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The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band, or dislocation. [1]
En echelon veins can be parallel or subparallel, closely-spaced, overlapping or step-like minor structural features in rock. These step-like features can be faults, or tension fractures, that are oblique to the overall structural trend. They originate as tension fractures that are parallel to the major stress orientation, σ 1, in a shear zone.
Tensile cracks, also referred to as wing cracks (red) grow at an angle from the edges of the shear fracture allowing the shear fracture to propagate by the coalescing of these tensile fractures. Cracks in rock do not form smooth path like a crack in a car windshield or a highly ductile crack like a ripped plastic grocery bag.
When a solid is in tension, its atomic bonds stretch, elastically. Once a critical strain is reached, all the atomic bonds on the fracture plane rupture and the material fails mechanically. The stress at which the solid fractures is the theoretical strength, often denoted as . After fracture, the stretched atomic bonds return to their initial ...
According to Griffith's theory of fracture in tension, the largest flaw or crack will contribute the most to the failure of a material. Strength also depends on the volume of a specimen since flaw size is limited to the size of the specimen's cross section. Therefore, the smaller the specimen (e.g., fibers), the higher the fracture strength.
Fracture of biological materials may occur in biological tissues making up the musculoskeletal system, commonly called orthopedic tissues: bone, cartilage, ligaments, and tendons. Bone and cartilage, as load-bearing biological materials, are of interest to both a medical and academic setting for their propensity to fracture.
Tension, however, accounts for most of the "opposite directions" pull on the plates. As the separating oceanic crust cools over time, it becomes more dense and sinks farther and farther away from the ridge axis. The cooling and sinking ocean crust causes a tensile stress that also helps drive the pulling apart of the plates at the ridge axis.
Stress triaxiality has important applications in fracture mechanics and can often be used to predict the type of fracture (i.e. ductile or brittle) within the region defined by that stress state. A higher stress triaxiality corresponds to a stress state which is primarily hydrostatic rather than deviatoric .