Three-Dimensional SGBEM-FEM Alternating Method for Analyzing Fatigue-Crack Growth in and the Life of Attachment Lugs: Fid-Bau Portal

Three-Dimensional SGBEM-FEM Alternating Method for Analyzing Fatigue-Crack Growth in and the Life of Attachment Lugs

Tian, Longgang

AbstractIn the present paper, stress intensity factor (SIF) analyses and fatigue-crack-growth simulations of corner cracks emanating from loaded pinholes of attachment lugs in structural assemblies are carried out for different load cases. A three-dimensional (3D) symmetric Galerkin boundary-element method (SGBEM) and FEM alternating method is developed to analyze the nonplanar growth of these surface cracks under general fatigue. The 3D SGBEM-FEM alternating method involves two very simple and coarse meshes that are independent of each other: (1) a very coarse FEM mesh to analyze the uncracked lug, and (2) a very coarse SGBEM mesh to model only the growing crack surface. By using the SGBEM-FEM alternating method, the nonplanar growth of cracks in 3D (surfaces of discontinuity) up to the failure of structures are efficiently simulated, and accurate estimations of fatigue lives are made. The accuracy and reliability of the SGBEM-FEM alternating method are verified by comparing them to other FEM solutions, as well as experimental data for fatigue-crack growth available in the open literature. The SIF calculations, crack surface evolutions, and fatigue-life estimations are all in good agreement with other detailed FEM solutions and experimental observations. It is noted that for fracture and fatigue analyses of complex 3D structures such as attachment lugs, a pure FEM requires several hundreds of thousands or even millions of elements, whereas the present 3D SGBEM-FEM alternating method requires only up to 1,000 FEM elements and ∼100 SGBEM elements. It thus demonstrates that the present SGBEM-FEM alternating method, among the many Schwartz-Neumann-type alternating methods developed in the past 20–30 years are suitable for analyzing fracture and fatigue-crack propagation in complex 3D structures in a very computationally efficient manner, as well as with very low human labor costs.