STP1315: Stress History Dependent Localization and Failure Using Continuum Damage Mechanics Concepts

    Horstemeyer, MF
    Senior members, Technical Staff, Center for Materials and Engineering Sciences, Sandia National Laboratories, Livermore, CA

    Revelli, V
    Senior members, Technical Staff, Center for Materials and Engineering Sciences, Sandia National Laboratories, Livermore, CA

    Pages: 22    Published: Jan 1997


    Abstract

    Since the notion of damage was introduced by Kachanov and Rabatnov in the late 1950s and early 1960s, the paradigm to better capture the physics of the internal state of a material has been realized in developing macroscale constitutive relationships for monolithic and composite materials. For ductile metals, damage occurs mainly in the form of void nucleation, growth, and coalescence. Localization and failure occur at two different stages in the deformation history and are very much functions of the void (porosity) evolution, which can be interpreted as the damage evolution, and the stress state history. The damage evolution of a polycrystalline metal is fully coupled to the stress history. In this study, different initial material properties are varied in four different boundary value problems to reflect the stress state and deformation history effects. Special attention is paid to three internal state variable evolution equations; one represents scalar damage, and the other two represent isotropic (scalar) hardening and kinematic (tensorial) hardening. Internal state evolution equations that capture history effects are necessary when trying to solve complex boundary value problems. This constitutive framework is embedded into a finite element formulation to solve such boundary value problems. Mesoscale analyses of A356- T6 aluminum under different stress states and initial material states are used to give insight into the void nucleation, growth, and coalescence issues that arise when formulating an internal state porosity evolution rule within a macroscale framework. This work was based on previous studiesrelated to the four boundary value problems. Numerical calculations were performed to compare to 6061-T6 aluminum notch tension tests with different notched radii. The various notch radii induce different levels of stress triaxiality and allow for correlation of different void growth rules. Numerical calculations of forming limit diagrams for 6061-T6 aluminum compared favorably to experimental results. Finally, penetration analyses were performed with 6061-T6 aluminum disks as targets.

    Keywords:

    continuum damage mechanics, internal state variable, localization, failure, finite element method, boundary value problem, cracking, fatigue (materials), fracture (materials)


    Paper ID: STP11886S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP11886S


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