As ffracture mechanics has developed as a discipline, many parameters have been developed to characterize the instability condition. However, a majority of this work has been confined to the investigation of mode 1 fracture. Thus, we have standardized methods for experimentally determining K_(Ic), J_(Ic) and J- resistance curves for mode I crack propagation. However, cracks in real materials can be subjected not just to tensile stresses but to complex stress states so that the development of suitable parameters to characterize mixed-mode crack initiation and propagation is important in the evolution of suitable design criteria. A consistent body of work on mixed mode I/III fracture toughness of materials using modified compact tension specimens is now availalbe. The superposition of mode III loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has little effect or even results in an increase in the fracture toughness. Fracture mechanism maps delineating regions of susceptibility to tensile and shear loads have been proposed to rationalize these trends. In this paper, data on a wider range of materials, including steels, aluminum alloys, metal matrix composites, ceramics and polymers is used to extend and reinforce the fracture mechanism map concept. The concept is also used to explain the mixed - mode impact behavior of materials.
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