97 International Journal of Mechanical and Materials Engineering (IJMME), Vol. 3 (2008), No.1, 97-104. FATIGUE LIFE AND CRACK PATH PREDICTION IN 2D STRUCTURAL COMPONENTS USING AN ADAPTIVE FINITE ELEMENT STRATEGY Abdulnaser M. Alshoaibi and A. K. Ariffin Department of Mechanical & Materials Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan, Malaysia E-mail: alshoaibi@gmail.com ABSTRACT Fatigue crack propagation in two-dimensional structural components under constant amplitude loading is analyzed using an adaptive finite element procedure. The stress- intensity factors are estimated by using displacement correlation technique utilizing the purposely constructed singular elements around the crack tip with automatic remeshing algorithms. The propagation is modeled by the successive linear extensions under the linear elastic assumption. Subsequently, the fatigue life cycle is estimated based upon Paris’ equation. The test for the first specimen which is the single centered angled crack is applied only to show the accuracy and efficiency of this method to calculate accurate values of stress intensity factors. Subsequently, fatigue analysis is applied for two geometry specimens namely, single edge angled crack and modified four points bending SEN specimen. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that the program is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily Key words: Fatigue; adaptive mesh; finite elements; crack propagation; stress intensity factors; constant amplitude loading. 1. INTRODUCTION There are many different mechanical failure exists in simple or complex modes. The deterioration of engineering structures due to fatigue has been a difficult problem facing engineers for many decades. It has been estimated that between 50 and 90 % of these failures are due to fatigue (Solanki 2002). Fatigue life prediction of the structural components is therefore has become one of prime considerations in many fields of engineering. The prediction by the method involving the estimation of the crack path, the associated stress intensity factors, and the crack propagation rates at each step is a challenging problem (Harter 1999, Ustilovsky 1999 and Pantelakis 1987). Practically, numerical techniques such as finite element method, boundary element method and meshless method are sought to solve this problem. Fatigue life prediction is still very much an empirical art rather than a science (Pugnoa et al. 2006), despite being a relatively old subject having nearly 150 years of history (Wöhler 1860), described in a number of books or review papers. The major source of failure of structural components is fatigue crack growth. In the past, the S–N curves were the only engineering tools, and crack propagation was not considered to predict lifetime. Nevertheless, at present, studying crack growth behaviour has been made possible by the LEFM and the prediction of remaining lifetime of components is accessible (Courtin et al. 2005). This is of great practical importance in order to know if a part can be still used or must be replaced. One of the main objectives in fatigue design is the prediction of crack growth rate with respect to the number of cycles of a cyclic solicitation. Traditional, empiric models (Paris, Walker, Forman and Priddle) are used for fatigue crack growth prediction. These models need the stress intensity factor history along the crack pat, which is only available for typical and simple component geometry and loading (Tada et al. 2000). Miranda et al. (2003) developed two complementary software to predict the fatigue life and crack path in 2D structural components under constant amplitude loading. The first one, named Quebra2D, which is an interactive graphical program for simulating 2D fracture processes based on a finite element self adaptive mesh generation strategy. The results of this software are export to the second program, named ViDa, which is general purpose fatigue design software to predict the fatigue life. An adaptive mesh finite element program has been developed recently for simulating 2D linear elastic crack propagation (Alshoaibi et al. 2007). This program is written in FORTRAN. In this work, it is further extended to analyze the fatigue crack growth under constant amplitude loading. The finite element program is developed in such that the fatigue life is directly predicted after the associated stress intensity factory history along the crack path is completely recorded. 2. MESH GENERATION AND ADAPTIVE REFINEMENT In this work, the unstructured triangle mesh is automatically generated by employing the advancing front method