Characterization of the Strain-Rate-Dependent Plasticity of Alloys Using Instrumented Indentation Tests
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Instrumented indentation tests are an efficient approach to characterize stress--strain curves instead of tensile or compression tests and have recently been applied to evaluate mechanical properties at elevated temperatures. In high-temperature tests, the rate dependency of the applied load appears 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 of the estimated material response. 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 cases of slow test speeds in compression tests. The results indicated that the error comes from the material behavior of polycrystalline aggregate such as grain boundary sliding in the compression tests because the deformation area of instrumented indentation tests is small enough to evaluate the material behavior of single crystal.
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