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Theta Projection Creep Life Model| Using Abaqus User-Subroutines for Creep Modelling of Gas Turbine Blades

Creep is one of the most significant failure modes in gas turbine components where the working temperature and stresses are high for a prolonged period of time. Existing creep models in commercial analysis software like Abaqus are not adequate to model all stages of creep namely – primary, secondary, and tertiary stages. Theta projection method is a convenient method proven to predict all stages of creep, especially the tertiary stage where strain rates are high leading to internal damage and fracture. The aim of the project is to develop a user subroutine for Abaqus to model creep in gas turbine components using the Theta projection method. The constitutive model for the Theta projection method based on the accumulation of internal state variables such as hardening, recovery, and damage developed by (R.W.Evans, 1984) is adopted to compile a Fortran code for the user subroutine. The user subroutine is validated through several test cases and comparing the results with experimental creep data. Creep analysis of a sample gas turbine blade is then performed in Abaqus through the user subroutine and the results are interpreted. Results of test cases validate the accuracy of the Theta Projection Method in predicting all primary, secondary, and tertiary stages of creep than existing creep models in Abaqus. Results at interpolated & extrapolated stress & temperature conditions with robust weighted least square regression material constants show the convenience in creep modeling with less input data than existing models. Results of creep analysis in a sample gas turbine blade not only predicted the creep life but also indicated the internal damage accumulation. Thus, creep modeling of gas turbine components through the user subroutine at different load conditions could lead us to more reliable creep life predictions and also indicate the regions of high creep strain for improvements in the early stages of design.

Simulation of pitting corrosion with scripting in Abaqus

Pitting corrosion is a form of extremely localized corrosion that leads to the random creation of small holes in metal. It can occur with random sizes and distributions, typically modeled as conical or cylindrical shapes. This type of corrosion reduces the strength of structures and increases stress concentration. So, it can lead to various destructive effects such as pipes bursting and reduced resistance to internal pressure. By pitting corrosion simulation, you can assess how corrosion affects stress, vibration, heat transfer, and other factors. This is crucial for enhancing the durability and safety of structures such as storage tanks, shafts, tubes, pipes, and other industrial components. This tutorial includes two scripts for pitting corrosion analysis. They help you to conduct Abaqus pitting corrosion simulation for different examples including a simple plate and a shaft.