Conference Paper

Fatigue Failure Predictions Based on FEA Fracture Mechanics Simulations

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Abstract

Fatigue is an important ageing mechanism for long-term operation (LTO) of nuclear power plants. The effect of the reactor coolant environment on fatigue is one of the factors to take into account. Application of environmental fatigue codes, generally, leads to large margins for actual fatigue failure of components. In combination with longer operation times, these margins can make it challenging to meet the criteria defined in the standards. The purpose of the work in this paper is, therefore, to gain insight into the conservatism in typical fatigue analyses using design fatigue curves which is done by analyzing the fatigue process up to the actual component failure using crack growth analyses. Prediction of fatigue failure in cylindrical specimen is investigated through numerical simulations of fracture mechanics. A finite element analysis model is implemented for a crack in a cylindrical specimen typically used for fatigue life testing and generating design fatigue curves. The specimen is uniaxially displacement-loaded into the plastic regime, and the reaction force is evaluated as a function of crack depth and shape. Cyclic loading leads to formation of a crack with the depth such that a failure point in the S-N curve corresponds to the 25% load drop. Stress intensity factors are calculated, and number of cycles to failure are determined based on Paris’ law and a two-stage crack growth relationship. Simulation results are compared to experimental fatigue life data and show good agreement. The outcome of the investigation can be extended to fatigue life of geometrically complex thermo-mechanical components, such as nozzles, under transient thermal loading occurring during operation of a nuclear power plant, in order to assess conservatism of fatigue failure criteria based on experimentally obtained S-N design curves.

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... HD Wlide [70] investigated the prediction of fatigue damage in cylindrical specimens by numerical simulation of fracture mechanics. A finite element analysis model was developed for cracks in a typical cylindrical specimen used for fatigue life testing and generation of design fatigue curves. ...
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In recent years, with the development of industry and scientific technology, the demand for materials has been increasing. Fatigue crack propagation is an important issue in the field of materials, and developing relevant theories and methods, understanding the mechanisms of fatigue cracks, and making scientific predictions on fatigue crack propagation are hot topics both domestically and internationally. Fracture mechanics, as a discipline studying the strength and propagation of cracks in materials, has developed a relatively complete theoretical system and engineering application methods over more than 100 years of continuous development. This article focuses on the effects of factors such as temperature, stress ratio, and load frequency on the fatigue crack propagation characteristics of metallic materials, and summarizes the common theories and methods of fatigue crack propagation.
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