Plastic and fracture analysis of engineering materials and welded structures

Stress intensity factor solutions for spot welds and associated kinked cracks in cup specimens and lap-shear specimens are developed from fundamental fracture and plastic analyses. First, global stress intensity factor solutions for spot welds in cup specimens and lap-shear specimens are investigated by finite element analyses. Axisymmetric and three-dimensional finite element models are developed for circular plates to establish the finite element meshes needed to obtain accurate global stress intensity factor solutions. Based on the computational results, a closed-form global stress intensity factor solution is suggested for spot welds in square-cup specimens, and geometric functions to the global stress intensity factor solutions are obtained for spot welds in lap-shear specimens. The computational results also show that the local mode I stress intensity factor of kinked cracks in cup specimens and at critical locations of semi-elliptical kinked cracks in lap-shear specimens increases and then decreases when the kink depth increases. The computational results for lap-shear specimens also indicate that when the spacing between spot welds decreases, the global mode I stress intensity factor solution at the critical locations increases substantially and the mode mixture of the global stress intensity factors changes consequently.;Yield or failure criteria for porous ductile metals and foams are developed from fundamental fracture and plastic analyses. The influence of plastic anisotropy on the plastic behavior of porous ductile metals is investigated by a three-dimensional finite element analysis. A modified anisotropic Gurson yield criterion is proposed. When the strain hardening is considered, the computational results of the macroscopic stress-strain behavior are in agreement with those based on the proposed anisotropic Gurson yield criterion under selected monotonically increasing loading conditions. Finally, the yield or failure behavior of a polymeric foam is investigated under multiaxial loading conditions. A phenomenological yield function is developed for the polymeric foam. The yield function is a linear combination of non-quadratic functions of the relative principal stresses and the second invariant of the deviatoric stress tensor. The yield function can be used to fit the yield or failure behavior of the foam under a full range of loading conditions.