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In this study, the deformation mechanisms of bulk metallic glass (BMG) foam with around 49% porosity were investigated by using X-Ray Computed Tomography (CT) technique. X-Ray CT experiments were conducted at ESRF Synchrotron Source, Grenoble, France where the in-situ compression testing is possible. The collected CT images were digitally enhanced and the volumetric strain of the foam cells was calculated. The visual analysis of the foam cells was compared with a finite element model to determine whether the foam exhibited any pressure sensitivity. The sample experiences uniform local deformation under compression until a few geometric instabilities in the foam induce local cell bending, followed by multiple shear band formation and localized fracture. Contrary to other reports [1, 2] that suggest plastic buckling in a single narrow crushing band, the majority of the strain the 49% porous sample experiences is from a percolating diffuse brittle crushing along shear bands of the sample. Reports of highly porous samples show a more ductile behavior in individual ligaments because of multiple shear band formation, but commonly fail along a relatively narrow (crushing) band. In moderate porosity foams, this ductility of thin ligaments was rarely observed to occur locally, but before a single crushing band can form, shear bands within highly stressed solid regions propagate until fracture with a similar behavior of a solid sample with very little porosity. However, once the crack encounters another bubble while propagating, it is temporarily blunted by the formation of more shear bands. During this phase, the energy of the system is relieved and redirected to different parts of the foam. Overall, there is a percolating failure of the foam due to relatively rare membrane bending followed by local membrane bursting and cracking into highly stressed nearby solid portions.

Experimental observations and simulations of the mechanical deformation of amorphous metallic foam