A New Computational Framework for Fatigue Crack Growth Analysis of Components

摘要

Two contrasting methods are traditionally available to analyze fatigue crack growth (FCG) lifetime in components. On the one hand, engineering software such as NASGRO and AFGROW provides pre-programmed stress intensity factor (SIF) solutions for simplified crack and component geometries, sophisticated crack growth equations including load interaction models, and relatively fast execution times-often only a few seconds. However, the SIF solutions in these codes are often for simple uniform or linear stress distributions, and the user is left with the task of interpreting how best to transfer dimensions and stresses manually from component models into the simplified fracture models. On the other hand, numerical fracture software such as FRANC or BEASY offers integrated modeling of the crack in the component, calculating the SIF more accurately with finite element (FE) or boundary element (BE) methods based on the actual three-dimensional (3D) crack and component geometries and stresses, and updating the mesh as the crack grows. However, these codes generally offer a limited menu of crack growth models for complex variable amplitude loading, and their execution times for large load spectra can be extremely long in some cases-perhaps several hours. Neither of these classes of FCG analysis methods is typically integrated directly with reliability assessment to determine the probability of fracture. Some external linkage with an independent computer program is usually required to perform this calculation, and this introduces further inefficiencies into the analysis process. In this paper, a new framework for FCG analysis of components is described that offers a unique balance of accuracy and efficiency, fully integrated with reliability assessment. New weight function (WF) SIF solutions with high accuracy and efficiency accommodate complex stress gradients throughout the crack plane. A sophisticated graphical user interface (GUI) provides a direct interface with 2D or 3D FE models to extract and visualize geometry and stress information. The GUI can also build an optimum fracture mechanics model automatically with little user intervention. Advanced FCG algorithms are integrated directly with probabilistic algorithms to calculate reliability. Ultimately, this framework will facilitate automated reliability calculations addressing all potential crack locations in the component.