Viscoplastic behavior of notch roots at high-temperature

A number of so-called unified viscoplastic models are available to simulate the time-dependent behavior of metals. These constitutive models were developed with the finite-element structural analysis of hot section engine components as their primary objectives. The Bodner-Partom model is one of the most popular unified viscoplastic models so far in the United States, and it has been incorporated into finite element software for structural analysis in the aircraft industry within recent years.; This work presents the first experimental measurement of biaxial principal elastoplastic strains at a U-notch at a high temperature of 650{dollar}spcirc{dollar}C for viscoplastic behavior investigation of the hot section engine material Inconel 718. The biaxial strain measurements permit experimental determination of the complete stress-strain state at the notch root.; This experimental data is used to evaluate the three-dimensional Bodner-Partom model incorporated into the finite element software ABAQUS. The evaluation requires two sets of experiments at high temperature. The first set contains constitutive tests on smooth specimens for determination of the material constants in the model. For the second set, a laser-based optical technique is extended to measure biaxial elastoplastic strains at the notch root. The oxidation problem on the specimen surface was solved by employing a thin film silicon coating technique and using an argon atmosphere. These experiments include monotonic tensile tests with maximum strain value of approximately 1 percent, cyclic tests up to three cycles, and creep tests of about ten hours.; The experimental work is presented in the thesis, including both the constitutive tests and the notched specimen tests. Comparison of the test results with model predictions shows that the three-dimensional model can simulate the viscoplastic behavior of metals in complicated structures at elevated temperature.