Analysis of shear-dominated ultra-low-cycle ductile damage and failure behavior

The paper deals with experimental and numerical characterization of the shear-dominated damage mechanism under ultra-low-cycle loading conditions. A universal uniaxial shear specimen for sheet metal with a double notch is proposed, enabling large deformation without rotation or buckling under both monotonic and cyclic loading. To investigate the influence of different shear loading histories on plasticity, damage, and fracture behavior, various cyclic loading patterns with overload and increased loading have been designed, considering both loading paths and amplitudes. Numerical analysis with a novel anisotropic cyclic plastic-damage continuum model has been performed and compared with experimental observations, including force–displacement responses and local strain fields obtained by the DIC technique. For the cyclic plastic model, a combined isotropic-kinematic hardening law within a modified Chaboche framework is proposed to describe plastic deformation under large strains. Compared to the scalar-based damage model, a damage strain rate tensor within the damage evolution law is employed to capture the shear damage mechanism caused by the growth and coalescence of micro-shear-cracks. Moreover, SEM is employed to characterize the fracture surface features at the micro-level, thereby verifying the proposed damage mechanism.