Abstract

Prediction of crack growth under creep condition is prime requirement in order to avoid costly and time-consuming creep crack growth tests. To predict, in a reliable way, the growth of a major crack in a structural components operating at high temperatures, requires a fracture mechanics based approach. In this Study a novel technique, which uses Finite Element Method (FEM) together with Artificial Neural Networks (ANN) has been developed to predict the fracture mechanics parameter (C*) in a 1%Cr1%MoV low alloy rotor steel under wide range of loading and temperatures. After confirming the validity of the FEM model with experimental data, a collection of numerical and experimental data has been used for training the various neural networks models. Three networks have been used to simulate the process, the perceptron multilayer network with tangent transfer function that uses 9 neurons in the hidden layer, gives the best results. Finally, for validation three case studies at 538°C, 550°C and 594°C temperatures are employed. The proposed model has proved that a combinations of ANN and FEM simulation performs well in estimation of C* and it is a powerful designing tool for creep crack growth characterization.

Highlights

  • Creep crack growth parameter (C*): Under constant load at high temperatures metals exhibit creep deformation

  • At elevated temperatures a body containing a defect may fail by creep rupture, fast fracture, creep crack growth or a combination of these processes

  • When subjected to stress at elevated temperatures creep crack growth may take place by the linking of voids and micro cracks that are generated on grain boundaries ahead of the crack tip

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Summary

Introduction

Creep crack growth parameter (C*): Under constant load at high temperatures metals exhibit creep deformation. Under steady state conditions (secondary creep rate) the stress and creep strain rate, may follow Norton’s creep law; ߝ௦ሶ௖ = ‫ܣ‬௦ߪ௡ೞ , where A and n are material constants (which may depend on temperature). At elevated temperatures a body containing a defect may fail by creep rupture, fast fracture, creep crack growth or a combination of these processes. When subjected to stress at elevated temperatures creep crack growth may take place by the linking of voids and micro cracks that are generated on grain boundaries ahead of the crack tip. Failure by creep crack growth is generally found to be inter-granular processes (Webster and Ainsworth, 1994)

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