter methods were proposed to determine a unique set of material constants in a simple constitutive model
We developed an approach for estimation of strain-rate-dependent plasticity based on the results of the high-temperature indentation tests
Summary
A database of fundamental material properties is essential for effective utilization of existing materials and exploration of new materials. Instrumented indentation tests are an efficient approach for the evaluation of mechanical properties, such as effective elastic stiffness and hardness These tests require less effort for specimen preparation and provide multiple results from a single specimen. Instrumented indentation tests at elevated temperatures have attracted considerable attention for the characterization of the temperature dependency of mechanical properties, which has the potential for efficiently obtaining material databases for the research and development of heat-resistant materials. Because a unique stress–strain relationship cannot be estimated from the P − h curve of a single indentation test using a standard sharp indenter [21,22,23], dualindenter and sphere indenter methods were proposed to determine a unique set of material constants in a simple constitutive model. We developed an approach for estimation of strain-rate-dependent plasticity based on the results of the high-temperature indentation tests. The estimated mechanical properties were validated using a compression test at the same temperature
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