Fracture and Fatigue of Alloys Under Mixed-Mode Loading

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9420511 Hirth This research examines mixed-mode loading effects on the fracture and fatigue behavior of metal alloys. A high purity steel and a special aluminum alloy, for which base-line data already exist, are the focus of the study. Mechanical property measurements include low-cycle fatigue and fracture tests under mixed mode type I-II-III loading, with multiaxial and non proportional loading conditions. Deformation and fracture behavior are characterized by scanning electron microscopy and transmission electron microscopy. Theoretical modeling includes a continuation of dislocation modeling of the onset of failure in the form of a localized shear deformation by a translating and bowing discontinuous tilt wall. Theoretical work employs finite element modeling of crack propagation in terms of a damage mechanism associated with the mode II and mode III loading components. %%% This research is of fundamental importance in material design standards since it establishes the mechanism of degradation of fracture toughness under mixed-mode I-II-III loading. It also examines the role of such loading on damage under low-cycle fatigue. ***