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Computational Mechanics
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GEM has established a strategic partnership with Computational Mechanics Lab at Northwestern University (NWU). We are working closely with Prof. Ted Belytschko in transferring various research tools developed by NWU to the commercial products. In addition, GEM’s personnel have developed various toolkits for the commercial finite element software such as ABAQUS and LS-DYNA to perform stochastic analysis and dynamic failure analysis. We also offer expertise in structural modeling, virtual testing, and response and failure prediction using our customized solution modules within commercial finite element software (ABAQUS/LS-DYNA/NASTRAN). GEM’s personnel have performed large scale structural analysis for advanced structures subjected to thermal, mechanical and extreme dynamic loading. GEM’s personnel have performed structural integrity and durability assessment of roof-mounted sirens subjected to random wind excitation. The predicted hot-spot location agrees well with the crack initiation and propagation site observed from field observations.
Figure 1: Crack Initiation and Propagation of a Siren under Pull-Test
Figure 2: Finite Element Analysis of a Siren Subjected to a Pull Load
GEM is currently developing an eXtended Finite Element Method (XFEM) for residual strength and life prediction of a composite structure with a given set of initial multiple delamination areas. This automated delamination onset and growth prediction tool is implemented within the ABAQUS implicit solver. The unique features of the software product are: 1) the capability for arbitrary insertion of multiple initial delamination cracks into any finite element mesh at either element boundaries or within elements via a PATRAN GUI; 2) simulation of arbitrary crack growth without remeshing; 3) accurate extraction of strain energy release (SERR) rate along an arbitrary crack front with or without closure via a modified VCCT technique; and 4) characterization of delamination onset and growth results via PATRAN and ABAQUS’s CAE. The current XFEM technology is capable to simulate 2D/3D crack growth and generate structural finite element model for multiphase microstructure by means of implicit surface definitions for both external and internal surfaces. The XFEM simulation of crack brunching has been performed with experimental validation.
Figure 3: 2D XFEM Simulation of Crack Propogation
Figure 4: 3D XFEM Simulation of Crack Propogation
Figure 5: Mesh-Independent modeling of Composite RVE using XFEM
Figure 6: Validation of Crack Branching Simulation using XFEM
Fire Simulation and Thermal-Mechanical Damage Prediction Tool for Composite Structures
Under an ONR sponsored SBIR program, GEM along with its team members, Virginia Tech and the University of Buffalo, has developed a coupled thermo-mechanical fire simulation response and damage prediction tool. The package is developed as an add-on toolkit for commercial finite element solvers such as ABAQUS by enhancing, packaging, and integrating existing solution modules. . This tool, for the first time, is able to model fluid-structure coupled response of composite structures to a pool fire and synergistic interaction of multiple failure modes and their compounding effect that contribute to the final catastrophic failure.
Figure 7: Fluid and Structural Coupling in Thermal and Chemical Prediction
Figure 8: Illustration of User-Defined Material Library in ABAQUS
Figure 9: Comparison of Kinking Failure Mechanism of a Compressed Column with Georgia Tech’s Experimental Observation
Whipping Response and Damage Prediction of a Representative Hybrid and Steel Hull
Under an ONR sponsored program, GEM has developed a framework and toolkit to address the dynamic structural failure of advanced ship hulls under shock loadings. We have integrated the current ABAQUS shock analysis module with a composite damage model and developed a fluid-structure interaction model for a ship hull embedded in fluid. A whipping analysis is performed on a hybrid composite hull and its equivalent steel hull. A tradeoff study is performed based on comparison of whipping response and failure mechanism of a hybrid hull with its equivalent steel hull. The mechanism based shock damage prediction tool will increase Navy’s technical knowledge in response of hybrid structures to extreme dynamic loading. This will enable a qualitative evaluation of hybrid hull concepts and optimal hardened design via the numerical simulation.
Figure 10: Failure Initiation and Progression in Steel Longeron and Composite Panel
Figure 11: Failure Progression in a Representative Steel Hull
Reliability Based Structural Design of Damaged Composite Pi-Joints
Under an AF sponsored program, GEM is assisting LM Aero in implementation of XFEM based onset delamination crack prediction module within a probabilistic analysis framework. The integrated package is able to determine the reliability of an existing joint design and predict more robust joints when subjected to predetermined damage level. A parameterized ABAQUS/XFEM model is developed to account for random crack geometry, component geometry, material properties, and applied load. A computational efficiency is greatly enhanced by arbitrary insertion of cracks without changing the original FEM mesh.
Figure 12: Arbitrary 2D/3D Crack Insertion
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GEM Capabilities
Computational Mechanics
Composite Mechanics
Fatigue and Fracture
Probabilistic Mechanics and Reliability Engineering
Stochastic Mechanics
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