Estimation Of Coefficients Of Williams' Series In Lefm Problems Using Decoupled Equations Method
The existence of crack and notch is a significant and critical subject in the analysis and design of solids and structures. As most of cracked domain problems do not have closed-form solutions, numerical methods are the current approaches dealing with fracture mechanics problems. This study presents a novel application of the decoupled equations method (DEM) to model crack issues. Based on linear elastic fracture mechanics (LEFM), the first four coefficients of the William's series for the crack tip's asymptotic elastic field are computed using the DEM. In this method, only the boundaries of problems are discretized using specific higher-order sub-parametric elements and higher-order Chebyshev mapping functions. Implementing the weighted residual method and using Clenshaw-Curtis quadrature result in diagonal Euler's differential equations. In the present method, the so-called local coordinate's origin (LCO) is selected at a point, from which the entire domain boundary may be observed. For the bounded domains, the LCO may be chosen on the boundary or inside the domain. Furthermore, only the boundaries which are visible from the LCO need to be discretized, while other remaining boundaries passing through the LCO are not required to be discretized. Consequently, when the local coordinates origin (LCO) is located at the crack tip, the geometry of crack problems is directly implemented without further processing. In fracture mechanics problems, the stress at the crack tip approaches to infinity, and hence the original DEM is not able to represent infinite stress at the crack tip, basically. To overcome this problem, a new form of force function is constructed to represent infinite stress at the crack tip, and the first four coefficients of the William's series are then computed. Validity and accuracy of this method is fully demonstrated through two benchmark problems. The results show that stress and displacement fields agree very well with the results of other methods. In addition, the coefficients of the William's series show good agreement with the results of existing methods available in the literature.
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