SBIR-STTR Award

A software tool for fracture evaluation and load deflection prediction of welded aluminum ship structures subjected to impulsive loading will be developed by enhancing and integrating an existing extended finite element method (XFEM) for dynamic fracture of thin shells in Abaqus. The software package will be able to model arbitrary crack paths as dictated by the physics of the scenario, completely independent of the mesh. This will be accomplished by adding discontinuous displacement and velocity fields arbitrarily within the shell elements via two superposed elements with a set of phantom degrees of freedoms. Explicit time integration with one point quadrature scheme and an hourglass control will be implemented to further simplify the treatment of cracked elements and provide consistent history variables for nonlinear material models. A modified Johnson-Cook model coupled with a nonlocal fracture criterion will be implemented to capture an anisotropic and rate dependent nonlinear material behavior and its associated damage initiation. Global Engineering and Materials, Inc. (GEM) has secured commitments for technical support from the University of Texas at El Paso (UTEP) and Professor Ted Belytschko from Northwestern University (NWU). Dr. Belytschko will provide GEM his stand alone explicit dynamic XFEM tool for shells.

Benefit:
The results from this research will have significant benefits and a wide range of commercial applications in the ship, marine, offshore, automotive and aerospace industries. It will result in 1) a commercially viable, accurate, computationally efficient, and user-friendly tool for fracture damage and residual strength assessment of large scale welded aluminum structures subjected to extreme dynamic loading; 2) a standardized test matrix at the coupon level for quantification of material properties used in the material and fracture models; 3) a virtual testing tool to reduce current certification and qualification costs that are today heavily driven by costly sub-element and full-scale component testing for design certification, and 4) innovative design and fabrication procedures for designing blast resistant structures. The software tool will be of great benefit to 1) ship builders to aid in designing reliable and cost effective aluminum weldments to meet the operating requirements; 2) DOD labs to assess the shock resistance capabilities of welded aluminum structures; and 3) the automotive and aerospace industries to evaluate impact damage and explore new hardening strategies for crashworthiness and other applications. Through a close interaction and alliance partnership with SIMULIA, we will facilitate commercialization of the developed technology and extend its use by the oil industry and civil/architectural engineering firms for the design of lightweight protection system.

Keywords:
shell, shell, Cohesive Model, nonlocal fracture criterion, dynamic fracture, rate dependent plasticity, Crack Growth

A software toolkit for Abaqus (XSHELL) will be developed for fracture evaluation and load deflection prediction of welded aluminum ship structures subjected to impulsive loading. The mesh independent crack description and fracture energy dissipation will be achieved in XSHELL through the implementation of two overlay elements with an embedded cohesive interaction along an arbitrary crack segment without in conformation to the existing finite element mesh. In addition to the implemented Belytschko-Tsay shell elements, new XFEM shell elements will be developed in their triangular and quadrilateral formats that better capture the kinematics of warped elements and curvature. Modified Mohr-Coulomb and a Johnson Cook models coupled with a nonlocal failure theory will be implemented to capture the nonlinear fracture initiation in aluminum alloys. A mixed mode cohesive and crack growth direction law will be used to drive the subsequent crack propagation and its associated energy dissipation. Global Engineering and Materials, Inc. (GEM) has commitments for technical support from Professor Jack Chessa at The University of Texas at El Paso, Professor Ted Belytschko from Northwestern University, and Professor Robert Dodds from University of Illinois at Urbana-Champaign. To help commercialize the XSHELL technology, GEM has also secured endorsement and support from Alcoa and NOV (National Oilwell Varco).

Benefit:
The results from this research will have significant benefits and a wide range of commercial applications in the ship, marine, off-shore, automotive and aerospace industries for sheet metal forming and for crashworthiness analysis. It will result in 1) a commercially viable, accurate, computationally efficient, and user-friendly tool for fracture damage and residual strength assessment of large scale welded aluminum structures subjected to extreme dynamic loading; 2) a standardized test matrix at the coupon level for quantification of material properties used in the material and fracture models; 3) a virtual testing tool to reduce current certification and qualification costs that are today heavily driven by costly sub-element and full-scale component testing for design certification, and 4) innovative design and fabrication procedures for designing blast resistant structures. The software tool will be of great benefit to 1) ship builders to aid in designing reliable and cost effective aluminum weldments to meet the operating requirements; 2) DOD labs to assess the shock resistance capabilities of welded aluminum structures; and 3) the oil and aerospace industries to evaluate impact damage and explore new design options to improve the structural performance under dynamic loading. Through a close interaction and alliance partnership with Alcoa and NOV, we will facilitate and expedite commercialization of the developed technology and extend its use by the oil industry and civil/architectural engineering firms for the design of a lightweight system. The capabilities will be incorporated in Abaqus, one of the most widely used general purpose finite element programs.

Keywords:
Plasticity, nonlocal fracture criterion, Crack Growth, Cohesive Model, crack initiation, dynamic fracture, XFEM, shell