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Fatigue and Fracture
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Under ONR sponsored aluminum hull program, GEM is developing an advanced computational durability assessment framework for characterizing flaw criticality and remaining life of an aluminum ship structural component. Given a critical structural component such as a structural aluminum weldment and an applied cyclic load, a stress-life approach is used first to determine the most probable site for crack initiation. To examine the criticality of the initial flaw and its impact on the subsequent crack propagation life, an extended finite element method (XFEM) coupled with a fatigue crack growth model is implemented to capture arbitrary curvilinear crack growth without user intervention or remeshing and thus provide a user-friendly, reliable tool for predicting component life. The effects from the welding induced residual stress and material heterogeneity in the weldment is characterized using a stress-ratio dependent polygonal crack growth law. The XFEM based fatigue life prediction tool will feature 1) time for crack initiation prediction; 2) arbitrary insertion of initial cracks that are independent of the finite element mesh; 3) characterization of a growing crack without remeshing; and 4) accurate extraction of stress intensity factors for curvilinear crack growth prediction.
Figure 1: Overview of Flaw Assessment and Life Prediction Tool for Aluminum Ship Structures
Fatigue and Fracture Analysis of High Speed Aluminum Ship Structures
Under an ONR sponsored program, GEM has built a multi-level analysis framework which accounts for fatigue crack initiation, propagation, and fracture. The main objective of is to develop an advanced fracture and fatigue analysis tool for aluminum weldments in the presence of 1) arbitrary initial defects; 2) material heterogeneity and nonlinearity; and 3) an initial residual stress field. An extended finite element solution module is implemented in ABAQUS via its user-defined element. A 2D representative welded T- joint is selected with a prescribed transversely cyclic loading. Three distinct elastoplastic material models are used to characterize the mechanical behavior of the base material, the heat affected zone, and the welding zone. The maximum principal stress direction at the critical location is used to determine the orientation of the crack at initiation. Both the crack growth path and the remaining life are computed from the 2D XFEM package under the Paris fatigue crack growth law.
To explore mesh dependency on a curvilinear crack growth, a squared plate subjected to a remote vertical displacement field is shown in Fig. 1. Two inclined initial cracks emanating from the holes are prescribed during the XFEM simulation. As shown in Fig. 2, the curvilinear crack growth paths simulated on a coarse and refined mesh are almost identical which suggest that the crack growth path is insensitive to mesh density.
Figure 2: A Square Plate with Cracks Emanating From Two Small Holes
Figure 3: Multiple Crack Growth Simulation Using XFEM on Refined and Coarse Meshes
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GEM Capabilities
Computational Mechanics
Composite Mechanics
Fatigue and Fracture
Probabilistic Mechanics and Reliability Engineering
Stochastic Mechanics
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