Meshfree-Based Fracture Evaluation and Design Tool for Welded Aluminum Ship Structures

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.