@phdthesis{,
    author = {Wei, Zhichao},
    title = {Ductile damage and fracture behavior in metal sheets under reverse loading: Experiments, modeling and numerical analysis},
    editor = {},
    booktitle = {},
    series = {},
    journal = {},
    address = {},
    publisher = {},
    edition = {},
    year = {2024},
    isbn = {},
    volume = {},
    number =  {},
    pages = {},
    url = {},
    doi = {},
    keywords = {Ductile damage and fracture, Biaxial non-proportional experiments, Numerical algorithm, Reverse loading, Single-cyclic and bi-cyclic loading, Anisotropic continuum damage model},
    abstract = {This thesis deals with experimental and numerical analysis of ductile damage and fracture behavior under reverse loading conditions. The experimental part includes novel one-axial and biaxial monotonic and reverse experiments conducted on different specimens taken from ductile aluminum alloy EN AW 6082-T6 sheet with a thickness of 4 mm. For this purpose, different one-axis-loaded and biaxially loaded specimens have been newly designed to generate a wide range of stress states under various reverse experiments. An anti-buckling device is used in uniaxial compression tests, and a down-holder is employed in biaxial testing to prevent buckling. The digital image correlation (DIC) technique is used to record and analyze displacements and strain fields, while scanning electron microscopy (SEM) images of fractured surfaces are utilized to verify the proposed damage mechanism. In the numerical part, an anisotropic two-surface cyclic plastic-damage constitutive model based on the framework of Brünig (2003a) is proposed, incorporating combined isotropic-kinematic hardening and softening laws. The plasticity model is further extended to simulate the Bauschinger effect, the strength-differential effect, and the non-hardening effect after shear reverse loading. Moreover, a novel kinematic softening rule based on Brünig's damage strain rate tensor is added to the damage condition to describe the movement of the damage surface. An efficient Euler explicit numerical integration is realized by the inelastic (plastic or plastic-damage) predictor-elastic corrector approach. In-depth discussions are presented on various consistent tangent operators related to numerical integration aimed at achieving convergence in the global Newton-Raphson scheme. The proposed constitutive model is implemented as a user-defined subroutine (UMAT) into the commercial software Ansys. The comparison between experimental and numerical results, encompassing global load-displacement curves and local strain fields, as well as the numerically predicted damage evolution and experimentally obtained SEM images, offers a comprehensive explanation of the influence of reverse loading histories on ductile damage and fracture behavior at both micro- and macro-levels.},
    note = {},
    
    school = {Universität der Bundeswehr München},
    
}