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Meshfree-Based Fracture Evaluation and Design Tool for Welded Aluminum Ship Structures
Navy STTR FY2010.A
| Sol No.: |
Navy STTR FY2010.A |
| Topic No.: |
N10A-T041 |
| Topic Title: |
Meshfree-Based Fracture Evaluation and Design Tool for Welded Aluminum Ship Structures |
| Proposal No.: |
N10A-041-0438 |
| Firm: |
Advanced Dynamics, Inc.
1500 Bull Lea Road, Suite 203
Lexington, Kentucky 40511-1268 |
| Contact: |
Patrick Hu |
| Phone: |
(859) 699-0441 |
| Web Site: |
www.advanceddynamics-usa.com |
| Abstract: |
The aluminum alloys have low density, relatively high strength, and high strength-to-weight ratio, which brings some major advantages in marine structure design, fabrication, and operations. However, marine ships are subjected to a complex and severe loading, and the typical failure mode of aluminum under extreme dynamics loading such as wave slamming and high velocity impact is ductile fracture. Ductile fracture under extreme loading is different from fatigue under cyclic loading, it results from an excessive force applied to a metal such as aluminum, and the material undergoes large inelastic or plastic deformation before its final structural failure. The numerical simulation of ductile fracture has been a challenge in computational failure mechanics and materials science. Therefore, in the proposed STTR project, a state of the art, multi-fidelity, and efficient meshfree method for ductile fracture developed recently by Dr. Shaofan Li at University of California--Berkeley will be adopted and extended to the modeling and simulation of shear dominated ductile fracture of welded aluminum marine structures under extreme dynamic impact loading, and a corresponding computer software package and tookit will be developed at the same time. The novel methodologies in the proposed projects include 6 tasks: (1) Integrate the modified Gurson-Tvergaard-Needleman (GTN) model into meshfree method for simulation of shear dominated ductile fracture; a corresponding constitutive law containing the welded effects on aluminum alloys will also be taken into account; (2) an efficient meshfree contact algorithm for shear dominated ductile fracture under impact and thermo-mechanical loading will be developed; (3) a new meshfree ductile crack nucleation and propagation will be developed; (4) a new three-dimensional meshfree ductile crack growth in thin shell structures will be developed; (5) a simulation of welding process will be developed that can take into account the welded material anisotropy and heterogeneity, rate dependence, and residual stress effects; (6) an example of ductile fracture in a welded aluminum ship structural component will be presented by using the finite element in the global level, and meshfree in the local level. |
| Benefits: |
Currently, marine structures are designed and built to resist three major failure modes: plastic yielding, buckling, and fatigue. The increasing wide spread use of high strength-to-weight aluminum alloys with low density and relatively high strength in ship structures brings substantial weight saving on one hand and the risk of fracture on the other hand. It has been speculated that the aluminum alloy will replace the steel as the main material in ship fabrication. Marine ships are subjected to a complex and severe loading spectrum including wave loading, sea slap, slamming and impact, vibration, thermal loading, cargo, aircraft landing, weapon reactions, and blast loads, etc. The typical failure mode of aluminum under extreme dynamics loading such as wave slamming and high velocity impact is ductile fracture. Ductile fracture under extreme loading results from an excessive force applied to a metal such as aluminum, and the material undergoes large inelastic or plastically before final fracture.
Because of the complicated physics in ductile fracture of welded aluminum ship structures, the existing commercial finite element (FE) software is not able to provide an accurate solution or prediction on ductile fracture in aluminum ships. Therefore, in this proposed STTR project, we propose to use a state of the art, innovative, and efficient meshfree methodology pioneered by Professor Li at UC Berkeley to develop a ductile fracture evaluation and design tool for welded thin-walled aluminum alloy ship structures that may function under extreme dynamics loading in the presence of material anisotropy, rate dependence, material heterogeneity, and multisite damage. The proposed technology development includes both modeling and simulation methodologies as well as computer software package. The major innovative improvements over currently available methodologies include:
(1) An innovative meshfree methodology will be integrated with the finite element shell modeling for ductile fracture of welded aluminum ship structures with a finite element mesh independent arbitrary crack insertion and propagation capability.
(2) A modified physics-based Gurson-Tvergaard-Needleman (GTN) model and its corresponding inelastic damage constitutive law will be integrated with the meshree methodology to capture the rate dependence and anisotropy in strength, plastic flow and ductility of the welded aluminum material under high velocity impact loading.
(3) FE simulation of the welding process that can take into account of the residual stress effect, material anisotropy, rate dependence, and material heterogeneity.
(4) A computer software package for ductile fracture evaluation and design tool for welded thin-walled aluminum ship will be developed.
Therefore, the methodology and software tookit developed in the proposed project will lead to saving in both time and money without resorting to experimental trials, and provide Navy a next generation tool to model, simulate, and predict the ductile fracture failure of marine structures under extreme dynamics loading, and provide a new design methodology to resist dynamic failure and improve the reliability and safety of marine structures.
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