Leiting Dong

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

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, ...

A Simple Locking-Alleviated 4-Node Mixed-CollocationFinite Element with Over-Integration, for Homogeneousor Functionally-Graded or Thick-Section LaminatedComposite Beams

In this study, a simple 4-node locking-alleviated mixed finite element (denoted as CEQ4) is developed, for the modeling of homogeneous or functionally graded or laminated thick-section composite beam structures, without using higher-order (in the thickness direction) or layer-wise zig-zag theories of composite laminates which are widely popularized in current literature. Following the work of [Dong and Atluri (2011)], the present element independently assumes a 5-parameter linearly-varying Cartesian strain field. The independently assumed Cartesian strains are related to the Cartesian strains derived from mesh-based Cartesian displacement interpolations, by exactly enforcing 5 pre-defined constraints at 5 pre-selected collocation points. The constraints are rationally defined to capture the basic kinematics of the 4-node element, and to accurately model each deformation mode of tension, bending, and shear. A 2 by 2 Gauss quadrature is used when each element is used to model a piece of a homogeneous material or structure, but over-integration (using a higher-order Gauss Quadrature, a layer-wise Gauss Quadrature, or a simple Trapezoidal Rule in the thickness direction) is necessary if functionally-graded materials or thick-section laminated composite structures are considered. Through several numerical examples, it is clearly shown that the present CEQ4 is much more accurate than the well-known Pian-Sumihara (1984) element as well as the primal four-node element, for the modeling of homogeneous beams. For functionally-graded materials, the presently-developed element can accurately capture the stress distribution even when very few elements are used; but the Pian-Sumihara element fails, because the assumption of linearly-varying stressfield is generally invalid unless a very fine mesh is used in the thickness direction. 1 Department of Engineering Mechanics, Hohai University, China. 2 King Abdulaziz University, Jeddah, Saudi Arabia. 3 Center for Aerospace Research & Education, University of California, Irvine, Distinguished Adjunct Professor, KAU, Saudi Arabia. 50 Copyright

A Simple Locking-Alleviated 3D 8-NodeMixed-Collocation C 0 Finite Element withOver-Integration, for Functionally-Graded and LaminatedThick-Section Plates and Shells, with & without Z-Pins

Following previous work of [Dong, El-Gizawy, Juhany, Atluri (2014)], a simple locking-alleviated 3D 8-node mixed-collocation C0 finite element (denoted as CEH8) is developed in this study, for the modeling of functionally-graded or laminated thick-section composite plates and shells, without using higher-order or layer-wise zig-zag plate and shell theories which are widely popularized in the current literature. The present C0 element independently assumes an 18-parameter linearly-varying Cartesian strain field. The independently assumed Cartesian strains are related to the Cartesian strains derived from mesh-based Cartesian displacement interpolations, by exactly enforcing 18 pre-defined constraints at 18 preselected collocation points. The constraints are rationally defined to capture the basic kinematics of the 3D 8-node C0 element, and to accurately model each basic deformation mode of tension, bending, shear, and torsion. A 2×2×2 Gauss quadrature is sufficient for evaluating the stiffness matrix of CEH8 C0 3D elements for homogeneous materials, but over-integration (with a higher-order Gauss Quadrature, a layer-wise Gauss Quadrature, or a simple Trapezoidal Rule in the thickness direction) is used for functionally-graded materials or thick-section laminated composite structures with an arbitrary number of laminae. Through several numerical examples, it is clearly shown that the present CEH8 3D C0 element can accurately capture the stress distribution of FG and thick laminated structures with an arbitrary number of laminae even when only one element is used in the thickness direction. In stark contrast to the higher-order or layer-wise zig-zag plate and shell theories, with assumptions for displacement or stress fields in the thickness direction, which may require complicated C1 finite element, the present C0 element can accurately 1 Department of Engineering Mechanics, Hohai University, China. 2 Center for Aerospace Research & Education, University of California, Irvine, USA. 3 King Abdulaziz University, Jeddah, Saudi Arabia. 164 Copyright