3D/4D fracture mechanics evaluation on shear band of aluminum alloys

The localizations of plastic deformation in shear band which initiated at the ahead of crack tip of 7075 aluminum alloys have been investigated via in-situ fracture tests using synchrotron X-ray tomography. Local crack driving forces and local strain distributions were measured from tomographic images. The distributions of crack-tip opening displacement along a crack front line were found to vary randomly across specimen thickness. This was attributed to the interaction of stress shielding/anti-shielding effects. The strain distributions around crack-tip were quite different from the understanding which was derived by the elastic-plastic fracture mechanics. With further loadings, the development of equivalent strains in shear bands increased leading to the localizations of plastic deformation. The widths of shear band were observed to decrease at the same time. The degree of localization was affected not only by well-known factors such as aging conditions but also polycrystalline texture and crystallographic orientation. Beyond more than ten times as large strain region which is defined by the fracture mechanics, particles were damaged with developing shear band. Thus, extensive damage within shear bands has been induced the complex behavior of crack propagation in practical materials.